Alfalfa seeds were inoculated with a three-strain cocktail of Escherichia coli O157:H7, Salmonell... more Alfalfa seeds were inoculated with a three-strain cocktail of Escherichia coli O157:H7, Salmonella enterica subsp. enterica serovar Typhimurium DT104, or Listeria monocytogenes by immersion to contain ϳ6 to 8 log CFU/g and then treated with a fatty acid-based sanitizer containing 250 ppm of peroxyacid, 1,000 ppm of caprylic and capric acids (Emery 658), 1,000 ppm of lactic acid, and 500 ppm of glycerol monolaurate at a reference concentration of 1ϫ. Inoculated seeds were immersed at sanitizer concentrations of 5ϫ, 10ϫ, and 15ϫ for 1, 3, 5, and 10 min and then assessed for pathogen survivors by direct plating. The lowest concentration that decreased all three pathogens by Ͼ5 log was 15ϫ. After a 3-min exposure to the 15ϫ concentration, populations of E. coli O157:H7, Salmonella Typhimurium DT104, and L. monocytogenes decreased by Ͼ5.45, Ͼ5.62, and Ͼ6.92 log, respectively, with no sublethal injury and no significant loss in seed germination rate or final sprout yield. The components of this 15ϫ concentration (treatment A) were assessed independently and in various combinations to
Wheys from making Camembert cheese were either uncultured or cultured with Penicillium camemberti... more Wheys from making Camembert cheese were either uncultured or cultured with Penicillium camemberti, adjusted to pH 5.0, 5.2, 5.4, 5.6, 6.2, and 6.8, and filter sterilized. Whey samples were inoculated to contain 100 to 500 Listeria monocytogenes (strains Scott A, V7, CA, or OH) cfu/mL and incubated at 6 °C. Counts of L. monocytogenes were obtained by surface plating appropriate dilutions on Tryptose Agar. Listeria monocytogenes failed to grow at or below pH 5.4; except for strains Scott A and OH which grew in cultured whey at pH 5.4 and attained populations of 7.8 × 103 and 5.4 × 104 cfu/mL, respectively, after 35 d of storage. In uncultured whey at pH 5.6, 6.2, and 6.8, populations of L. monocytogenes increased from 7.20 to 7.81, 7.51 to 8.23, and 7.48 to 8.08 log10 cfu/mL, respectively, after 35 d of storage at 6 °C. In cultured whey at pH 5.6, 6.2, and 6.8, numbers of L. monocytogenes increased from 7.53 to 8.13, 7.82 to 8.55, and 7.95 to 8.80 log10 cfu/mL, respectively, after 35 d of storage. Generation times for L. monocytogenes at 6 °C in uncultured whey at pH 5.6, 6.2, and 6.8 ranged between 25.3 and 31.6 h, 14.8 and 21.1 h, and 14.0 and 19.4 h, respectively, depending on the Listeria strain. In contrast, generation times were significantly (p < 0.05) shorter in cultured whey and ranged between 16.6 and 27.4 h, 10.3 and 16.6 h, and 17.4 and 16.3 h at pH values of 5.6, 6.2, and 6.8, respectively.
The objective of this study was to evaluate the recovery of associated and internalized Salmonell... more The objective of this study was to evaluate the recovery of associated and internalized Salmonella by stomaching and grinding broiler skin during exposure at 4 °C and at room temperature, using a two-strain green fluorescent protein (GFP) labeled cocktail of Salmonella Enteritidis. In the first experiment, broiler skins were immediately taken from eviscerated carcasses and exposed to a Salmonella cocktail containing ∼1 × 109 CFU/ml for 0.5, 6, 12, 24, and 48 h at 4 °C. After each exposure, two 1-min stomachings and subsequent grinding of the stomached skin were conducted to quantify loosely associated (from two stomachings) and tightly associated (from grinding) Salmonella on the skin, respectively. Broiler skins exposed to Salmonella for 24 and 48 h were also examined by confocal microscopy before and after the two stomachings. The 1st and 2nd stomachings recovered an average of 71 and 17% of the Salmonella population, respectively, with an additional 12% of the cells recovered after subsequent grinding, regardless of incubation time. Based on the confocal images, most Salmonella were removed after two stomachings, however a few cells further penetrated from 9 to 29 μm into the skin. In the second experiment, broiler skins were immersed in the same two-strain Salmonella cocktail (∼1 × 108 cells/ml) and dip-inoculated for 2 min with/without stomaching at room temperature. Based on the confocal images, Salmonella penetrated the flat skin surfaces and crevices up to 10 and 68 μm without stomaching, respectively, and up to 62 and 132 μm with stomaching. The presence of free-floating Salmonella cells in the skin crevices indicates that entrapped water is important for bacterial translocation in poultry skin. These findings indicated that extent of observable Salmonella association, penetration, and subsequent recovery from poultry skin is related to both surface topography of poultry skin and method of sample processing.
Work was conducted to validate performance of the ANSR ® for Listeria monocytogenes method in sel... more Work was conducted to validate performance of the ANSR ® for Listeria monocytogenes method in selected food and environmental matrixes. This DNA-based assay involves amplification of nucleic acid via an isothermal reaction based on nicking enzyme amplification technology. Following single-step sample enrichment for 16-24 h for most matrixes, the assay is completed in 40 min using only simple instrumentation. When 50 distinct strains of L. monocytogenes were tested for inclusivity, 48 produced positive results, the exceptions being two strains confirmed by PCR to lack the assay target gene. Forty-seven nontarget strains (30 species), including multiple non-monocytogenes Listeria species as well as non-Listeria, Gram-positive bacteria, were tested, and all generated negative ANSR assay results.
Pathogen thermal inactivation models currently available to and used by industry consider only th... more Pathogen thermal inactivation models currently available to and used by industry consider only the present state of the product when predicting inactivation rates. However, bacteria subjected to sublethal thermal injury can develop partial protection against lethal temperatures. The objective of this study was to extend the capabilities of a previously published path-dependent Salmonella inactivation model by accounting for longer sublethal heating periods and different substrates and to test this new model against independent data. Ground samples of irradiated (.10 kGy) turkey breast, beef round, and pork loin were inoculated with an eight-serovar Salmonella cocktail and subjected to 53 nonisothermal treatments (in triplicate) that combined a linear heating rate (1, 2, 3, 4, or 7 K/min), a variable length sublethal holding period (at 40, 45, or 50uC), a lethal holding temperature (55, 58, 61, or 64uC), and a nominal target kill (3-or 5-log reductions) (n~159 for each meat species). When validated against nonisothermal data from similar treatments, traditional state-dependent model predictions resulted in root mean squared errors (RMSEs) of 2.9, 2.2, and 4.6 log CFU/g for turkey, beef, and pork, respectively. RMSEs for the new pathdependent model were 0.90, 0.81, and 0.82 log CFU/g for the same species, respectively, with reductions in error of 63 to 82% relative to the state-dependent model. This new path-dependent model can significantly reduce error from the state-dependent model and could become a useful tool for assuring product safety, particularly relative to slow heating processes.
