Campylobacter jejuni is a prominent food-borne pathogen and causative agent of Campylobacteriosis infection. This infection arises primarily from the consumption of foodstuffs/beverages previously contaminated with this microorganism. Despite current food control measures currently employed, this pathogen remains problematic despite its fastidious nature. To help control the spread of Campylobacter many hurdles are used in the food industry, including natural products such as modified atmosphere and salt. Other natural antimicrobials are shown to possess antibacterial activity. Chitosan, a natural antimicrobial, has promising uses in food production. However, little is known about the transcriptional differences of C. jejuni upon chitosan exposure. Molecular responses may allow for generation of adaptive responses in an attempt to combat such a stressor, possibly altering phenotypic and virulence potential. The aims of this study were to establish the adaptive response of C. jejuni to low molecular weight chitosan by assessing the phenotypic and molecular differences arising from the chitosan challenge. By exposing C. jejuni NTCT11168 to suboptimal levels of chitosan, based on MIC determination on a model system, an adaptive strain of C. jejuni has been developed. This newly developed isolate, referred to as the ‘adapted’ C. jejuni NCTC11168 was found to have enhanced antimicrobial tolerance to chitosan, with a 3.83 fold increase in MIC relative to the parental wild-type C. jejuni NCTC11168 cells (0.012% - 0.046% (w/v) respectively). Antimicrobial activity of chitosan was found to be pH dependant. Differences in motility were also apparent between the ‘adapted’ and wild-type strains. Consistent increases in motility were noted in the ‘adapted’ cells, especially in relation to wild-type after 24, 48 and 72 hours (p < 0.05). Biofilm formation was also enhanced especially in the ‘adapted’ isolate relative to the wild-type NCTC11168 cells. This was indicated by significant increases, most notably after 3 days formation (p < 0.05). Microarray analysis revealed significant alterations in transcriptional levels in response to chitosan exposure. Protein-encoding genes, believed to be associated with energy metabolism, solute/ion uptake/acquisition and efflux systems, were found to be differentially regulated when grown in the presence of low molecular weight chitosan (p < 0.05). Overlapping between initial comparisons revealed several genes, which were differentially regulated. Most notably, PEB3 (major antigenic peptide), Cj0017c (disulphide bond formation) and Cj0294 (thiamine biosynthesis) genes were found to be up regulated in ‘adapted’ C. jejuni cells when compared to the wild-type (p < 0.05). Whilst significant down regulation was found in the protein-coding genes, Cj0025c (putative sodium:dicarboxylate symporter) and Cj1608 (two-component regulator). These results indicate that regulation of these genes may contribute to enhanced phenotypic responses observed in the ‘adapted’ isolate of C. jejuni NCTC11168. These findings are likely to account for increased growth and survival of ‘adapted’ C. jejuni NCTC11168 when challenged to this antimicrobial, when compared to the wild-type. The findings in this study provide useful information as to how C. jejuni NCTC11168 can develop an adaptive tolerance response to chitosan and that alterations in transcriptional aspects may facilitate this, contributing to an enhanced phenotypic response and virulence potential.

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