Pseudomonas aeruginosa is an opportunistic human pathogen that causes severe, life threatening in... more Pseudomonas aeruginosa is an opportunistic human pathogen that causes severe, life threatening infections in patients with cystic fibrosis (CF), endocarditis, wounds, or with artificial implants. During CF pulmonary infections, P. aeruginosa often encounters environments where the levels of calcium (Ca(2+)) are elevated. Previously, we showed that P. aeruginosa responds to externally added Ca(2+) through enhanced biofilm formation, increased production of several secreted virulence factors, and by developing a transient increase in the intracellular Ca(2+) followed by its removal to the basal sub-micromolar level. However, the molecular mechanisms responsible for regulating Ca(2+)-induced virulence factor production and Ca(2+) homeostasis are not known. Here, we characterized the genome-wide transcriptional response of P. aeruginosa to elevated [Ca(2+)] in both planktonic cultures and in biofilms. Among the genes induced by CaCl2 in strain PAO1 was an operon containing the two-component regulator PA2656-PA2657 (here called carS and carR), while the closely related two-component regulators, phoPQ and pmrAB, were repressed by CaCl2 addition. To identify the regulatory targets of CarSR, we constructed a deletion mutant of carR, and performed transcriptome analysis of the mutant strain at low and high [Ca(2+)]. Among the genes regulated by CarSR in response to CaCl2 are the predicted periplasmic OB-fold protein, PA0320 (here called carO) and the inner membrane-anchored five-bladed β-propeller protein, PA0327 (here called carP). Mutations in both carO and carP affected Ca(2+) homeostasis, reducing the ability of P. aeruginosa to export excess Ca(2+). In addition, a mutation in carP had a pleotropic effect in a Ca(2+)-dependent manner, altering swarming motility, pyocyanin production, and tobramycin sensitivity. Overall, the results indicate that the two-component system CarSR is responsible for sensing high levels of external Ca(2+), and responding through its regulatory targets that modulate Ca(2+) homeostasis, surface-associated motility, and production of the virulence factor, pyocyanin. During infectious disease, Pseudomonas aeruginosa encounters environments with high calcium (Ca(2+)) concentration, yet the cells maintain intracellular Ca(2+) at levels that are orders of magnitude less than the external environment. In addition, Ca(2+) signals P. aeruginosa to induce production of several virulence factors. Compared to eukaryotes, little is known about how bacteria maintain Ca(2+) homeostasis, or how Ca(2+) acts as a signal. In this study, we identified a two-component regulatory system in P. aeruginosa PAO1, termed CarRS, that is induced at elevated Ca(2+). CarRS modulates Ca(2+) signaling and Ca(2+) homeostasis through its regulatory targets, CarO and CarP. The results demonstrate that P. aeruginosa uses a two-component regulatory system to sense external Ca(2+), and relays that information for Ca(2+)-dependent cellular processes.
Listeriosis is a serious foodborne infection that disproportionately affects elderly adults, preg... more Listeriosis is a serious foodborne infection that disproportionately affects elderly adults, pregnant women, newborns, and immunocompromised individuals. Diagnosis is made by culturing Listeria monocytogenes from sterile body fluids or products of conception. This report describes investigations of two listeriosis pseudo-outbreaks caused by contaminated laboratory media made from sheep blood.
INTRODUCTIONThe metabolic activities of bacteria growing in biofilms result in spatial gradients ... more INTRODUCTIONThe metabolic activities of bacteria growing in biofilms result in spatial gradients of oxygen, nutrients, and waste products. Because bacteria respond to local environmental conditions through changes in gene expression, mRNA levels of individual genes may vary spatially among bacteria within the biofilm. This article describes an approach to isolate RNA for quantification from cells at localized sites within biofilms. Biofilm thin sections are generated by embedding biofilms in cryoembedding resin, freezing the embedded biofilms on dry ice, and cutting with a cryomicrotome. The sections are placed on membrane-coated microscope slides and maintained on dry ice. Laser capture microdissection microscopy (LCMM) is used to dissect small subsets of cells at different regions within the biofilms, and RNA is extracted from the samples using either hot phenol or TRI reagent. A TRI reagent-based DNA extraction method is also presented.