An automated dead-end (single pass, no recirculation) ultrafiltration device, the Portable Multi-... more An automated dead-end (single pass, no recirculation) ultrafiltration device, the Portable Multi-use Automated Concen tration System (PMACS), was evaluated as a means to concentrate Escherichia coli 0157:H7 from 40 liters of simulated commercial lettuce wash water. The assessment included generating, sieving, and concentrating sanitizer-free lettuce wash water, either uninoculated or inoculated with green fluorescent protein-transformed E. coli Oi57:H7 at a high (1.00 log CFU/ml) or low (-1.00 log CFU/ml) concentration. Cells collected within the filters were recovered in approximately 400 ml of buffer to create lettuce wash retentates. The extent of concentration was determined by viable plate counts using a medium selective for the transformed E. coli 0157:H7. The samples were qualitatively analyzed for£. coli 0157:H7 according to the U.S. Food and Drug Administration Bacteriological Analytical Manual enrichment method and with an electrochemiluminescence immunoassay. This concentration method was then evaluated in a pilot-scale production line at Michigan State University using chlorinated (100, 30, and 10 ppm of available chlorine) lettuce wash water. The total PMACS processing times were 82 + 6 and 65+5 min for sanitizer-free and chlorinated washes, respectively. Overall, E. coli 0157:H7 populations were approximately 2 log higher in retentates than in unconcentrated lettuce wash samples. The higher E. coli 0157:H7 levels in the retentates enabled cultural and electrochemiluminescence immunoassay detection in some samples when the corresponding lettuce wash samples were negative. When combined with standard and rapid detection methods, the PMACS concentration method may provide a means to enhance pathogen monitoring of produce wash water.
Chemical sanitizers are usually added to dump tank water to minimize cross-contamination during t... more Chemical sanitizers are usually added to dump tank water to minimize cross-contamination during tomato packing. However, the efficacy of sanitizers continues to be questioned. This study assessed the ability of six commonly used sanitizers (40 ppm of peroxyacetic acid, 40 ppm of mixed peracid, 40 ppm of available chlorine alone or acidified to pH 6.0 with citric acid or T-128, and electrolyzed water containing 40 ppm of available chlorine at pH 6.7) to reduce Salmonella on tomatoes, in wash water, and on equipment surfaces using a pilot-scale processing line. Red round tomatoes (11.3 kg) were dip inoculated to contain Salmonella at , 6 log CFU/g, air dried for 2 h, treated for 2 min in a 3.3-m-long dump tank and then dried on a roller conveyor, with sanitizer-free water serving as the control. Tomato and water samples were collected at 15-s intervals during washing with additional dump tank, water tank, and roller conveyor surface samples collected after washing. All samples were appropriately neutralized, diluted, and surface plated on Trypticase soy agar containing 0.6% yeast extract, 0.05% ferric ammonium citrate, and 0.03% sodium thiosulfate with or without membrane filtration to enumerate Salmonella. All six sanitizer treatments were more efficacious than the water control (P # 0.05), with chlorine plus citric acid yielding the greatest Salmonella reduction on tomatoes (3.1 log CFU/g). After processing, all sanitizer wash solutions contained significantly lower (P # 0.05) levels of Salmonella than the water control (3.0 log CFU/ml). The four chlorine-based sanitizer treatments yielded significantly lower Salmonella populations (P # 0.05) in the wash solution compared with peroxyacetic acid and mixed peracid. After processing with sanitizers, Salmonella populations decreased to nondetectable levels (,0.2 log CFU/100 cm 2) on the equipment surfaces.
International Journal of Food Microbiology, Feb 1, 2016
Onions are one of the most widely utilized vegetables worldwide, with demand for fresh-cut onions... more Onions are one of the most widely utilized vegetables worldwide, with demand for fresh-cut onions steadily increasing. Due to heightened safety concerns and consumer demand, the implications of sanitizing and packaging on fresh-cut onion safety and quality need to be better understood. The objective of this study was to investigate the effect of produce sanitizers, in-package atmospheres, and their interactions on the growth of Salmonella Typhimurium, mesophilic aerobic bacteria, yeast and mold, and the physico-chemical quality of diced onions to determine the best sanitizer and in-package atmosphere combination for both safety and quality. Diced onions were inoculated or not with S. Typhimurium, sanitized in sodium hypochlorite, peroxyacetic acid, or liquid chlorine dioxide, and then packaged in either polylactic acid bags containing superatmospheric O2, elevated CO2/reduced O2, or air, or in polyethylene terephthalate snap-fit containers. Throughout 14days of storage at 7°C, packaged diced onions were assessed for their safety (S. Typhimurium), and quality (mesophilic aerobic bacteria, yeasts and molds, physico-chemical analyses, and descriptive and consumer acceptance sensory panels). While sanitizer affected (P<0.05) fewer parameters (S. Typhimurium, mesophiles, yeasts and molds, headspace CO2, weight loss, and pH), in-package atmosphere had a significant (P<0.05) effect on all parameters evaluated. Two-way interactions between sanitizer and atmosphere that affected S. Typhimurium and pH were identified whereas 3-way interactions (sanitizer, atmosphere and time) were only observed for headspace CO2. Sodium hypochlorite and elevated CO2/reduced O2 was the best sanitizer and in-package atmosphere combination for enhancing the safety and quality of packaged diced onions. In addition, this combination led to diced onions acceptable for purchase after 2weeks of storage by trained and consumer panels.
