Host-associated variability of the cdtABC operon, coding for the cytolethal distending toxin, in Campylobacter jejuni

Campylobacter, a major cause of food-borne gastroenteritis worldwide, colonize the gastrointestinal tract of a wide range of animals, being birds the main reservoir. The mechanisms involved in the interaction of Campylobacter with the different hosts are poorly understood. The cytolethal distending toxin, encoded in the cdtABC operon, is considered a pivotal virulence factor during human infection. Differences in the prevalence of cdtABC genes in Campylobacter isolates from three distinct origins (wild birds, broiler chickens and humans) prompted us to further characterize their allelic variability. The sequence of cdtABC is highly conserved among broiler and human isolates. A high diversity of cdtABC alleles was found among wild bird isolates, including several alleles that do not produce any functional CDT. These results suggest that specific variants of the cdtABC operon might define the host range of specific Campylobacter jejuni isolates. Moreover, our data indicate that PCR methodology is inaccurate to characterize the prevalence of the cdt genes, since negative PCR detection can be the result of divergences in the sequence used for primer design rather than indicating the absence of a specific gene.