Persistence of sucrose fermenting and nonfermenting vibrios in tissues of Manila clam species, Ruditapes philippinarum, depurated in seawater at two different temperatures

Effective post-harvest treatment to eliminate toxigenic vibrios is an important measure to reduce risk associated with seafood consumption. In the present study, we examined whether natural populations of sucrose nonfermenting (SNFV) and sucrose fermenting vibrios (SFV) persisted in Ruditapes philippinarum, after depuration at two different temperatures. Two experiments (one in Spring and one in Summer) were performed. Clams were depurated in duplicate tanks in an open-circuit seawater system using filtration and ultraviolet treatment. Clams were sampled daily (9 days), individually processed and inoculated on thiosulphate-citrate-bile salts-sucrose (TCBS) agar plates to estimate the density of SNFV and SFV. Results showed that depuration was less effective in Summer than in Spring, for SNFV and SFV. Despite an initial lower presence in the Summer experiment, clearance of SNFV was less efficient than in Spring, with 22.2% of clams presenting SNFV on day 8 and without significant changes on day 9. When compared, daily proportion of presence of SNFV and SFV in Spring, it was observed that SFV were more frequent than SNFV on days 8 and 9. In Summer these differences were significant on days 7-9. Present study demonstrated that SNFV (involved in food poisoning) are purged, at any temperature, faster than SFV.