Brick cheese was made by the washedcurd procedure from pasteurized whole milk inoculated to conta... more Brick cheese was made by the washedcurd procedure from pasteurized whole milk inoculated to contain ca. 1 x 102 to 1 x 103 Listeria monocytogenes [strain Scott A, Ohio, V7, or California]/ml. Cheeses were ripened (15°C/95% relative humidity) with a surface smear for 2, 3, or 4 wk to simulate production of mild, aged, or "Limburger-like" brick cheese, respectively, and then stored an additional 20 to 22 wk at 10°C. Populations of strains Scott A, Ohio, V7, and California increased 1.89, 1.72, .83, and .86 orders of magnitude, respectively, following completion of brining ca. 32 h after the start of cheese making. All four L. monocytogenes strains leached from cheese into brine during 24 h and survived in brine at 10*C at least 5 d after removal of cheese. Strains Scott A and Ohio grew rapidly during the initial 2 wk of smear development and attained maximum populations of ca. 6.6 and 6.2, 7.0 and 6.9, and 5.6 and 5.1 logl0/g in 4-wkold slice (pH 6.0 to 6.5), surface (pH 6.5 to 6.9), and interior (pH 5.6 to 6.2) samples of cheese, respectively. Numbers of strains Scott A and Ohio generally decreased 1-to 7-fold during 20 to 22 wk at 10°C. Strains V7 and California failed to grow appreciably in any cheese during or after smear development, despite pH of 6.8 to 7.4 in fully ripened cheese; the strains were never isolated from 2-and 3wk-old cheese and with direct plating were detected sporadically at levels gen
Duplicate lots of cold-pack cheese food were manufactured, according to nine different formulatio... more Duplicate lots of cold-pack cheese food were manufactured, according to nine different formulations, inoculated to contain ca. 5 x 102 Listeria monocytogenes (strains Scott A, V7, California or Ohio) colony forming units (CFU)/g and stored at 4°C. L. monocytogenes in cheese food was enumerated by surface-plating appropriate dilutions made in tryptose broth containing 2% (w/v) sodium citrate (TBC) on McBride Listeria Agar (MLA). Initial TBC dilutions were stored at 3°C and surface-plated on MLA after 2, 4, 6 and 8 weeks if the organism was not quantitated by direct plating of the original samples. Selected Listeria colonies were confirmed biochemically. Populations of L. monocytogenes in cheese food manufactured without preservatives or acidifying agents generally decreased less than 10-fold after 182 d of storage. However, numbers of L. monocytogenes steadily decreased in cheese food containing 0.30% sorbic acid or 0.30% sodium propionate and which was acidified to pH 5.0 to 5.1 with lactic and/or acetic acid. In cheese food preserved with 0.30% sorbic acid, L. monocytogenes survived an average of 130 d in non-acidified cheese food and 112, 93 or 74 d in cheese food acidified with lactic acid, lactic plus acetic acid, or acetic acid, respectively. When 0.30% sodium propionate was substituted for sorbic acid, L. monocytogenes survived an average of 142 d in non-acidified cheese food and 118, 103 or 98 d in cheese food acidified with lactic, acetic, or lactic plus acetic acid, respectively. Since 1983, at least 150 cases of listeriosis, including 54 deaths, resulted from consumption of pasteurized milk (17) and Mexican-style cheese (20) contaminated with Listeria monocytogenes. Recently, another outbreak reported in Switzerland resulted from consumption of Vacherin Mont d'Or soft-ripened cheese (13) and caused at least 10 cases of listeriosis, including two deaths. Increased surveillance of the dairy industry by the Food and Drug Administration, prompted by outbreaks of listeriosis associated with dairy products, has lead to isolation of L. monocytogenes from a variety of domestic cheeses including Liederkranz (2,3), Mexican-style (1,7), Ricotta (22) and Cheddar (22), as well as Brie (4,5,6,9), semi-soft (8) and soft-ripened cheese (8) imported from France. When these findings are considered along with numerous isolations of L. monocytogenes from the dairy factory environment, clearly, this organism poses a serious threat to the cheese industry. Cold-pack cheese food is defined by regulation with a Standard of Identity; Title 21, part 133.124. (18). Several dairy ingredients used in the manufacture of cold-pack cheese food, i.e. Cheddar cheese, nonfat dry milk, and dried whey, could serve as vehicles for contamination of the finished product with L. monocytogenes. Currently, Cheddar cheese manufactured from raw milk can be used in cold-pack cheese food if the cheese is ripened at > 35 °F (1.7°C) for > 60 d to eliminate pathogenic organisms (18). However, experimental evidence has shown that L. monocytogenes can survive as long as 434 d in Cheddar cheese ripened under these conditions (25). In addition, a recall because of contamination with L. monocytogenes was recently issued for raw milk Cheddar cheese which was properly ripened (22). Another study (75) showed that L. monocytogenes can survive as long as 84 d in nonfat dry milk manufactured from pasteurized skim milk inoculated to contain ca. 105 colony forming units (CFU)/ml. Ryser and Marth (26) demonstrated that L. monocytogenes can grow to levels of ca. 108 CFU/ml in filter-sterilized whey. Based on these results, the pathogen would likely survive during spray-drying of fluid whey. Recently, salted (1.2 and 2.5% NaCl) and unsalted butter were manufactured from pasteurized cream inoculated to contain ca. 104 to 105 L. monocytogenes strain Scott A CFU/g (28). After 70 d of storage at-18, 4 and 13°C, the organism was present at levels of 3.22, 5.26 and 5.84 logio CFU/g of butter, respectively. Although L. monocytogenes has yet to be isolated from commercially produced cold-pack cheese food, ingredients used to manufacture this product are clearly capable of harboring the bacterium. The presence of L. monocytogenes in coldpack cheese food is of special concern since this product receives no further heat treatment or aging and is normally consumed shortly after manufacture. Recent recalls of Lwfen'a-contaminated cheeses have
Cottage cheese was made by the short-set procedure in pilotplant-sized vats from pasteurized skim... more Cottage cheese was made by the short-set procedure in pilotplant-sized vats from pasteurized skim milk inoculated to contain 10 4-10 5 Listeria monocytogenes (strains Scott A or V7)/ ml. Half the curd from each trial (two trials with each strain of L. monocytogenes) was creamed and half remained uncreamed. Numbers of L. monocytogenes were determined by surface-plating samples diluted in Tryptose Broth (TB) on McBride's Listeria Agar (MLA). Initial TB dilutions were then stored at 3°C and plated on MLA after 2, 4, 6 and 8 weeks or until L. monocytogenes was recovered. Selected L. monocytogenes colonies from each sample were serologically confirmed. Results for both strains indicate that during manufacture, numbers of L. monocytogenes remained relatively constant until after cooking of curd was completed. All samples analyzed after cooking curd 30 min at 57.2°C (135°F) contained fewer viable L. monocytogenes than could be detected by our methods (10 or 100 CFU/g or ml). Both strains were recovered from cold-enrichment samples, indicating that small numbers of the organism survived the cheesemaking process. Using direct plating onto MLA, L. monocytogenes was recovered from 43 of 112 (38.4%) cottage cheese samples during storage at 3°C for up to 28 d. After cold-enrichment in TB for up to 8 weeks, 59 of 112 (52.7%) samples were positive forL. monocytogenes. Greater numbers of L. monocytogenes, particularly strain Scott A, were found in creamed rather than uncreamed cottage cheese; however, numbers seldom exceeded 100/g. Listeria monocytogenes is a potential foodborne pathogen which can cause abortions in pregnant women and meningitis or meningio-encephalitis in immunocompromised men and women (6,13,14). In dairy cattle, L. monocytogenes can cause mastitis and abortion, leading to excretion of the organism in milk from the infected animal (4,5,15). Evidence for the role of milk in transmission of L. monocytogenes from infected dairy cattle to man has appeared in European literature. The first reported massive outbreak of human listeriosis occurred in Halle, Germany and was followed by epidemics in Jena, Germany and Prague, Czechoslovakia (14). Consumption of Listeriacontaminated raw milk was believed to be the cause of human illness.
