EFFECT OF TEMPERATURE ON THE GROWTH OF ARTIFICIALLY SPIKED THREE DIFFERENT STRAINS OF Vibrio parahaemolyticus IN CLAMS
The present study was carried out to analyse the effect of altered temperature conditions on the growth of three different strains of V. parahaemolyticus viz., VP5, VP22 and VP12. Known doses of three strains of parahaemolyticus was injected into clams and kept at the following temperatures viz., 370C and 300C, 200C and 100C until the shells gaped. All the three strains of V. parahaemolyticus was multiplied rapidly in live clams held at 37°C and 300C (increase of 4 logs CFU/g at 20 and 25 h). V. parahaemolyticus in clams stored at 10°C and 20°C showed 2 log CFU/g and 1 log CFU/g decrease at 72 h and 136 h, respectively.
Vibrio parahaemolyticus is an important seafood borne human pathogen worldwide and associated with gastroenteritis outbreaks including India. Growth of pathogenic V. parahaemolyticus is influenced and altered by many environmental factors including temperature. The present study was undertaken to determine if there were any differences in growth of potentially pathogenic V. parahaemolyticus VP5 (tdh+trh-), VP22 (trh+tdh-) and VP12 (tdh+trh+) in relation to presence of virulence genes in clams (Meretrix meretrix) when exposed to different postharvest temperatures. Each set of depurated clams (Meretrix meretrix) were then spiked with known doses of pathogenic V. parahaemolyticus and kept at selected storage temperature. Similarly, the experiment was conducted for all the three strains. At selected time intervals, 3 - 5 of clams were homogenised and analysed for the growth of V. parahaemolyticus using MPN-PCR targeting tlh gene. It was observed that the growth variability among all the three strains was significant at all storage temperatures. In this study, VP5 (tdh+trh-) exhibited a rapid growth rate at 370C and 300C followed by 200C when compared with VP22 (trh+tdh-) and VP12 (tdh+trh+).
It was found that the growth was rapid at optimum and higher temperatures while the growth of V. parahaemolyticus was drastically reduced at 100C. This study revealed that the genotypes or strain variability also influences the growth pattern of V. parahaemolyticus. Largest growth variability was observed at stress/non optimal conditions. However, these results indicated that temperature near 100C represented the growth/no growth boundary for all the strains of V. parahaemolyticus and viability at this temperature was depended on strains. These results also showed that the storage of clams at 100C have a negligible impact on the risk of V. parahaemolyticus illness.
