Levels of Vibrio parahaemolyticus and thermostable direct hemolysin gene-positive organisms in retail seafood determined by the most probable number-polymerase chain reaction (MPN-PCR) method

Abstract

The incidence and levels of Vibrio parahaemolyticus and thermostable direct hemolysin gene (tdh)-positive organisms in retail seafood were determined. The most probable number-polymerase chain reaction (MPN-PCR) method using a PCR procedure targeting the species-specific thermolabile hemolysin gene (tlh) and tdh was used to determine the levels of V. parahaemolyticus and tdh-positive organisms, respectively. In seafood for raw consumption, V. parahaemolyticus was found in four (13.3%) of 30 fish samples, 11 (55.0%) of 20 crustacean samples, and 29 (96.7%) of 30 mollusc samples. Levels of V. parahaemolyticus were below 104 MPN/100 g in all fish and crustacean samples tested. However, they were above 104 MPN/100g in 11 (36.7%) of the 30 mollusc samples. In all seafood for raw consumption, the level of tdh-positive organisms was below the limit of detection (< 30 MPN/100 g). In seafood for cooking, V. parahaemolyticus was found in 15 (75.0%) of 20 fish samples, nine (45.0%) of 20 crustacean sample, and 20 (100%) of 20 mollusc samples. Levels of V. parahaemolyticus were above 104 MPN/100 g in only three (15.0%) and one (5.0%) of the 20 fish and 20 crustacean samples, respectively. However, they were above 104 MPN/100 g in 18 (90.0%) of the 20 mollusc samples. In seven (35.0%) of the 20 mollusc samples, tdh-positive organisms were found and their levels ranged from 3.6×10 to 1.1×103 MPN/100 g. From four of seven tdh-positive samples, tdh-positive V. parahaemolyticus was isolated.