ABSTRACT Microbial challenge studies using nonpathogenic surrogates provide a practical means for... more ABSTRACT Microbial challenge studies using nonpathogenic surrogates provide a practical means for validating thermally based pathogen controls for low-moisture foods. Because the relative thermal resistance, or kill ratio, of Enterococcus faecium NRRL B-2354 (a nonpathogenic surrogate) to Salmonella is greatly influenced by food composition, this study assessed relative thermal resistance of a five-strain Salmonella cocktail and E. faecium in skim milk powder (SMP), lactose-free skim milk powder (LSMP), 90% milk protein isolate (MPI), and lactose powder (LP). The impact of sugar composition (lactose versus glucose-galactose) on resuscitation of bacterial survivors, by using SMP and LSMP, was also determined. Dairy powders were inoculated with agar-grown cultures, mixed, preequilibrated at 0.25 water activity (aw), ground to achieve homogeneity, reequilibrated, and subjected to isothermal treatment. After enumeration on nonselective differential media, log-linear and Bigelow models were fit to the survivor data via one-step global regression. The aw changes and glass transition temperature were assessed at elevated temperatures by using uninoculated, equilibrated powder samples. Estimated D90°C-values were approximately two times higher for E. faecium (P < 0.05) than for Salmonella in SMP, LP, and MPI, but statistically similar (P > 0.05) in LSMP. Addition of sugars to recovery media did not influence survivor resuscitation from heat-treated SMP and LSMP, confirming that microbial inactivation was impacted primarily by the thermal treatment, not the recovery step. Thermally induced changes in aw were seen only for LP and MPI, with the glass transition temperature observed only for SMP and MPI. In conclusion, rather than always requiring greater lethality of E. faecium than Salmonella, these findings suggest that sufficient pathogen controls for low-moisture foods can also be validated by thoroughly documenting the appropriate kill ratios of E. faecium to Salmonella. HIGHLIGHTS
ABSTRACT Use of silver nanoparticles (Ag NPs) in pesticides may lead to residual levels in food c... more ABSTRACT Use of silver nanoparticles (Ag NPs) in pesticides may lead to residual levels in food crops, thus raising food safety and environmental concerns. Because little is known about Ag NP behavior in wash water during typical commercial washing of fresh produce, this study assessed the temporal changes in Ag NP behavior when exposed to 2 to 100 mg/L free chlorine (Cl2) in simulated lettuce wash water for up to 10 days. Aggregate size and zeta potential of Ag NPs (5 mg/L) were evaluated in the presence and absence of dissolved lettuce extract (DLE, 0.1%), with Ag NPs in deionized water serving as the control treatment. In the presence of chlorine, greater aggregation of Ag NPs occurred over time (49 to 431 nm) compared with the control treatment (P < 0.05). Lower zeta potentials (−39 to −95 mV) were observed in the chlorine-only treatments, likely due to the formation of AgCl particles. Larger aggregates and lower zeta potentials were also observed in DLE (84 to 273 nm and −28 to −32 mV, respectively), as compared with the control treatment. After 7 to 10 days, larger aggregates were seen in the chlorine-only treatments as compared with the DLE treatments, despite lower zeta potentials, probably facilitated by nucleation and crystal growth of AgCl. Transmission electron microscopy with energy dispersive spectroscopy confirmed the formation of AgCl-Ag NP composite particles with chlorine and the embedding of AgCl and Ag NPs in the DLE matrix. Thus, DLE might stabilize and protect Ag NPs from chlorine. These findings indicate that chlorine and plant-released organic material can substantially change the behavior of Ag NPs, which may, in turn, impact both removal from fresh-cut produce during washing and their environmental fate. HIGHLIGHTS
Recent work by epidemiologists and microbiologists has uncovered several hitherto unrecognized fo... more Recent work by epidemiologists and microbiologists has uncovered several hitherto unrecognized food-borne bacterial pathogens of public health significance. One of these, Listeria monocytogenes, has attracted considerable attention because of two major cheese-related outbreaks of listeriosis that were characterized by cases of meningitis, abortion, and perinatal septicemia. Thus far, L. monocytogenes has been responsible for well over 300 reported cases of food-borne listeriosis, including about 100 deaths, and has cost the dairy industry alone more than 66 million dollars as a result of product recalls. The ability of L. monocytogenes to grow at refrigeration temperatures, coupled with appearance of the pathogen in raw and processed meats, as well as poultry, vegetables, and seafood, makes this bacterium a serious threat to susceptible consumers and to the entire food industry. Yersinia enterocolitica, another psychrotrophic food-borne pathogen of recent concern, was linked to several outbreaks of yersiniosis associated with consumption of both raw and pasteurized milk, as well as contaminated water. Food-borne infections involving Y. enterocolitica typically result in enterocolitis, which may be mistaken for acute appendicitis. Unfortunately, inadvertent removal of healthy appendixes from victims of food-borne yersiniosis is all too common. Although known for many years, Campylobacter jejuni has only recently been recognized as a food-borne pathogen and a leading cause of gastroenteritis in the United States. Notable outbreaks of campylobacteriosis linked to consumption of raw milk, cake icing, eggs, poultry, and beef have underscored the need for thorough cooking and proper handling of raw products.(ABSTRACT TRUNCATED AT 250 WORDS)
Listeria monocytogenes first emerged as a serious threat to the dairy industry in 1985 when a maj... more Listeria monocytogenes first emerged as a serious threat to the dairy industry in 1985 when a major outbreak of listeriosis was traced to consumption of soft Mexican-style cheese in southern California, with other dairy-related outbreaks primarily involving pasteurized milk and certain soft cheeses prepared from raw milk having since been reported. Listeria monocytogenes causes abortion and perinatal septicemia in pregnant women and meningitis in the elderly and immunocompromised patients; it can also produce clinical and subclinical mastitis in ruminant animals, with about 2.5–5% of the raw milk supply found positive for this pathogen. Listeria monocytogenes is endemic to dairy farms and to a lesser extent dairy processing facilities where this pathogen is typically considered a postpasteurization contaminant. Unlike many other bacterial foodborne pathogens, L. monocytogenes can grow in milk at refrigeration temperatures and reach potentially infectious levels in certain high-moisture and surface-ripened cheeses. However, barring postpasteurization contamination, properly pasteurized fluid milk products will be free of Listeria.