INTRODUCTIONBacteria growing in biofilms often express a different subset of genes compared to th... more INTRODUCTIONBacteria growing in biofilms often express a different subset of genes compared to the same strains growing planktonically. Quantitative reverse transcriptase real time PCR (qRT-PCR) can be used effectively to quantify the number of RNA transcripts of specific genes from bacteria growing in biofilms. qRT-PCR has a large dynamic range and may be used to verify gene expression data obtained from microarrays. In addition, qRT-PCR is sensitive, and therefore may be used to quantify gene expression from biofilm samples where only a small amount of biological material is available, as in samples obtained by laser capture microdissection microscopy (LCMM). The most commonly used qRT-PCR methods are the SYBR Green and dual-labeled probe (Taqman) approaches. Both approaches use reverse transcription to convert mRNA to cDNA, followed by PCR amplification of the cDNA. This article describes steps involved in aspects of qRT-PCR including (1) primer design, (2) primer and probe performance testing, (3) qRT-PCR using the Corbett Rotor-Gene system, and (4) data export and analysis.
In this study, a multicenter evaluation of the Life Technologies TaqMan(®) Array Card (TAC) with ... more In this study, a multicenter evaluation of the Life Technologies TaqMan(®) Array Card (TAC) with 21 custom viral and bacterial respiratory assays was performed on the Applied Biosystems ViiA™ 7 Real-Time PCR System. The goal of the study was to demonstrate the analytical performance of this platform when compared to identical individual pathogen specific laboratory developed tests (LDTs) designed at the Centers for Disease Control and Prevention (CDC), equivalent LDTs provided by state public health laboratories, or to three different commercial multi-respiratory panels. CDC and Association of Public Health Laboratories (APHL) LDTs had similar analytical sensitivities for viral pathogens, while several of the bacterial pathogen APHL LDTs demonstrated sensitivities one log higher than the corresponding CDC LDT. When compared to CDC LDTs, TAC assays were generally one to two logs less sensitive depending on the site performing the analysis. Finally, TAC assays were generally more sensitive than their counterparts in three different commercial multi-respiratory panels. TAC technology allows users to spot customized assays and design TAC layout, simplify assay setup, conserve specimen, dramatically reduce contamination potential, and as demonstrated in this study, analyze multiple samples in parallel with good reproducibility between instruments and operators.
Pseudomonas aeruginosa is an opportunistic human pathogen that causes severe, life threatening in... more Pseudomonas aeruginosa is an opportunistic human pathogen that causes severe, life threatening infections in patients with cystic fibrosis (CF), endocarditis, wounds, or with artificial implants. During CF pulmonary infections, P. aeruginosa often encounters environments where the levels of calcium (Ca(2+)) are elevated. Previously, we showed that P. aeruginosa responds to externally added Ca(2+) through enhanced biofilm formation, increased production of several secreted virulence factors, and by developing a transient increase in the intracellular Ca(2+) followed by its removal to the basal sub-micromolar level. However, the molecular mechanisms responsible for regulating Ca(2+)-induced virulence factor production and Ca(2+) homeostasis are not known. Here, we characterized the genome-wide transcriptional response of P. aeruginosa to elevated [Ca(2+)] in both planktonic cultures and in biofilms. Among the genes induced by CaCl2 in strain PAO1 was an operon containing the two-component regulator PA2656-PA2657 (here called carS and carR), while the closely related two-component regulators, phoPQ and pmrAB, were repressed by CaCl2 addition. To identify the regulatory targets of CarSR, we constructed a deletion mutant of carR, and performed transcriptome analysis of the mutant strain at low and high [Ca(2+)]. Among the genes regulated by CarSR in response to CaCl2 are the predicted periplasmic OB-fold protein, PA0320 (here called carO) and the inner membrane-anchored five-bladed β-propeller protein, PA0327 (here called carP). Mutations in both carO and carP affected Ca(2+) homeostasis, reducing the ability of P. aeruginosa to export excess Ca(2+). In addition, a mutation in carP had a pleotropic effect in a Ca(2+)-dependent manner, altering swarming motility, pyocyanin production, and tobramycin sensitivity. Overall, the results indicate that the two-component system CarSR is responsible for sensing high levels of external Ca(2+), and responding through its regulatory targets that modulate Ca(2+) homeostasis, surface-associated motility, and production of the virulence factor, pyocyanin. During infectious disease, Pseudomonas aeruginosa encounters environments with high calcium (Ca(2+)) concentration, yet the cells maintain intracellular Ca(2+) at levels that are orders of magnitude less than the external environment. In addition, Ca(2+) signals P. aeruginosa to induce production of several virulence factors. Compared to eukaryotes, little is known about how bacteria maintain Ca(2+) homeostasis, or how Ca(2+) acts as a signal. In this study, we identified a two-component regulatory system in P. aeruginosa PAO1, termed CarRS, that is induced at elevated Ca(2+). CarRS modulates Ca(2+) signaling and Ca(2+) homeostasis through its regulatory targets, CarO and CarP. The results demonstrate that P. aeruginosa uses a two-component regulatory system to sense external Ca(2+), and relays that information for Ca(2+)-dependent cellular processes.
