Campylobacter Epidemiology – Insights from Subtyping by Pulsed-Field Gel Electrophoresis

Höök, H. 2005. Campylobacter epidemiology – insights from subtyping by pulsed-field gel electrophoresis. Doctoral thesis. ISSN 1652-6880, ISBN 91-576-6988-0 Campylobacter jejuni and Campylobacter coli are frequent worldwide causes of food-borne gastroenteritis. Poultry is regarded as the most important infection source. In temperate countries, a marked seasonal variation of human campylobacteriosis is seen, with most cases occurring during the warmer season. In this PhD project, pulsed-field gel electrophoresis, PFGE, was used to explore the genetic and epidemiological relationships among both campylobacters colonising broilers and campylobacters causing sporadic infection in humans. In a commercial broiler flock, a subsequent addition of genotypes occurred during rearing, with two types found at two weeks of age and six types on the day before slaughter. Two new types were found in the slaughter samples. In two-thirds of the individual birds sampled the day before slaughter, more than one type were found. In two separate studies, Campylobacter isolates from humans infected in Sweden were characterised by PFGE. Although a large variation in distinct restriction patterns was found, most isolates could be sorted into clusters based on pattern similarities. Isolates in some clusters and subclusters were significantly more seasonally concentrated than other isolates. A sequenced strain of C. jejuni, NCTC 11168, was used as a reference strain and molecular size marker for PFGE. Using a Campylobacter strain for this purpose may be advantageous compared with using commercially available molecular markers, as the more sample-like DNA migration patterns facilitate and refine interpretation and analysis. In conclusion, PFGE was found to be a useful tool for investigating Campylobacter epidemiology in both broilers and humans. The results show that multiple genotypes of C. jejuni may be present in a commercial broiler flock during rearing and even in gastrointestinal tracts of individual birds. Both recurring environmental exposure and genetic changes within the population may explain the genotype diversity. Although a large number of genotypes may be found among Campylobacter strains infecting humans, a large proportion of these may be genetically related. It seems that certain Campylobacter genotypes infect humans in the regions studied during a short period of the year, and that these genotypes account for a substantial proportion of the cases during the season (summer and early autumn) with highest campylobacteriosis incidence.