Alfalfa seeds were inoculated with a three-strain cocktail of Escherichia coli O157:H7, Salmonell... more Alfalfa seeds were inoculated with a three-strain cocktail of Escherichia coli O157:H7, Salmonella enterica subsp. enterica serovar Typhimurium DT104, or Listeria monocytogenes by immersion to contain ϳ6 to 8 log CFU/g and then treated with a fatty acid-based sanitizer containing 250 ppm of peroxyacid, 1,000 ppm of caprylic and capric acids (Emery 658), 1,000 ppm of lactic acid, and 500 ppm of glycerol monolaurate at a reference concentration of 1ϫ. Inoculated seeds were immersed at sanitizer concentrations of 5ϫ, 10ϫ, and 15ϫ for 1, 3, 5, and 10 min and then assessed for pathogen survivors by direct plating. The lowest concentration that decreased all three pathogens by Ͼ5 log was 15ϫ. After a 3-min exposure to the 15ϫ concentration, populations of E. coli O157:H7, Salmonella Typhimurium DT104, and L. monocytogenes decreased by Ͼ5.45, Ͼ5.62, and Ͼ6.92 log, respectively, with no sublethal injury and no significant loss in seed germination rate or final sprout yield. The components of this 15ϫ concentration (treatment A) were assessed independently and in various combinations to
Wheys from making Camembert cheese were either uncultured or cultured with Penicillium camemberti... more Wheys from making Camembert cheese were either uncultured or cultured with Penicillium camemberti, adjusted to pH 5.0, 5.2, 5.4, 5.6, 6.2, and 6.8, and filter sterilized. Whey samples were inoculated to contain 100 to 500 Listeria monocytogenes (strains Scott A, V7, CA, or OH) cfu/mL and incubated at 6 °C. Counts of L. monocytogenes were obtained by surface plating appropriate dilutions on Tryptose Agar. Listeria monocytogenes failed to grow at or below pH 5.4; except for strains Scott A and OH which grew in cultured whey at pH 5.4 and attained populations of 7.8 × 103 and 5.4 × 104 cfu/mL, respectively, after 35 d of storage. In uncultured whey at pH 5.6, 6.2, and 6.8, populations of L. monocytogenes increased from 7.20 to 7.81, 7.51 to 8.23, and 7.48 to 8.08 log10 cfu/mL, respectively, after 35 d of storage at 6 °C. In cultured whey at pH 5.6, 6.2, and 6.8, numbers of L. monocytogenes increased from 7.53 to 8.13, 7.82 to 8.55, and 7.95 to 8.80 log10 cfu/mL, respectively, after 35 d of storage. Generation times for L. monocytogenes at 6 °C in uncultured whey at pH 5.6, 6.2, and 6.8 ranged between 25.3 and 31.6 h, 14.8 and 21.1 h, and 14.0 and 19.4 h, respectively, depending on the Listeria strain. In contrast, generation times were significantly (p < 0.05) shorter in cultured whey and ranged between 16.6 and 27.4 h, 10.3 and 16.6 h, and 17.4 and 16.3 h at pH values of 5.6, 6.2, and 6.8, respectively.
The objective of this study was to evaluate the recovery of associated and internalized Salmonell... more The objective of this study was to evaluate the recovery of associated and internalized Salmonella by stomaching and grinding broiler skin during exposure at 4 °C and at room temperature, using a two-strain green fluorescent protein (GFP) labeled cocktail of Salmonella Enteritidis. In the first experiment, broiler skins were immediately taken from eviscerated carcasses and exposed to a Salmonella cocktail containing ∼1 × 109 CFU/ml for 0.5, 6, 12, 24, and 48 h at 4 °C. After each exposure, two 1-min stomachings and subsequent grinding of the stomached skin were conducted to quantify loosely associated (from two stomachings) and tightly associated (from grinding) Salmonella on the skin, respectively. Broiler skins exposed to Salmonella for 24 and 48 h were also examined by confocal microscopy before and after the two stomachings. The 1st and 2nd stomachings recovered an average of 71 and 17% of the Salmonella population, respectively, with an additional 12% of the cells recovered after subsequent grinding, regardless of incubation time. Based on the confocal images, most Salmonella were removed after two stomachings, however a few cells further penetrated from 9 to 29 μm into the skin. In the second experiment, broiler skins were immersed in the same two-strain Salmonella cocktail (∼1 × 108 cells/ml) and dip-inoculated for 2 min with/without stomaching at room temperature. Based on the confocal images, Salmonella penetrated the flat skin surfaces and crevices up to 10 and 68 μm without stomaching, respectively, and up to 62 and 132 μm with stomaching. The presence of free-floating Salmonella cells in the skin crevices indicates that entrapped water is important for bacterial translocation in poultry skin. These findings indicated that extent of observable Salmonella association, penetration, and subsequent recovery from poultry skin is related to both surface topography of poultry skin and method of sample processing.
Work was conducted to validate performance of the ANSR ® for Listeria monocytogenes method in sel... more Work was conducted to validate performance of the ANSR ® for Listeria monocytogenes method in selected food and environmental matrixes. This DNA-based assay involves amplification of nucleic acid via an isothermal reaction based on nicking enzyme amplification technology. Following single-step sample enrichment for 16-24 h for most matrixes, the assay is completed in 40 min using only simple instrumentation. When 50 distinct strains of L. monocytogenes were tested for inclusivity, 48 produced positive results, the exceptions being two strains confirmed by PCR to lack the assay target gene. Forty-seven nontarget strains (30 species), including multiple non-monocytogenes Listeria species as well as non-Listeria, Gram-positive bacteria, were tested, and all generated negative ANSR assay results.
Pathogen thermal inactivation models currently available to and used by industry consider only th... more Pathogen thermal inactivation models currently available to and used by industry consider only the present state of the product when predicting inactivation rates. However, bacteria subjected to sublethal thermal injury can develop partial protection against lethal temperatures. The objective of this study was to extend the capabilities of a previously published path-dependent Salmonella inactivation model by accounting for longer sublethal heating periods and different substrates and to test this new model against independent data. Ground samples of irradiated (.10 kGy) turkey breast, beef round, and pork loin were inoculated with an eight-serovar Salmonella cocktail and subjected to 53 nonisothermal treatments (in triplicate) that combined a linear heating rate (1, 2, 3, 4, or 7 K/min), a variable length sublethal holding period (at 40, 45, or 50uC), a lethal holding temperature (55, 58, 61, or 64uC), and a nominal target kill (3-or 5-log reductions) (n~159 for each meat species). When validated against nonisothermal data from similar treatments, traditional state-dependent model predictions resulted in root mean squared errors (RMSEs) of 2.9, 2.2, and 4.6 log CFU/g for turkey, beef, and pork, respectively. RMSEs for the new pathdependent model were 0.90, 0.81, and 0.82 log CFU/g for the same species, respectively, with reductions in error of 63 to 82% relative to the state-dependent model. This new path-dependent model can significantly reduce error from the state-dependent model and could become a useful tool for assuring product safety, particularly relative to slow heating processes.
