J. Med. Microbiol. — Vol. 51 (2002), 399–404
# 2002 Society for General Microbiology
ISSN 0022-2615
MOLECULAR EPIDEMIOLOGY
Subtype distribution of Haemophilus influenzae
isolates from North India
A. SHARMA, R. KAUR, N. K. GANGULY, P. D. SINGH and A. CHAKRABORTI
Department of Experimental Medicine and Biotechnology, Postgraduate Institute of Medical Education and
Research, Chandigarh, India
A total of 120 Haemophilus influenzae isolates from blood, cerebrospinal fluid, sputum
and throat swabs of patients and carriers in North India was characterised by biotyping,
ribotyping and random amplification of polymorphic DNA (RAPD)-PCR. Of these, 77
isolates (64%) were serotype b; the other 43 (36%) were non-typable. Biotype I was the
most predominant among the typable strains and biotype II among the non-typable
strains. Ribotyping with restriction endonucleases HaeIII and EcoRI differentiated the
isolates into three and six ribotypes, respectively. However, RAPD fingerprints generated
by the application of arbitrary primers AP1 and AP2 provided a higher level of
discrimination. RAPD typing revealed distinct polymorphism among the serologically
typable isolates. This study is the first report that stratifies the subtypes of H. influenzae
strains from India by molecular techniques.
Introduction
Haemophilus influenzae, although a common commensal of the upper respiratory tract of healthy individuals
[1], is an important pathogen. The species is divided
into six capsular types on the basis of production of a
polysaccharide capsule [2] of which type b is a
frequent cause of meningitis and other invasive
disorders in children [3]. The non-capsulate strains
also cause a wide spectrum of clinical infections
including chronic bronchitis, pneumonia and bacteraemia, and are found in 75% of healthy individuals [4].
In India, 96% of all haemophilus infections are caused
by H. influenzae serotype b (Hib) [5]. Since the mid1950s, Hib has been the most common cause of
pyogenic meningitis in children in India. The burden of
invasive Hib is substantial, with the incidence of Hib
meningitis estimated to be 50–60 cases=100 000 children ,5 years of age [6]. A study from Delhi has also
reported Hib to be a common cause of pneumonia in
19% of cases in children [7]. The outcome has not
changed significantly in the past decade despite the
introduction of potent antibiotics.
strains circulating in the community has been documented previously [8]. Therefore, the availability of
high resolution typing assays is a prerequisite for the
study of H. influenzae epidemiology. The investigation
and comparison of outbreaks of infection have been
hampered by the lack of standardised, highly discriminatory methods for characterising the strains. The use
of several molecular typing techniques for the effective
detection of outbreaks of infection as well as identification of new and infectious clones of H. influenzae
has been reported in recent years [9, 10]. Among these,
restriction fragment length polymorphism analysis with
ribosomal RNA (rRNA) as the probe [11–13] has been
used widely to differentiate isolates into ribotypes.
Intra-specific genetic variation can also be detected by
randomly amplified polymorphic DNA (RAPD) analysis. In RAPD, the amplicons, when arrayed by
electrophoresis, yield fingerprints which differ depending on the relatedness of the genomic templates [14].
The aim of this study was to characterise the H.
influenzae isolates from patients and carriers by biotyping, ribotyping and RAPD fingerprinting and thus to
analyse the subtype distribution of isolates from India.
The large and genetically diverse pool of H. influenzae
Materials and methods
Received 7 Aug. 2001; revised version accepted 27 Nov.
2001.
Corresponding author: Dr A. Chakraborti (e-mail: superoxide
@sify.com).
Study population
Seventy-seven H. influenzae type b isolates from
cerebrospinal fluid (CSF) and blood samples of infants
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A. SHARMA ET AL.
(aged ,1 year) suffering from meningitis and bacteraemia, respectively, attending clinics at the Postgraduate Institute of Medical Education and Research,
Chandigarh, India, were examined. Forty-three nontypable isolates were cultured from throat swabs of
children (aged 5–15 years) and adults (aged 23–
40 years) with informed consent and from the sputum
of patients (aged 25–35 years) suffering from chronic
bronchitis. Patients with a history of antibiotic therapy
and those currently receiving antibiotics were excluded.
All the samples were collected between March 1997
and July 2000.
