Genotypic diversity of Campylobacter lari isolated from mussels and oysters in The Netherlands

In order to gain insight into the epidemiology of Campylobacter lari infection in The Netherlands due to the consumption of raw mussels and oysters, batches of these shellfish were screened for the presence of Campylobacter spp. during a 6 month period in 1993-1994. Apparently, 41 out of 59 batches of mussels and 11 out of 41 batches of oysters were colonized with Campylobacter spp. A subset of the isolates was further characterized by additional phenotypic tests, numerical analysis of electrophoretic protein patterns, and genotyping by random amplification of polymorphic DNA (RAPD). Protein electrophoretic analysis of 39 Campylobacter spp. cultured from 24 batches of mussels and oysters, revealed that all isolates, except two, were C. lari. Two strains with an aberrant protein pattern were identified as C. coli and C. hyointestinalis, respectively. Nalidixic acid susceptible campylobacters (NASC) and urease-positive thermophylic campylobacters (UPTC) did not form separate clusters and should be considered biovars only. Several strains were both urease positive and nalidixic acid susceptible, which represents a new biovar within C. lari. The results of RAPD demonstrated the presence of 3 distinct genetic variants, implying that even within a single batch of shell fish, relatively extensive DNA polymorphisms can be found. It is therefore apparent that this complex group of C. lari is characterized by a high degree of genetic diversity, implying the presence of a heterogenous population of C. lari in crustacean organisms living in marine waters in a restricted area in The Netherlands.