An automated dead-end (single pass, no recirculation) ultrafiltration device, the Portable Multi-... more An automated dead-end (single pass, no recirculation) ultrafiltration device, the Portable Multi-use Automated Concen tration System (PMACS), was evaluated as a means to concentrate Escherichia coli 0157:H7 from 40 liters of simulated commercial lettuce wash water. The assessment included generating, sieving, and concentrating sanitizer-free lettuce wash water, either uninoculated or inoculated with green fluorescent protein-transformed E. coli Oi57:H7 at a high (1.00 log CFU/ml) or low (-1.00 log CFU/ml) concentration. Cells collected within the filters were recovered in approximately 400 ml of buffer to create lettuce wash retentates. The extent of concentration was determined by viable plate counts using a medium selective for the transformed E. coli 0157:H7. The samples were qualitatively analyzed for£. coli 0157:H7 according to the U.S. Food and Drug Administration Bacteriological Analytical Manual enrichment method and with an electrochemiluminescence immunoassay. This concentration method was then evaluated in a pilot-scale production line at Michigan State University using chlorinated (100, 30, and 10 ppm of available chlorine) lettuce wash water. The total PMACS processing times were 82 + 6 and 65+5 min for sanitizer-free and chlorinated washes, respectively. Overall, E. coli 0157:H7 populations were approximately 2 log higher in retentates than in unconcentrated lettuce wash samples. The higher E. coli 0157:H7 levels in the retentates enabled cultural and electrochemiluminescence immunoassay detection in some samples when the corresponding lettuce wash samples were negative. When combined with standard and rapid detection methods, the PMACS concentration method may provide a means to enhance pathogen monitoring of produce wash water.
Chemical sanitizers are usually added to dump tank water to minimize cross-contamination during t... more Chemical sanitizers are usually added to dump tank water to minimize cross-contamination during tomato packing. However, the efficacy of sanitizers continues to be questioned. This study assessed the ability of six commonly used sanitizers (40 ppm of peroxyacetic acid, 40 ppm of mixed peracid, 40 ppm of available chlorine alone or acidified to pH 6.0 with citric acid or T-128, and electrolyzed water containing 40 ppm of available chlorine at pH 6.7) to reduce Salmonella on tomatoes, in wash water, and on equipment surfaces using a pilot-scale processing line. Red round tomatoes (11.3 kg) were dip inoculated to contain Salmonella at , 6 log CFU/g, air dried for 2 h, treated for 2 min in a 3.3-m-long dump tank and then dried on a roller conveyor, with sanitizer-free water serving as the control. Tomato and water samples were collected at 15-s intervals during washing with additional dump tank, water tank, and roller conveyor surface samples collected after washing. All samples were appropriately neutralized, diluted, and surface plated on Trypticase soy agar containing 0.6% yeast extract, 0.05% ferric ammonium citrate, and 0.03% sodium thiosulfate with or without membrane filtration to enumerate Salmonella. All six sanitizer treatments were more efficacious than the water control (P # 0.05), with chlorine plus citric acid yielding the greatest Salmonella reduction on tomatoes (3.1 log CFU/g). After processing, all sanitizer wash solutions contained significantly lower (P # 0.05) levels of Salmonella than the water control (3.0 log CFU/ml). The four chlorine-based sanitizer treatments yielded significantly lower Salmonella populations (P # 0.05) in the wash solution compared with peroxyacetic acid and mixed peracid. After processing with sanitizers, Salmonella populations decreased to nondetectable levels (,0.2 log CFU/100 cm 2) on the equipment surfaces.
International Journal of Food Microbiology, Feb 1, 2016
Onions are one of the most widely utilized vegetables worldwide, with demand for fresh-cut onions... more Onions are one of the most widely utilized vegetables worldwide, with demand for fresh-cut onions steadily increasing. Due to heightened safety concerns and consumer demand, the implications of sanitizing and packaging on fresh-cut onion safety and quality need to be better understood. The objective of this study was to investigate the effect of produce sanitizers, in-package atmospheres, and their interactions on the growth of Salmonella Typhimurium, mesophilic aerobic bacteria, yeast and mold, and the physico-chemical quality of diced onions to determine the best sanitizer and in-package atmosphere combination for both safety and quality. Diced onions were inoculated or not with S. Typhimurium, sanitized in sodium hypochlorite, peroxyacetic acid, or liquid chlorine dioxide, and then packaged in either polylactic acid bags containing superatmospheric O2, elevated CO2/reduced O2, or air, or in polyethylene terephthalate snap-fit containers. Throughout 14days of storage at 7°C, packaged diced onions were assessed for their safety (S. Typhimurium), and quality (mesophilic aerobic bacteria, yeasts and molds, physico-chemical analyses, and descriptive and consumer acceptance sensory panels). While sanitizer affected (P<0.05) fewer parameters (S. Typhimurium, mesophiles, yeasts and molds, headspace CO2, weight loss, and pH), in-package atmosphere had a significant (P<0.05) effect on all parameters evaluated. Two-way interactions between sanitizer and atmosphere that affected S. Typhimurium and pH were identified whereas 3-way interactions (sanitizer, atmosphere and time) were only observed for headspace CO2. Sodium hypochlorite and elevated CO2/reduced O2 was the best sanitizer and in-package atmosphere combination for enhancing the safety and quality of packaged diced onions. In addition, this combination led to diced onions acceptable for purchase after 2weeks of storage by trained and consumer panels.
