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Fimbrial phase variation and systemic E. coli infection studied in the mouse peritonitis model
B Nowicki1, J Vuopio-Varkila, P Viljanen
1Department of General Microbiology, University of Helsinki, Finland.
Abstract:
Mouse peritonitis induced by intraperitoneal injection of a virulent (LD50 4 x 10(5) E. coli 018:K1:H7 strain isolated from neonatal meningitis was studied. These bacteria are capable of producing both type 1 and S fimbriae, binding to mannose or sialic acid containing glycoconjugates, respectively; the production of both fimbrial types is subject to phase variation. A broth culture of the bacteria was fractionated into subpopulations containing either type 1 or S fimbriae or neither (nonfimbriated cells), and each fraction, grown in broth to logarithmic growth phase, was used to infect groups of mice. The type 1 fraction was associated with decreased virulence as the fraction was eliminated rapidly without causing a progressive infection even at 10(6) bacteria/mouse, whereas both S and nonfimbriated cells started rapid multiplication in the peritoneal cavity and spread to the blood. In nonfibriated cells, however, S fimbriae production was induced at the same time so that at 1 h after injection, 60-70% of the bacteria in the peritoneal cavity and in the blood of the mice had S fimbriae. The injected S-fimbriated fraction remained completely S-fimbriated. Rapid induction of S fimbriae also took place in vitro when the nonfimbriated bacteria were grown in mouse serum or peritoneal fluid. Anti-S serum protected the mice from a lethal dose of S-fimbriated bacteria.
Insights
Type 1 fimbriae reduced E. coli virulence in mouse peritonitis models. S fimbriae and nonfimbriated cells multiplied rapidly, with S fimbriae induction observed in vivo and in vitro.
Area of Science:
- Microbiology
- Immunology
- Pathogenesis
Background:
- Escherichia coli strains causing neonatal meningitis possess type 1 and S fimbriae.
- Fimbrial expression is subject to phase variation, influencing bacterial adhesion and virulence.
- Understanding fimbrial roles is crucial for combating bacterial infections.
Purpose of the Study:
- To investigate the virulence of different Escherichia coli 018:K1:H7 subpopulations in a mouse peritonitis model.
- To determine the role of type 1 and S fimbriae in E. coli pathogenesis.
- To examine the induction and stability of S fimbriae during infection.
Main Methods:
- Induction of peritonitis in mice using virulent E. coli 018:K1:H7.
- Fractionation of bacterial cultures into type 1 fimbriated, S fimbriated, and nonfimbriated subpopulations.
- Infection of mice with each bacterial fraction and monitoring of bacterial growth and dissemination.
- In vitro induction of S fimbriae in mouse serum and peritoneal fluid.
Main Results:
- Type 1 fimbriated E. coli showed decreased virulence and rapid clearance.
- S fimbriated and nonfimbriated cells exhibited rapid multiplication and systemic spread.
- Nonfimbriated cells rapidly induced S fimbriae in vivo and in vitro, particularly in mouse serum.
- S fimbriated cells maintained their fimbriation status throughout the experiment.
- Anti-S serum provided protection against lethal doses of S-fimbriated bacteria.
Conclusions:
- Type 1 fimbriae are associated with reduced virulence in this model.
- S fimbriae play a significant role in E. coli virulence and dissemination.
- Environmental cues, like mouse serum, can rapidly induce S fimbriae expression.
- Targeting S fimbriae represents a potential therapeutic strategy against E. coli infections.