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Change in degree of type 1 piliation of Escherichia coli during experimental peritonitis in the mouse
Abstract:
To determine whether expression of type 1 pili varies during the course of Escherichia coli infection in vivo, mice were injected intraperitoneally with 5 X 10(7) CFU of piliated or nonpiliated phase variants per ml, and the degree of piliation was measured in peritoneal exudate by an enzyme-linked immunosorbent assay inhibition method. In the animals challenged with the piliated bacteria, the numbers of organisms increased a log over 9 h and the amount of pilus antigen decreased from 3 to 0.075 micrograms/10 bacteria. After a 4-h delay, nonpiliated bacteria also increased by one log over 9 h; however, the amount of piliation remained virtually undetectable. Piliated E. coli were more virulent than nonpiliated variants in this model (50% lethal dose of 7.5 X 10(6) versus 3 X 10(7), respectively). The difference was significantly reduced by prior passive immunization with rabbit serum containing high titers of antipili antibody. Piliated bacteria adhered in significantly greater numbers to isolated mouse peritoneal membranes than did nonpiliated variants (15,400 +/- 2,700 versus 1,300 +/- 700 bacteria/mm2, respectively; P = 0.05). Adherence was inhibited by the presence of 0.1 M alpha methyl mannose (1,500 +/- 1,800 bacteria/mm2, P = 0.01). These results confirm the results of previous qualitative studies showing that phase variation of type 1 pili occurs in vivo and suggest that these pili may confer an initial advantage for growth of E. coli in the peritoneal cavity, presumably by fostering colonization of the peritoneal serosal surface.
Insights
Type 1 pili expression in Escherichia coli varies during infection. Piliated E. coli show increased virulence and peritoneal colonization, suggesting pili aid initial bacterial growth.
Area of Science:
- Microbiology
- Infectious Diseases
- Bacterial Pathogenesis
Background:
- Escherichia coli (E. coli) possesses type 1 pili, which are surface appendages involved in bacterial adhesion and virulence.
- Phase variation allows E. coli to switch between piliated and nonpiliated states, potentially influencing host-pathogen interactions.
- Understanding the in vivo behavior of E. coli phase variants is crucial for elucidating infection dynamics.
Purpose of the Study:
- To investigate the in vivo expression and role of type 1 pili during experimental Escherichia coli infection in mice.
- To determine if type 1 pili influence E. coli virulence, growth, and adherence in the peritoneal cavity.
- To assess the impact of phase variation on E. coli's ability to colonize host tissues.
Main Methods:
- Mice were intraperitoneally injected with piliated or nonpiliated E. coli phase variants.
- Piliation levels were quantified using an enzyme-linked immunosorbent assay (ELISA) inhibition method.
- Bacterial growth, virulence (assessed by 50% lethal dose), and adherence to peritoneal membranes were measured.
- The effect of antipili antibodies and alpha-methyl mannose on bacterial adherence was evaluated.
Main Results:
- Type 1 pili expression decreased significantly as piliated E. coli replicated in the mouse peritoneal cavity.
- Piliated E. coli exhibited greater virulence and adherence to peritoneal membranes compared to nonpiliated variants.
- Bacterial adherence was mediated by mannose-sensitive interactions, characteristic of type 1 pili.
- Passive immunization with antipili antibodies reduced the virulence difference between piliated and nonpiliated strains.
Conclusions:
- Type 1 pili expression undergoes phase variation in vivo during E. coli peritonitis.
- Type 1 pili likely confer an initial advantage for E. coli colonization and growth in the peritoneal cavity.
- Pili-mediated adherence to the peritoneal serosal surface appears to be a key factor in early infection stages.