Brick cheese was made by the washedcurd procedure from pasteurized whole milk inoculated to conta... more Brick cheese was made by the washedcurd procedure from pasteurized whole milk inoculated to contain ca. 1 x 102 to 1 x 103 Listeria monocytogenes [strain Scott A, Ohio, V7, or California]/ml. Cheeses were ripened (15°C/95% relative humidity) with a surface smear for 2, 3, or 4 wk to simulate production of mild, aged, or "Limburger-like" brick cheese, respectively, and then stored an additional 20 to 22 wk at 10°C. Populations of strains Scott A, Ohio, V7, and California increased 1.89, 1.72, .83, and .86 orders of magnitude, respectively, following completion of brining ca. 32 h after the start of cheese making. All four L. monocytogenes strains leached from cheese into brine during 24 h and survived in brine at 10*C at least 5 d after removal of cheese. Strains Scott A and Ohio grew rapidly during the initial 2 wk of smear development and attained maximum populations of ca. 6.6 and 6.2, 7.0 and 6.9, and 5.6 and 5.1 logl0/g in 4-wkold slice (pH 6.0 to 6.5), surface (pH 6.5 to 6.9), and interior (pH 5.6 to 6.2) samples of cheese, respectively. Numbers of strains Scott A and Ohio generally decreased 1-to 7-fold during 20 to 22 wk at 10°C. Strains V7 and California failed to grow appreciably in any cheese during or after smear development, despite pH of 6.8 to 7.4 in fully ripened cheese; the strains were never isolated from 2-and 3wk-old cheese and with direct plating were detected sporadically at levels gen
Duplicate lots of cold-pack cheese food were manufactured, according to nine different formulatio... more Duplicate lots of cold-pack cheese food were manufactured, according to nine different formulations, inoculated to contain ca. 5 x 102 Listeria monocytogenes (strains Scott A, V7, California or Ohio) colony forming units (CFU)/g and stored at 4°C. L. monocytogenes in cheese food was enumerated by surface-plating appropriate dilutions made in tryptose broth containing 2% (w/v) sodium citrate (TBC) on McBride Listeria Agar (MLA). Initial TBC dilutions were stored at 3°C and surface-plated on MLA after 2, 4, 6 and 8 weeks if the organism was not quantitated by direct plating of the original samples. Selected Listeria colonies were confirmed biochemically. Populations of L. monocytogenes in cheese food manufactured without preservatives or acidifying agents generally decreased less than 10-fold after 182 d of storage. However, numbers of L. monocytogenes steadily decreased in cheese food containing 0.30% sorbic acid or 0.30% sodium propionate and which was acidified to pH 5.0 to 5.1 with lactic and/or acetic acid. In cheese food preserved with 0.30% sorbic acid, L. monocytogenes survived an average of 130 d in non-acidified cheese food and 112, 93 or 74 d in cheese food acidified with lactic acid, lactic plus acetic acid, or acetic acid, respectively. When 0.30% sodium propionate was substituted for sorbic acid, L. monocytogenes survived an average of 142 d in non-acidified cheese food and 118, 103 or 98 d in cheese food acidified with lactic, acetic, or lactic plus acetic acid, respectively. Since 1983, at least 150 cases of listeriosis, including 54 deaths, resulted from consumption of pasteurized milk (17) and Mexican-style cheese (20) contaminated with Listeria monocytogenes. Recently, another outbreak reported in Switzerland resulted from consumption of Vacherin Mont d'Or soft-ripened cheese (13) and caused at least 10 cases of listeriosis, including two deaths. Increased surveillance of the dairy industry by the Food and Drug Administration, prompted by outbreaks of listeriosis associated with dairy products, has lead to isolation of L. monocytogenes from a variety of domestic cheeses including Liederkranz (2,3), Mexican-style (1,7), Ricotta (22) and Cheddar (22), as well as Brie (4,5,6,9), semi-soft (8) and soft-ripened cheese (8) imported from France. When these findings are considered along with numerous isolations of L. monocytogenes from the dairy factory environment, clearly, this organism poses a serious threat to the cheese industry. Cold-pack cheese food is defined by regulation with a Standard of Identity; Title 21, part 133.124. (18). Several dairy ingredients used in the manufacture of cold-pack cheese food, i.e. Cheddar cheese, nonfat dry milk, and dried whey, could serve as vehicles for contamination of the finished product with L. monocytogenes. Currently, Cheddar cheese manufactured from raw milk can be used in cold-pack cheese food if the cheese is ripened at > 35 °F (1.7°C) for > 60 d to eliminate pathogenic organisms (18). However, experimental evidence has shown that L. monocytogenes can survive as long as 434 d in Cheddar cheese ripened under these conditions (25). In addition, a recall because of contamination with L. monocytogenes was recently issued for raw milk Cheddar cheese which was properly ripened (22). Another study (75) showed that L. monocytogenes can survive as long as 84 d in nonfat dry milk manufactured from pasteurized skim milk inoculated to contain ca. 105 colony forming units (CFU)/ml. Ryser and Marth (26) demonstrated that L. monocytogenes can grow to levels of ca. 108 CFU/ml in filter-sterilized whey. Based on these results, the pathogen would likely survive during spray-drying of fluid whey. Recently, salted (1.2 and 2.5% NaCl) and unsalted butter were manufactured from pasteurized cream inoculated to contain ca. 104 to 105 L. monocytogenes strain Scott A CFU/g (28). After 70 d of storage at-18, 4 and 13°C, the organism was present at levels of 3.22, 5.26 and 5.84 logio CFU/g of butter, respectively. Although L. monocytogenes has yet to be isolated from commercially produced cold-pack cheese food, ingredients used to manufacture this product are clearly capable of harboring the bacterium. The presence of L. monocytogenes in coldpack cheese food is of special concern since this product receives no further heat treatment or aging and is normally consumed shortly after manufacture. Recent recalls of Lwfen'a-contaminated cheeses have
Cottage cheese was made by the short-set procedure in pilotplant-sized vats from pasteurized skim... more Cottage cheese was made by the short-set procedure in pilotplant-sized vats from pasteurized skim milk inoculated to contain 10 4-10 5 Listeria monocytogenes (strains Scott A or V7)/ ml. Half the curd from each trial (two trials with each strain of L. monocytogenes) was creamed and half remained uncreamed. Numbers of L. monocytogenes were determined by surface-plating samples diluted in Tryptose Broth (TB) on McBride's Listeria Agar (MLA). Initial TB dilutions were then stored at 3°C and plated on MLA after 2, 4, 6 and 8 weeks or until L. monocytogenes was recovered. Selected L. monocytogenes colonies from each sample were serologically confirmed. Results for both strains indicate that during manufacture, numbers of L. monocytogenes remained relatively constant until after cooking of curd was completed. All samples analyzed after cooking curd 30 min at 57.2°C (135°F) contained fewer viable L. monocytogenes than could be detected by our methods (10 or 100 CFU/g or ml). Both strains were recovered from cold-enrichment samples, indicating that small numbers of the organism survived the cheesemaking process. Using direct plating onto MLA, L. monocytogenes was recovered from 43 of 112 (38.4%) cottage cheese samples during storage at 3°C for up to 28 d. After cold-enrichment in TB for up to 8 weeks, 59 of 112 (52.7%) samples were positive forL. monocytogenes. Greater numbers of L. monocytogenes, particularly strain Scott A, were found in creamed rather than uncreamed cottage cheese; however, numbers seldom exceeded 100/g. Listeria monocytogenes is a potential foodborne pathogen which can cause abortions in pregnant women and meningitis or meningio-encephalitis in immunocompromised men and women (6,13,14). In dairy cattle, L. monocytogenes can cause mastitis and abortion, leading to excretion of the organism in milk from the infected animal (4,5,15). Evidence for the role of milk in transmission of L. monocytogenes from infected dairy cattle to man has appeared in European literature. The first reported massive outbreak of human listeriosis occurred in Halle, Germany and was followed by epidemics in Jena, Germany and Prague, Czechoslovakia (14). Consumption of Listeriacontaminated raw milk was believed to be the cause of human illness.
