Virulence gene expression, adhesion and invasion of Campylobacter jejuni exposed to oxidative stress (H2O2).

Studies were undertaken to investigate the effect of oxidative stress conditions (exposure to hydrogen peroxide, H2O2) on [1] the expression of 14 Campylobacter jejuni virulence-associated genes associated with motility and/or invasion (flaA, flaB, flhA, flhB, ciaB, iamA), adhesion (cadF), cytotoxin production (cdtA, cdtB, cdtC) as well as some of the regulators of these genes (rpoN, fliA, luxS, cj1000), in 10 C. jejuni strains (5 poultry and 5 human) and [2] the ability of these cells to adhere to and invade Caco-2 cells. Using 16S rRNA as the reference gene (preliminary research demonstrated that this gene was stably expressed), the expression of the 14 virulence associated genes was investigated under normal and oxidative stress conditions using reverse transcription PCR. A Caco-2 cell tissue culture assay was used to examine adhesion and invasion. The response to oxidative stress was strain-dependent. Two strains showed significant (p<0.05) up or down regulation in 7 of the 14 genes tested, while only 1-2 genes were affected in the remaining strains. Expression of cadF was significantly (p<0.05) changed in all strains, cdt B in 4 strains and cj1000 in 3 strains. Expression of the remaining genes was either unaffected or significantly altered in 1-2 strains. NCTC 11168 completely lost the ability to adhere to and invade Caco-2 cells. One other strain also demonstrated reduced adherence while two others were unable to invade Caco-2 cells after exposure to oxidative stress conditions. In contrast strain 7, a poultry isolate, showed increased invasion. It was concluded that oxidative stress affects expression of C. jejuni virulence genes in a strain-dependent manner, CadF may have a secondary survival function and the cdtB gene may have a different promoter than cdtA and cdtC.