Incidence and virulence properties of E. coli isolated from fresh fish and ready-to-eat fish products

Aim: To investigate the incidence and virulence properties of E. coli in fresh fish and ready-to-eat fish products from retail markets of the Ludhiana the present study was conducted. Materials and Methods: Total of 184 samples comprising 96 raw fish and 88 readyto-eat (RTE) fish products were collected from Ludhiana and other parts of Punjab and were subjected to suitable microbiological methods for E. coli isolation. E. coli isolates were subjected for haemolytic activity and indicators of plausible cytotoxicity (lecithinase, protease and gelatinase production), congo red dye biding assay. To assess virulence potential isolates were molecularly screened for stx 1 and 2 genes. Results: From raw fish samples 47(48.95%), E. coli, were isolated. From RTE fish products 7(12.96%), E. coli were isolated. Overall incidence for E. coli was 54 (29.34%). In vitro virulence characterization of isolates exhibited that all E. coli isolates were haemolytic while indicators of plausible cytotoxicity ( lecithinase, protease and gelatinase production) were in the range of 16.67% to 35.19% indicated that though the isolates were haemolytic they were perhaps less likely to be cytotoxic. Congo Red binding assay for E. coli isolates revealed that majority (88.89%) of the isolates failed to uptake the dye and only few (11.11%) could bind the dye. Results of serotyping revealed a total of 15 different serotypes among the E. coli isolates. More variation was observed among isolates from raw fish samples (12 serotypes) while RTE fish products harboured only 5 different serotypes. Molecular characterization of E. coli isolates revealed that PCR screening of isolates revealed that total 39 (72.22%) samples out of 54 E. coli isolates were positive for stx1 gene and 28 (51.85%) of isolates were positive for stx2 gene. Sources wise, 36 (66.66%) of isolates from raw fish and 3(5.55%) of isolates from RTE fish products were positive for stx1 while and stx2 gene could be detected in 24(44.44%) isolates from raw fish and 4(7.4%) isolates from RTE fish products.Interestingly, about 20% (37.03%) isolates were positive for both stx1 and stx2 genes. Among these multivirulent isolates majority (n=18) belonged to raw fish samples compared to a few (n=2) from RTE fish products. Conclusion: The results of the present study highlighted the possible risks to consumers of fish and fish products in the region that demand action to address this public health concern.