Involvement of a plasmid in virulence of Campylobacter jejuni 81-176

Campylobacter jejuni strain 81-176 contains two, previously undescribed pla smids, each of which is approximately 35 kb in size. Although one of the pl asmids, termed pTet, carries a tetO gene, conjugative transfer of tetracycl ine resistance to another strain of C.jejuni could not be demonstrated. Par tial sequence analysis of the second plasmid, pVir, revealed the presence o f four open reading frames which encode proteins with significant sequence similarity to Helicobacter pylori proteins, including one encoded by the ca g pathogenicity island. All four of these plasmid-encoded proteins show som e level of homology to components of type IV secretion systems. Mutation of one of these plasmid genes, comB3, reduced both adherence to and invasion of INT407 cells to approximately one-third that seen with wild-type strain 81-176. Mutation of comB3 also reduced the natural transformation frequency . A mutation in a second plasmid gene, a virB11 homolog, resulted in a 6-fo ld reduction in adherence and an 11-fold reduction in invasion compared to the wild type. The isogenic virB11 mutant of strain 81-176 also demonstrate d significantly reduced virulence in the ferret diarrheal disease model. Th e virB11 homolog was detected on plasmids in 6 out of 58 fresh clinical iso lates of C. jejuni, suggesting that plasmids are involved in the virulence of a subset of C. jejuni pathogens.