Survival of Animal-derived Campylobacter Strains in Raw and Pasteurized Milk, and the Roles of Capsule in Campylobacter Survival in vitro, and in Chick Colonization

Abstract

Campylobacter spp. is a major cause of acute bacterial gastroenteritis in the developed countries. It can survive in a wide range of environments, raw milk and poultry are major reservoirs. Survival of animal-derived Campylobacter strains, including six C. jejuni and six C. coli, was examined in raw and pasteurized milk at 4oC. Most (11/12) of the Campylobacter strains survived in both raw and pasteurized milk for at least 14 days. The most resistant strain, a C. jejuni from a dairy cow, retained its viability over eight weeks in pasteurized milk, while the most sensitive strain showed a > 5-log10 CFU/ml reduction in raw milk after one week. The majority (9/12) of the strains survived better in pasteurized milk than in raw milk, while the opposite was observed for two C. coli strains. The findings indicate that Campylobacter spp. can survive in milk for at least 14 days at 4oC and that survival is strain-dependent. To elucidate mechanisms underlying such adaptation, we characterized the role of capsule in Campylobacter survival in milk and other media, and in chick colonization. Three capsule-deficient mutants (kpsM::kanr), C. coli 6979M2, C. jejuni BS142M2 and C. jejuni SC1453M2 were constructed by site-specific mutagenesis. Compared to the wild type strains, the colonies of the mutants were smaller, more convex, and shinier on agar media; the mutants were more sensitive to desiccation and two (C. coli 6979M2 and C. jejuni BS142M2) grew slower in broth. These two mutants were also more sensitive to certain antibiotics than their wild type counterparts. The survival of the mutants in distilled water, raw and pasteurized milk was comparable to survival of their wild type counterparts, as was the ability of the bacteria to transform to nalidixic acid resistance via transformation. In chick colonization experiment, C. coli 6979 M2 showed > 3log10 reduced cell density in cecal contents than its parent strain. These results suggest that capsule is essential for C. coli in chick colonization and responsible for colony morphology on solid agar and can protect cells from desiccation, but its impact on growth rate, competence and antibiotic resistance is strain-dependent.