Biodiversity of Clostridium botulinum type E strains isolated from fish and fishery products

The genetic biodiversity of Clostridium botulinum type E strains was studie d by pulsed-field gel electrophoresis (PFGE) with two macrorestriction enzy mes (SmaI-XSnaI and XhoI) and by randomly amplified polymorphic DNA (RAPD) analysis with two primers (OPJ 6 and OPJ 13) to characterize 67 Finnish iso lates from fresh fish and fishery products, 15 German isolates from farmed fish, and D isolates of North American or North Atlantic origin derived mai nly from different types of seafood. The effects of fish species, processin g, and geographical origin on the epidemiology of the isolates were evaluat ed. Cluster analysis based on macrorestriction profiles was performed to st udy the genetic relationships of the isolates. PFGE and RAPD analyses were combined and resulted in the identification of 62 different subtypes among the 92 type E isolates analyzed. High genetic biodiversity among the isolat es was observed regardless of their source. Finnish and North American or N orth Atlantic isolates did not form distinctly discernible clusters, in con trast with the genetically homogeneous group of German isolates. On the oth er hand, indistinguishable or closely related genetic profiles among epidem iologically unrelated samples were detected. It was concluded that the high genetic variation was probably a result of a lack of strong selection fact ors that would influence the evolution of type E. The wide genetic biodiver sity observed among type E isolates indicates the value of DNA-based typing methods as a tool in contamination studies in the food industry and in inv estigations of botulism outbreaks.