Major tdh(+)Vibrio parahaemolyticus serotype changes temporally in the Bay of Bengal estuary of Bangladesh.

ABSTRACT

Vibrio parahaemolyticus is responsible for seafood-related gastroenteritis worldwide. In Bangladesh, diarrhea is endemic and diarrheagenic V. parahaemolyticus serotypes occur naturally in the coastal and estuarine aquatic environment. V. parahaemolyticus strains, isolated from estuarine surface water of the Bay of Bengal villages of Bangladesh during 2006-2008, were tested for the presence of virulence and pandemic-marker genes, serodiversity, and phylogenetic relatedness. PCR analysis of V. parahaemolyticus (n=175) showed 53 (30.3%) strains to possess tdh, the major virulence gene encoding thermostable direct hemolysin. Serotyping results revealed the tdh(+)V. parahaemolyticus strains to belong to 10 different serotypes, of which the O8K21 (30.2%) and O3K6 (24.5%) were predominantly non-pandemic and pandemic serotypes, respectively; while O5K30 and O9KUT were new. The pandemic markers, orf8 and toxRS(variant), were present only in the pandemic serotype O3K6 (n=13) and its serovariant O4K68 (n=2). Temporal distribution of the tdh(+) serotypes revealed the O8K21 to be predominant in 2006 and 2007, while O3K6 was the predominant tdh(+) serotype in 2008. Pulsed-field gel electrophoresis (PFGE) of SfiI-digested genomic DNA revealed high genetic diversity among the V. parahaemolyticus strains, while dendrogram constructed with the PFGE patterns formed two major clusters separating the tdh(+) O3K6 and its pandemic serovariants from the tdh(+) non-pandemic (O8K21) strains, suggesting different lineages for them. The potential health risk related to the prevalent tdh(+) strains, including the observed temporal change of the predominant tdh(+) serotype, from O8K21 to the pandemic serotype O3K6 in estuarine surface waters serving as the major source of drinking water suggests the need for routine environmental monitoring to prevent V. parahaemolyticus infection in Bangladesh.