Download Role of host genetic factors in susceptibility to group A streptococcal

Indian J Med Res 119 (Suppl) May 2004, pp 141-143
Role of host genetic factors in susceptibility to group A streptococcal
infections
Oliver Goldmann, Gursharan S. Chhatwal & Eva Medina
Division of Microbiology, Department of Microbial Pathogenesis & Vaccine Research,
GBF-National Research Centre for Biotechnology, Braunschweig, Germany
Received August 7, 2003
Background & objectives: Epidemiological evidences indicate that host genetic factors might be critical
in determining susceptibility to infection with group A streptococci (GAS). The objective of the present
study was to determine the extent to which the genetic background of the mouse strain affected
induction and resolution of GAS infection.
Methods: Several inbred mouse strains were intravenously infected with Streptococcus pyogenes strain
A20 and the mean survival times of mice was recorded overtime. Bacterial loads were determined in
liver and spleen of infected animals at 48 h postinoculation.
Results: Different strains of mice exhibited differential susceptibility to GAS infection. After systemic
infection with S. pyogenes, inbred mice showed substantial differences in mortality and bacterial
loads.
Interpretation & conclusion: This study provides further evidences that a genetic component is associated
with host susceptibility or resistance to GAS infection.
Key words GAS - host genetic factors - infection - susceptibility
Group A streptococci (GAS) infections have a wide
spectrum of clinical presentations ranging from mild, selflimiting infections to very severe, life-threatening
disease1. That the same GAS strain can cause infection
of various severity in different hosts indicates that host
genetic components seem to play an important role in
determining susceptibility to GAS infections2-4. The
investigation on the influence of host genetic factors on
susceptibility to Streptococcus pyogenes and the
identification of the corresponding genes will help to
clarify the molecular mechanisms involved in the
pathogenesis of this infection. However, due to the
genetic heterogeneity of human populations and the fact
that susceptibility to infection is usually a complex
multifactorial trait, animal models are needed to
understand the role of host genetic factors. In the present
study, the mouse model of S. pyogenes infection was
used as an experimental tool to identify specific host
features that affected resistance/susceptibility to this
pathogen.
Material & Methods
Mice: Inbred, pathogen-free, 7-wk old A/J, BALB/c,
DBA/2, C3H/HeN, and CBA/J mice were purchased
from Harlan-Winkelmann.
Bacteria: S. pyogenes strain A20 (M type 23) was
obtained from the German Culture Collection
(DSM2071). Stock cultures were maintained at 70ºC
and were cultured at 37ºC in Todd-Hewitt broth
supplemented with 1 per cent yeast extract for about
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INDIAN J MED RES (SUPPL) MAY 2004
142
6 h. Bacteria were collected in mid-log phase, washed
twice with sterile phosphate buffered saline (PBS),
diluted to the required inoculum, and the number of viable
bacteria was determined by counting colony-forming units
(cfu) after diluting and plating in blood agar plates
(GIBCO, USA) containing 5 per cent horse blood.
Infection protocol and organ preparation: Mice were
inoculated with S. pyogenes in 0.2 ml of PBS via a lateral
tail vein. Infected mice were euthanized by CO 2
asphyxiation, and bacteria were enumerated after 48 h
in the liver and spleen by preparing homogenates of these
organs in PBS and by plating 10-fold serial dilutions on
blood agar. Colonies were counted after 24 h of
incubation at 37ºC.
Results
Different inbred mouse strains differed markedly in
their survival time after infection with S. pyogenes:
After systemic infection with 105 cfu of S. pyogenes,
inbred mice showed substantial differences in mortality.
Results showed that while some mouse strains were very
resistant to GAS and survived infection (DBA/2 and
BALB/c), others (CBA, C3H/HeN and A/J) were highly
susceptible and their survival times after bacterial
inoculation did not exceed 4 days (Table).
Bacterial burden in spleen and liver of mice after
48 h of infection with S. pyogenes: Led to organ
colonization (Fig.) and tissue damage. Mice from
Table. Mean survival times of different mouse strains after
intravenous infection with S. pyogenes
Mouse strain
different strains were infected intravenously with
105 cfu of S. pyogenes. After 48 h, mice were scarified
by CO2 asphyxiation and the bacterial burden was
quantified in the livers and spleens. A significantly
higher number of bacteria was found in the organs of
CBA, C3H/HeN and A/J than in the organs of DBA/2
and BALB/c mice.
Discussion
Epidemiological evidences indicated that host genetic
factors might be critical on determining the outcome of
GAS infection4. This strongly suggests that the presence
or absence of specific host genes will determine how
effectively GAS infection will be resolved. However, the
molecular mechanisms and gene(s) involved in resistance/
susceptibility to GAS remain to be elucidated. The mouse
model provides an optimal experimental environment in
which the mechanisms responsible for susceptibility to
GAS infection can be characterized by simple comparison
of the course of infection and immunological parameters
in resistant and susceptible mice.
It is to be expected that the analysis of gene
interactions in the control of pathogenesis of
S. pyogenes infection can be powerful means for
understanding the interplay between host resistance and
S. pyogenes virulent factors. A clearer delineation of
these events in the mouse will increase our
understanding of streptococcal pathogenesis in humans
and help to the design of more effective therapeutical
approaches.
MST
(days)
CBA
2.3±0.4
C3H/HeN
3.3±0.3
A/J
2.2±0.4
BALB/c
*
DBA/2
**
Female mice were used in the experiment.
MST, mean survival time in days.
*100 per cent survival.
**90 per cent survival.
Fig. Bacterial loads in the systemic organs of genetically different
inbred strains of mice 48 h after infection with 105 cfu of S. pyogenes.
GOLDMANN et al: HOST GENETIC FACTORS IN GAS INFECTION
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Reprint requests: Dr Eva Medina, Division of Microbiology, Department of Microbial Pathogenesis & Vaccine Research,
GBF-National Research Centre for Biotechnology, Moscheroder Weg 1, 38124, Braunschweig, Germany
e-mail: [email protected]