Bacterial isolates
The samples collected from the patients and carriers
were cultured on 7% chocolate agar in an atmosphere
containing CO2 5%. H. influenzae isolates were
identified by their typical colony morphology and
growth requirements for NAD and haemin. Serotyping
was performed by slide agglutination tests with antisera
to the capsular antigens a–f (Difco). Biotypes were
assigned by testing H. influenzae isolates for the ability
to produce urease, indole and ornithine decarboxylase
by the method of Kilian [15]. The isolates were stored
at
708C in Brain Heart Infusion Broth (Difco)
supplemented with glycerol 5% v/v.
Preparation of genomic DNA
Genomic DNA was extracted by a modification of the
method described by Pitcher et al. [16]. Briefly, the
bacterial colonies from overnight cultures were suspended in 150 l of TE buffer (10 mM Tris-HCl, 1 mM
EDTA, pH 8.0) and lysed by adding 450 l of solution
containing 5 M guanidium thiocyanate, 100 mM EDTA
and sarkosyl 0.5% v/v. After incubation at 48C for
10 min, 7.5 M cold ammonium acetate was added. The
DNA was extracted with phenol-chloroform, precipitated with ethanol and finally dissolved in TE. DNA
preparations from different samples were quantified
spectrophotometrically and stored at 208C for further
use.
RAPD fingerprinting
RAPD analysis was performed with primers (Genset,
Singapore) AP1 (59-AAG TAA GTG ACT GGG GTG
AGC G-39) and AP2 (59-ATG TAA GCT CCT GGG
GAT TCA C-39) which were arbitrarily chosen from
enterobacterial repetitive intergenic consensus sequences. PCR amplification was performed in a 25- l
volume mixture containing 100 ng of template DNA,
200 M dNTPs, 200 ng of primer and 1 unit of Taq
polymerase (Roche, Germany). The reaction mixtures
were overlaid with a drop of sterile mineral oil (Sigma)
in each PCR tube to avoid evaporation during cycling.
A negative control containing all the ingredients except
template DNA was run in parallel to each PCR
experiment. After an initial denaturation for 5 min at
948C, the PCR was performed for 35 cycles in an
automated thermal cycler (Perkin-Elmer Cetus, USA)
programmed for denaturation at 948C for 1 min,
annealing at 258C for 1 min and extension at 728C
for 4 min. The amplification reactions were repeated
three times to check the reproducibility of the RAPDPCR banding profiles. The final extension time was
10 min at 728C. The amplification products (12 l)
were electrophoresed in agarose 1% gels (FMC
Bioproducts, USA) in Tris-borate-EDTA buffer containing ethidium bromide 0.5 g=ml. These gels were
visualised in a UV transilluminator (Fotodyne, USA)
and photographed. Appropriate DNA mol. wt markers
were used for sizing the bands in the gel. Finally,
RAPD-PCR bands were interpreted by visual analysis
of the polaroid pictures.
Discriminatory power of the typing methods
The discriminatory ability of each typing method
shown in Table 2 was determined by calculating the
numerical discrimination index (DI) by the method of
Hunter and Gaston [18]. A DI of 1.0 indicates that the
typing method is able to distinguish each strain from
the test population. Conversely, a DI of 0 indicates that
all the strains of the test population are indistinguishable.
Results
Ribotyping
Genomic DNA (10 g) digested with restriction endonucleases HaeIII and EcoRI (Roche, Germany) was
separated in agarose 0.8% gel. Southern hybridisation
was performed by standard procedures [17]. The probe
used was a synthetic oligonucleotide (59-AAG AGT
TTG ATC CTG GCT CAG-39) from bacterial 16S
rRNA (Biobasics, Canada) and was prepared by endlabelling with ª32 P-ATP (BRIT, Hyderabad, India). The
membranes were hybridised with the probe, washed
and autoradiographed by exposure to X-ray film by the
method of Bruce and Jordens [9].
Genetic polymorphism of H. influenzae strains prevalent in India was studied by biotyping, ribotyping
and RAPD analysis and compared for epidemiological
purposes. The results of these typing techniques are
summarised in Table 1. A total of 305 cerebrospinal
fluid (CSF) and 41 blood samples from infants (aged
,1 year) suffering from meningitis and bacteraemia,
respectively, was screened; 73 H. influenzae serotype b
isolates were obtained from CSF and 4 from blood. The
throat swabs of 40 healthy children (aged 5–15 years)
and 23 adults (aged 23–40 years), and the sputum
samples of 25 patients (aged 25–35 years) suffering
from chronic bronchitis were also screened; 25, 10 and
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10
8
11
8
10
7
8
9
4
3
9
16
43
2
11 10
7
5
10
Type b
Non-typable
31 24 8
11 17 12
9
5
3
51 17
22
7
9
14
21
7
8
7
6 28
15 21
7
401
8 non-typable isolates were obtained from the respective groups. Seventy-seven strains (64%) were serotype
b and 43 (36%) were non-typable. A few type b strains
that were isolated from the throat swabs of a healthy
carrier population were not included in the study. Other
capsulate serotypes of H. influenzae, i.e., a, c, d, e and
f, were not observed.
