Characterization of Vibrio parahaemolyticus strains isolated from marine fish and shell fish

Abstract

A total of forty two samples comprising of marine fish and shellfish samples comprising of farmed Litopenaeus vannamei, farmed Litopenaeus vannamei-cooked, farmed Penaeus monodon , and marine shrimp procured from Visakhapatnam, Andhra Pradesh were analysed for the presence of V. parahaemolyticus. Nine samples of marine fish and one sample of marine shrimp were positive for the presence of V. parahaemolyticus but all the farmed shrimp samples were negative. The V. parahaemolyticus isolates were confirmed using V. parahaemolyticus specific PCR targeting tl and flaE genes. All the V. parahaemolyticus isolates were negative for thermostable direct haemolysin (tdh) gene and none of them belonged to the highly virulent O3 colon K6 serogroup. The genetic heterogeneity of V. parahemolyticus isolates from marine fish was tested by employing ERIC- PCR. V parahaemolyticus isolates were clustered in to four distinct groups at 55 per cent similarity level. Group one comprised of the MTCC and ATCC type cultures and a field isolate of V. parahaemolyticus. However, majority of the V. parahaemolyticus isolates from marine fish were clustered in Group 2 at 80 per cent similarity level. The V. parahaemolyticus isolates VP4 and VP8 showed lesser similarity of 68 per cent and 55 per cent respectively and were delineated separately. Thyme oil at 0.25 per cent completely inhibited caseinase activity of V. parahaemolyticus whereas gelatinase activity was inhibited at 0.5 per cent level. Amylase and DNAse activities of the V. parahaemolyticu isolates decreased with increasing concentration of thyme oil but enzymatic activity was still observed at 1 per cent thyme oil level.