The impact of phase variation of Campylobacter jejuni genes on surviving host imune responses and for host adaptation

Abstract

Campylobacter jejuni is a spiral-shaped, flagellated Gram negative bacterium that requires a low oxygen level to grow. C. jejuni colonises the chicken caeca and infects humans mostly through consumption of contaminated chicken meat. C. jejuni is a major cause of severe gastroenteritis with bloody diarrhoea in humans worldwide. The genomic sequences of C. jejuni have several highly mutable polyG/polyC tracts containing seven or more G/C residues, which generate variation by either insertion or deletion of one or more of these repetitive residues. Mutations in the simple sequence repeat (SSR) tracts of C. jejuni switch the expression of the gene between ‘on’ and ‘off’. These strain-specific SSRs can mediate phase variation which is an additional way to adapt and modify bacterial fitness. The phenomenon of phase variation is reversible, stochastic, and leads to frequent switches in gene expression. This study focuses on two unpublished C. jejuni isolates LE104 and LE17, and aimed to investigate the project hypothesis that PV can empower C. jejuni to survive and adapt to the host’s immune responses, and that the function and the expression of the PV genes can influence bacterial survival. A PV assay was developed including; monoplex and multiplex PCR, fragment length analysis (Genescan) and PSAnalyse together with bioinformatics analyses. Outputs of these approaches confirmed gene presence and absence and compared the capsular and flagellar genes among different C. jejuni strains. Also, two different serum bactericidal assays were performed using different C. jejuni isolates. These results have allowed linkage of PV genes to conserved functions and possible behaviours in the host. And based on the results of these PV assays, some suggestions have been made for future work