Biotyping differentiated the set of isolates into six
biotypes; biotypes VI and VIII were not found (Table
1). Biotypes I, II and III were common among both the
serotype b and non-typable isolates. Biotype I was
predominant (40%) among the typable strains in the
study population, although most of the non-typable
isolates (39%) were of biotype II. Biotypes IV and V
were found only in the typable isolates while biotype
VII was associated only with the non-typable isolates.
6
i
h
g
a
f
e
a
D
C
V
VI VII VIII A
B
C
A
B
EcoRI
HaeIII
Biotype
III IV
II
I
H. influenzae
isolates
Ribotype with
Table 1. Subtype distribution of H. influenzae isolates from North India
E
F
b
c
d
AP1
g
h
i
j
b
c
d
RAPD-fingerprint with
e
f
AP2
j
10
k
8
l
17
8
m
MOLECULAR TYPING OF INDIAN H. INFLUENZAE ISOLATES
Ribotyping with HaeIII restriction endonuclease discriminated the H. influenzae isolates into three
ribotypes, each characterised by the presence of four
or five fragments of differing size ranging from 0.5 kb
to 4.4 kb (Fig. 1a). Ribotype A was the most prevalent
among both the typable (66%) and non-typable (51%)
isolates (Table 1). Ribotype analysis on digestion with
EcoRI revealed six distinct banding patterns, with band
size ranging from 0.5 to 10 kb (Fig. 1b, Table 1) of
which ribotype E was the most common among both
serotype b (36%) and non-typable (49%) isolates.
However, EcoRI restriction allowed minor differentiation among the non-typable isolates.
Intra-serotypic variation was also evident by RAPD
fingerprinting. The H. influenzae isolates exhibited
marked heterogeneity with each of the arbitrary
primers AP1 and AP2. Arrays of fragments ranging
from 0.2 kb to 1.5 kb in size were observed. All the
major and minor bands that were reproducible by
repeated experiments were scored. The serotype b
isolates showed 10 distinct banding patterns with
primer AP1 (Fig. 2a), although it did not allow any
differentiation among the non-typable isolates. RAPD
type g was the most common among the serotype b
isolates (21%) and was shown by all the non-typable
isolates (Table 1). Primer AP2 provided the highest
level of discrimination with a DI value of 0.925 (Table
2) among the isolates where variation in both number
and size of bands could be observed in the fingerprints
(Fig. 2b). Each of the RAPD patterns of the nontypable isolates was distinct from those of the type b
isolates. AP2 could also differentiate the non-typable
isolates that showed similar profiles with AP1. Therefore, AP2 was found to be more discriminatory than
primer AP1 (Table 2).
Among the typable H. influenzae isolates from blood,
there was complete concordance between ribotyping
with EcoRI and RAPD fingerprinting with both the
primers. Three of the four isolates from blood were of
ribotype A with EcoRI and RAPD type a with AP1 and
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A. SHARMA ET AL.
Fig. 1. Genomic ribotyping pattern of different subtypes of H. influenzae isolates following restriction enzyme digestion with (a)
HaeIII, (b) EcoRI. Numbers indicate the molecular size corresponding to the marker (º DNA, digested with HindIII).
Fig. 2. RAPD-PCR amplification pattern of different subtypes of H. influenzae isolates with (a) AP1 primer, (b) AP2 primer. M,
DNA molecular size marker.
Table 2. Discrimination indices [18] for the typing
methods for H. influenzae
Typing method
Biotyping
Ribotyping with HaeIII
Ribotyping with EcoRI
RAPD fingerprinting with AP1
RAPD fingerprinting with AP2
Number of Discrimination index
types
(DI)
6
3
6
10
13
0.731
0.558
0.743
0.729
0.925
AP2 whereas one isolate was of ribotype D and RAPD
type d, respectively. All these four isolates belonged to
ribotype A on digestion with HaeIII. Six of the isolates
from the CSF samples belonged to ribotype A with the
enzymes (EcoRI and HaeIII) and RAPD type a with
both the primers and hence gave concordant profiles
with all four genotyping methods.
