Characterization of pathogenic Vibrio parahaemolyticus isolates from clinical sources in Spain and comparison with Asian and North American pandemic isolates

In spite of the potential risk involved with contamination of seafood with Vibrio parahaemolyticus, there is a lack of information on the occurrence of pathogenic V. parahaemolyticus in Europe. This organism was isolated in 1999 from a large outbreak (64 cases admitted to a single hospital) associated with raw oyster consumption in Galicia, Spain, one of the most important regions in shellfish production worldwide. Two V. parahaemolyticus isolates from the 1999 Galicia outbreak, three additional clinical isolates obtained in the same period from hospitals in Spain, two reference strains from clinical sources, and five Spanish environmental isolates were examined. Seventeen isolates belonging to the pandemic clone isolated in Asia and North America were included in the study for comparison. All isolates were characterized by serotyping, PCR for virulence-related genes, pulsed-field gel electrophoresis (PFGE), and plasmid analysis. Four of the five clinical isolates from hospitals in Spain belonged to serotype O4:K11; the remaining isolate was O4:K untypeable (KUT). All five isolates were positive for V. parahaemolyticus toxR and tlh (species-specific genes) and tdh and negative for trh and group-specific PCR (a PCR method for detection of the pandemic clone). PFGE analysis with NotI and Still discriminated the European isolates in two closely related PFGE types included in a homogeneous cluster, clearly differentiated from the Asian and North American isolates. The five environmental isolates belonged to serotypes O2:K28, O2:KUT, O3:K53, O4:KUT, and O8:K22 and were negative for all virulence genes. The five isolates were discriminated into five different PFGE types unrelated to any other isolate included in the study. While the virulence characteristics (tdh positive, trh negative) of the Spanish clinical isolates matched those of the O3:K6 clone from Asia and North America, they were clearly excluded from this clone by group-specific PCR, PFGE, and serotyping. The results of this study suggest that a unique and specific clone could be related to the V. parahaemolyticus infections in Europe.