Serological and molecular characterization of Vibrio parahaemolyticus marine strains carrying pandemic genetic markers

In 2005, pandemic Vibrio parahaemolyticus was reported to have been introduced in Europe: O3:K6 strains were isolated from clinical cases in France and Spain, and were found to be associated with consumption of contaminated seafood. On the contrary, pandemic strains were not isolated from seafood or from the environment itself. Analysis of two V. parahaemolyticus strains isolated in May 2007 from Northern Italy seawater and plankton samples revealed the presence of the virulence gene tdh and the pandemic-specific markers orf8 and toxRS/new sequence (group-specific PCR). The two strains showed serotypes not included in the ‘pandemic group’, but their molecular typing proved that they represent a single clone showing a genetic profile very similar to that of pandemic O3:K6 reference isolates. Moreover, the two marine strains carried three virulence-related genes associated with clinical strains and, to date, hardly ever or never detected in environmental strains. The presence, in strains isolated from the marine environment, of genetic pandemic markers and virulence genes normally associated with clinical isolates proves that marine strains might constitute a public health concern.