Listeriosis is a serious foodborne infection that disproportionately affects elderly adults, preg... more Listeriosis is a serious foodborne infection that disproportionately affects elderly adults, pregnant women, newborns, and immunocompromised individuals. Diagnosis is made by culturing Listeria monocytogenes from sterile body fluids or products of conception. This report describes investigations of two listeriosis pseudo-outbreaks caused by contaminated laboratory media made from sheep blood.
INTRODUCTIONThe metabolic activities of bacteria growing in biofilms result in spatial gradients ... more INTRODUCTIONThe metabolic activities of bacteria growing in biofilms result in spatial gradients of oxygen, nutrients, and waste products. Because bacteria respond to local environmental conditions through changes in gene expression, mRNA levels of individual genes may vary spatially among bacteria within the biofilm. This article describes an approach to isolate RNA for quantification from cells at localized sites within biofilms. Biofilm thin sections are generated by embedding biofilms in cryoembedding resin, freezing the embedded biofilms on dry ice, and cutting with a cryomicrotome. The sections are placed on membrane-coated microscope slides and maintained on dry ice. Laser capture microdissection microscopy (LCMM) is used to dissect small subsets of cells at different regions within the biofilms, and RNA is extracted from the samples using either hot phenol or TRI reagent. A TRI reagent-based DNA extraction method is also presented.
INTRODUCTIONBacteria growing in biofilms often express a different subset of genes compared to th... more INTRODUCTIONBacteria growing in biofilms often express a different subset of genes compared to the same strains growing planktonically. Quantitative reverse transcriptase real time PCR (qRT-PCR) can be used effectively to quantify the number of RNA transcripts of specific genes from bacteria growing in biofilms. qRT-PCR has a large dynamic range and may be used to verify gene expression data obtained from microarrays. In addition, qRT-PCR is sensitive, and therefore may be used to quantify gene expression from biofilm samples where only a small amount of biological material is available, as in samples obtained by laser capture microdissection microscopy (LCMM). The most commonly used qRT-PCR methods are the SYBR Green and dual-labeled probe (Taqman) approaches. Both approaches use reverse transcription to convert mRNA to cDNA, followed by PCR amplification of the cDNA. This article describes steps involved in aspects of qRT-PCR including (1) primer design, (2) primer and probe performance testing, (3) qRT-PCR using the Corbett Rotor-Gene system, and (4) data export and analysis.
In this study, a multicenter evaluation of the Life Technologies TaqMan(®) Array Card (TAC) with ... more In this study, a multicenter evaluation of the Life Technologies TaqMan(®) Array Card (TAC) with 21 custom viral and bacterial respiratory assays was performed on the Applied Biosystems ViiA™ 7 Real-Time PCR System. The goal of the study was to demonstrate the analytical performance of this platform when compared to identical individual pathogen specific laboratory developed tests (LDTs) designed at the Centers for Disease Control and Prevention (CDC), equivalent LDTs provided by state public health laboratories, or to three different commercial multi-respiratory panels. CDC and Association of Public Health Laboratories (APHL) LDTs had similar analytical sensitivities for viral pathogens, while several of the bacterial pathogen APHL LDTs demonstrated sensitivities one log higher than the corresponding CDC LDT. When compared to CDC LDTs, TAC assays were generally one to two logs less sensitive depending on the site performing the analysis. Finally, TAC assays were generally more sensitive than their counterparts in three different commercial multi-respiratory panels. TAC technology allows users to spot customized assays and design TAC layout, simplify assay setup, conserve specimen, dramatically reduce contamination potential, and as demonstrated in this study, analyze multiple samples in parallel with good reproducibility between instruments and operators.
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