Among the non-typable isolates, all eight isolates from
the sputum samples of patients with chronic bronchitis
showed complete concordance with HaeIII ribotyping
and RAPD analysis with both the primer sets. These
samples showed ribotype A with HaeIII and RAPD
type g and k with primers AP1 and AP2, respectively.
EcoRI digestion further differentiated five of these
isolates into ribotype A and three into ribotype E.
However, the non-typable isolates from the throat
swabs of the healthy carrier population demonstrated
discordant results and were randomly distributed over
the various subtypes.
Discussion
H. influenzae causes a wide spectrum of conditions that
range from asymptomatic colonisation of the upper
respiratory tract to serious infections such as meningitis. H. influenzae type b is a leading cause of bacterial
meningitis and other invasive infections in childhood
world-wide. In India, the annual incidence of Hib
meningitis has been quite high and results in severe
morbidity and mortality in children ,5 years of age
[5, 6]. In the present investigation also, 24% (73 of a
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MOLECULAR TYPING OF INDIAN H. INFLUENZAE ISOLATES
403
total 305) of the CSF and 10% (4 of 41) of the total
blood samples screened were found to be positive for
H. influenzae serotype b, which indicates a high
prevalence of Hib-associated meningitis. Despite early
diagnosis and appropriate treatment, Hib infection has
been difficult to control and continues to pose an
extensive health burden. Hence, there is an urgent need
to study the epidemiology of H. influenzae in this
community.
RAPD analysis of these strains showed two distinct
patterns that were biotype-specific [27]. In the present
study, the ribotypes obtained with HaeIII restriction
endonuclease generated three banding profiles and were
almost similar for the typable and non-typable isolates.
Highly polymorphic bands were observed among the
typable isolates with EcoRI, although non-typable
isolates did not reveal much heterogeneity (Fig. 1,
Table 1).
The ability to detect more subtle variations has
increased substantially with the development of highly
sensitive molecular techniques [9, 10]. Ribotyping [19]
and RAPD-PCR [20, 21] have been used for detecting
polymorphism within medically important organisms.
However, the value of any typing procedure depends on
the discriminatory power of the particular technique
being applied.
In the present study, the arbitrary primers AP1 and AP2
used for RAPD analysis are from the enterobacterial
repetitive intergenic consensus sequences. These sequences are highly conserved and are able to show
discrimination in many other organisms [33, 34]. In the
present study, variations within the typable strains were
observed by AP1 primer PCR fingerprinting. However,
the non-typable H. influenzae demonstrated no differentiation with this primer. Primer AP2 was found to be
more discriminatory and was able to show variations
even within the serologically non-typable strains.
Genotypic typing of the Indian H. influenzae isolates
showed a high DI value by RAPD fingerprinting.
Subtyping of H. influenzae by protein analysis has been
done with strains from North America, Europe and UK
[22, 23]. Molecular studies have also been done with
these strains [24, 25] and also with Australian [26] and
Japanese strains [27]. However, there has been a dearth
of data on molecular analysis of strains from India.
Hence we have, for the first time, subtyped H.
influenzae isolates from India by genotypic methods.
In the USA, .95% of invasive H. influenzae are of
serotype b and biotype I [28, 29]. In Western Europe,
only biotypes I and II are prevalent in most countries
although biotypes III, IV and V have also been detected
[30]. In Japan, 73% of Hib strains belong to biotype I,
20% to biotype II and the remainder to biotype III.
Serotypes a and c (found occasionally) are associated
with biotypes I and I or IV, respectively, while the
serologically non-typable isolates are distributed among
all the eight biotypes, predominantly biotypes II and III
[31]. In developing countries, 70–80% of H. influenzae
strains are of serotype b. In a study from Pakistan, 64%
of the samples screened were of serotype b and 98% of
them belonged to biotype II [32]. However, in the
present study, biotype I was the most predominant
among the Hib strains, followed by biotype II among
the serologically non-typable isolates. Interestingly,
biotypes VI and VIII were not found in the population.
The data further reveal concordance of profiles with the
isolates from blood, sputum and a few of the CSF
samples from the respective patient groups by both
ribotyping and RAPD-fingerprinting. This was in
contrast to isolates from normal individuals, which
presented random profiles.
In conclusion, the ability to identify strain variants
appearing during persistent H. influenzae infections
indicates that RAPD-fingerprinting is suitable for
revealing genotypic diversity within serotypes. This
typing method may be useful in the investigation of
outbreaks of infection as it is quick to perform,
requires modest effort and no previous genetic knowledge of the target organism is needed.
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