Investigation of the Influence of Phase Variation on the Biological Phenotypes and Immunity to the Flagella in Campylobacter jejuni

Campylobacter jejuni is the leading cause of foodborne bacterial gastroenteritis worldwide. Chickens are considered the main source of human infection. Flagellar-mediated motility plays a central role in commensal and pathogenic behaviours of C. jejuni. The FlaA protein, a major subunit of the flagellar filament, is decorated with variable glycans that are synthesised or attached by glycosylation enzymes. Some of these glycosylation enzymes are encoded by phase-variable genes that may have an influence on motility. The decoration of the flagella with sugar moieties is also likely to influence immune recognition. In this study, phase variation (PV) and whole genome sequence analyses of multiple motile and hypermotile variants of the C. jejuni 11168Ca strain showed that the formation of hyper-motility is associated with mutations in functional domains of the cbrR gene rather than the reversible expression of PV genes. This study also revealed the slow elicitation of C. jejuni-specific antibody responses following challenge of chickens against glycosylated FlaA (gFlaA) in contrast to fast responses to recombinant non-glycosylated FlaA (rFlaA) in birds after two weeks of colonisation. However, after 6 weeks of colonisation, all birds generated FlaA-specific antibodies against both gFlaA and rFlaA protein as detected in western blots. Similar reactivity for the flagella proteins in a range of flagellin glycosyltransferase mutants (non-PV gene; maf2 and PV genes Cj1295 and Cj1310c) was also observed. Finally, this study showed little to no influence of PV genes on motility and aggregation and strong association with colonisation via being expressed in a high proportion of colonies. In conclusion, this study showed a potential role for glycosylated PV genes in delaying C. jejuni-specific FlaA antibody responses as a mechanism for long-term colonization in chickens.