Characterization of vibrio parahaemolyticus isolated in healthy carriers by using serotyping, biotyping and PCR for their virulence genes

Abstract

Many studies show that Vibrio parahaemolyticus can be detected from healthy contacts of diarrheal patients, villagers living near the sea, and healthy employees from seafood processed plants without showing any symptom of diarrhea. The carrier state of these healthy carriers who harbour V. parahaemolyticus has not been characterized. In this research, serotypes and virulence genes of V. parahaemolyticus were studied in 10,214 rectal swab samples from healthy workers of the frozen seafood plant and frozen processed seafood plant in a province, next to Bangkok. V. parahaemolyticus was found in 147 samples (1.4%) from 139 healthy workers throughout the year. Heiberg’s type VII (ferment sucrose, and mannose, but not arabinose) and type V (Ferment sucrose, and mannose, and arabinose) of V. parahaemolyticus were found in 64% and 18% of the samples, respectively. The isolates from another 18% of the samples tested positive for both Heiberg types. A total of 64 O.K. serotypes were identifiled among 999 isolates of V.parahaemolyticus from 147 positive samples, with 01:KUT (untypable) which was the most dominant serotype (11.9%), followed by 05:KUT (11.5%), 010:KUT (8.0%) and 011:KUT(7.1%). Only 1.7% of 999 isolates produced both thermostable direct hemolysin (TDH) and urease enzyme (TRH), whereas 32.8% of isolates produced only TDH and 8% produced only urease enzyme. Furthermore, 269 of 999 isolates were selected on the basis of their defferent heiberg types and serotypes form all positive samples to determine their virulence genes (tdh and trh) by using multiplex PCR and antimicrobial susceptibillty pattern. Both tdh and trh genes were positive in 4.8% of the isolates, 25.3% contained only tdh, 4.8% only trh and 65.1% were tdh trh. All isolates with trh produce urease enzyme and 7.4% of tdh isolates did not produce TDH. Antimicrobial susceptibility of the 269 isolates were tested with 8 antimicrobial agents, and more than 96% of them were susceptible to norfloxacin, nalidixic acid, nitrofurantoin, tetracycline, cotrimoxazole and gentamicin. Of the isolates, 27.9% and 17.8% were resistant to ampicillin and colistin, respectively. Multidrug resistant patterns were also found in 7.8% of 269 isolates, in which 5.9% showed resistance to ampicillin and colistin. Five transient healthy carriers from the frzen processed seafood plant were V. parahaemolyticus positive two to three times during the study period. However, all isolates from each transient healthy carrier were of different serotypes and strains. TDH with tdh isolate and TRH with trh isolate were identified in two carriers, This study has shown the significant findings and characteristics of V. parahaemolyticus among healthy carriers in the frozen seafood plants. Further research is suggested on the roles of carriers in transmission pathogenic mechanism and virulence gene expression