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An environmentally regulated pilus-like appendage involved in Campylobacter pathogenesis
1Department of Biochemistry and Microbiology, University of Victoria, British Columbia, Canada.
Abstract:
Examination of strains of Campylobacter jejuni, Campylobacter coli, and Campylobacter fetus by electron microscopy revealed that they produced peritrichous pilus-like appendages when the bacteria were grown in the presence of bile salts. Various bile-salt supplements were used and it was found that deoxycholate and chenodeoxycholic acid caused a significant enhancement of pilus production and resulted in a highly aggregative phenotype. Morphologically, the pili were between 4 and 7 nm in width and were greater than 1 micron in length. A gene, termed pspA, which encodes a predicted protein resembling protease IV of Escherichia coli, was identified in C. jejuni strain 81-176. A site-specific insertional mutation within this gene resulted in the loss of pilus synthesis as determined by electron microscopy. Insertions upstream and downstream of the gene had no effect on pilus production. The non-piliated mutant of strain 81-176 showed no reduction in adherence to or invasion of INT 407 cells in vitro. However, this mutant, while still possessing the ability to colonize ferrets, caused significantly reduced disease symptoms in this animal model.
Insights
Bile salts induce pilus production in Campylobacter bacteria, with deoxycholate and chenodeoxycholic acid being particularly effective. A specific gene, pspA, is crucial for this pilus synthesis, impacting disease severity but not colonization.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Molecular Biology
Background:
- Campylobacter species are significant human pathogens.
- Pilus-like appendages in bacteria can play roles in adhesion and colonization.
- The role of bile salts in Campylobacter pilus production is not well understood.
Purpose of the Study:
- To investigate the effect of bile salts on pilus production in Campylobacter species.
- To identify the genetic basis for bile-induced pilus formation.
- To assess the role of pili in Campylobacter adherence, invasion, and disease.
Main Methods:
- Electron microscopy was used to visualize pili.
- Bile salt supplements were added to bacterial growth media.
- Genetic analysis, including site-specific insertional mutagenesis of the pspA gene, was performed.
- In vitro adherence and invasion assays using INT 407 cells were conducted.
- A ferret model was used to evaluate colonization and disease symptoms.
Main Results:
- Bile salts, especially deoxycholate and chenodeoxycholic acid, significantly enhanced pilus production and bacterial aggregation.
- Pili were morphologically characterized as 4-7 nm wide and >1 micron long.
- A gene, pspA, was identified and shown to be essential for pilus synthesis.
- A non-piliated mutant (pspA mutant) did not show reduced adherence or invasion in vitro.
- The pspA mutant exhibited reduced disease symptoms in ferrets but retained colonization ability.
Conclusions:
- Bile salts are potent inducers of pilus-like appendages in Campylobacter species.
- The pspA gene is critical for bile-induced pilus production.
- While pili are not essential for in vitro adherence or invasion, they contribute to the virulence and disease-causing potential of Campylobacter in vivo.