ABSTRACT Microbial challenge studies using nonpathogenic surrogates provide a practical means for... more ABSTRACT Microbial challenge studies using nonpathogenic surrogates provide a practical means for validating thermally based pathogen controls for low-moisture foods. Because the relative thermal resistance, or kill ratio, of Enterococcus faecium NRRL B-2354 (a nonpathogenic surrogate) to Salmonella is greatly influenced by food composition, this study assessed relative thermal resistance of a five-strain Salmonella cocktail and E. faecium in skim milk powder (SMP), lactose-free skim milk powder (LSMP), 90% milk protein isolate (MPI), and lactose powder (LP). The impact of sugar composition (lactose versus glucose-galactose) on resuscitation of bacterial survivors, by using SMP and LSMP, was also determined. Dairy powders were inoculated with agar-grown cultures, mixed, preequilibrated at 0.25 water activity (aw), ground to achieve homogeneity, reequilibrated, and subjected to isothermal treatment. After enumeration on nonselective differential media, log-linear and Bigelow models were fit to the survivor data via one-step global regression. The aw changes and glass transition temperature were assessed at elevated temperatures by using uninoculated, equilibrated powder samples. Estimated D90°C-values were approximately two times higher for E. faecium (P < 0.05) than for Salmonella in SMP, LP, and MPI, but statistically similar (P > 0.05) in LSMP. Addition of sugars to recovery media did not influence survivor resuscitation from heat-treated SMP and LSMP, confirming that microbial inactivation was impacted primarily by the thermal treatment, not the recovery step. Thermally induced changes in aw were seen only for LP and MPI, with the glass transition temperature observed only for SMP and MPI. In conclusion, rather than always requiring greater lethality of E. faecium than Salmonella, these findings suggest that sufficient pathogen controls for low-moisture foods can also be validated by thoroughly documenting the appropriate kill ratios of E. faecium to Salmonella. HIGHLIGHTS
ABSTRACT Use of silver nanoparticles (Ag NPs) in pesticides may lead to residual levels in food c... more ABSTRACT Use of silver nanoparticles (Ag NPs) in pesticides may lead to residual levels in food crops, thus raising food safety and environmental concerns. Because little is known about Ag NP behavior in wash water during typical commercial washing of fresh produce, this study assessed the temporal changes in Ag NP behavior when exposed to 2 to 100 mg/L free chlorine (Cl2) in simulated lettuce wash water for up to 10 days. Aggregate size and zeta potential of Ag NPs (5 mg/L) were evaluated in the presence and absence of dissolved lettuce extract (DLE, 0.1%), with Ag NPs in deionized water serving as the control treatment. In the presence of chlorine, greater aggregation of Ag NPs occurred over time (49 to 431 nm) compared with the control treatment (P < 0.05). Lower zeta potentials (−39 to −95 mV) were observed in the chlorine-only treatments, likely due to the formation of AgCl particles. Larger aggregates and lower zeta potentials were also observed in DLE (84 to 273 nm and −28 to −32 mV, respectively), as compared with the control treatment. After 7 to 10 days, larger aggregates were seen in the chlorine-only treatments as compared with the DLE treatments, despite lower zeta potentials, probably facilitated by nucleation and crystal growth of AgCl. Transmission electron microscopy with energy dispersive spectroscopy confirmed the formation of AgCl-Ag NP composite particles with chlorine and the embedding of AgCl and Ag NPs in the DLE matrix. Thus, DLE might stabilize and protect Ag NPs from chlorine. These findings indicate that chlorine and plant-released organic material can substantially change the behavior of Ag NPs, which may, in turn, impact both removal from fresh-cut produce during washing and their environmental fate. HIGHLIGHTS
Recent work by epidemiologists and microbiologists has uncovered several hitherto unrecognized fo... more Recent work by epidemiologists and microbiologists has uncovered several hitherto unrecognized food-borne bacterial pathogens of public health significance. One of these, Listeria monocytogenes, has attracted considerable attention because of two major cheese-related outbreaks of listeriosis that were characterized by cases of meningitis, abortion, and perinatal septicemia. Thus far, L. monocytogenes has been responsible for well over 300 reported cases of food-borne listeriosis, including about 100 deaths, and has cost the dairy industry alone more than 66 million dollars as a result of product recalls. The ability of L. monocytogenes to grow at refrigeration temperatures, coupled with appearance of the pathogen in raw and processed meats, as well as poultry, vegetables, and seafood, makes this bacterium a serious threat to susceptible consumers and to the entire food industry. Yersinia enterocolitica, another psychrotrophic food-borne pathogen of recent concern, was linked to several outbreaks of yersiniosis associated with consumption of both raw and pasteurized milk, as well as contaminated water. Food-borne infections involving Y. enterocolitica typically result in enterocolitis, which may be mistaken for acute appendicitis. Unfortunately, inadvertent removal of healthy appendixes from victims of food-borne yersiniosis is all too common. Although known for many years, Campylobacter jejuni has only recently been recognized as a food-borne pathogen and a leading cause of gastroenteritis in the United States. Notable outbreaks of campylobacteriosis linked to consumption of raw milk, cake icing, eggs, poultry, and beef have underscored the need for thorough cooking and proper handling of raw products.(ABSTRACT TRUNCATED AT 250 WORDS)
Listeria monocytogenes first emerged as a serious threat to the dairy industry in 1985 when a maj... more Listeria monocytogenes first emerged as a serious threat to the dairy industry in 1985 when a major outbreak of listeriosis was traced to consumption of soft Mexican-style cheese in southern California, with other dairy-related outbreaks primarily involving pasteurized milk and certain soft cheeses prepared from raw milk having since been reported. Listeria monocytogenes causes abortion and perinatal septicemia in pregnant women and meningitis in the elderly and immunocompromised patients; it can also produce clinical and subclinical mastitis in ruminant animals, with about 2.5–5% of the raw milk supply found positive for this pathogen. Listeria monocytogenes is endemic to dairy farms and to a lesser extent dairy processing facilities where this pathogen is typically considered a postpasteurization contaminant. Unlike many other bacterial foodborne pathogens, L. monocytogenes can grow in milk at refrigeration temperatures and reach potentially infectious levels in certain high-moisture and surface-ripened cheeses. However, barring postpasteurization contamination, properly pasteurized fluid milk products will be free of Listeria.
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Papers by Elliot Ryser