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Escherichia coli is a common contaminant of seafood in the tropics and is often encountered in high numbers. The count of E. coli as well as verotoxigenic E. coli O157:H7 was estimated in 414 finfish samples composed of 23 species of fresh fish from retail markets and frozen fish from cold storage outlets in and around Cochin, India. A total of 484 presumptive E. coli were isolated, and their indole-methyl red-Voges-Proskauer-citrate (IMViC) pattern was determined. These strains were also tested for labile toxin production by a reverse passive latex agglutination method and checked for E. coli serotype O157 by latex agglutination with O157-specific antisera. Certain biochemical marker tests, such as methylumbelliferyl-beta-glucuronide (MUG), sorbitol fermentation, decarboxylase reactions, and hemolysis, which are useful for screening pathogenic E. coli, were also carried out. Results showed that 81.4% of the E. coli isolates were sorbitol positive. Among this group, 82% were MUG positive, and 14.46% of the total E. coli isolates showed human blood hemolysis. None of the isolates were positive for agglutination with E. coli O157 antisera nor did any produce heat-labile enterotoxin. This study indicates that typical E. coli O157 or labile toxin-producing E. coli is absent in the fish and fishery environments of Cochin (India). However, the presence of MUG and sorbitol-negative strains that are also hemolytic indicates the existence of aberrant strains, which require further investigation.

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Foodborne outbreaks attributed to the contamination of foods with enterohemorrhagic Escherichia coli (EHEC) O157:H7 are a growing global concern. Fish and shrimp samples obtained from different retail fish markets in Cochin, India, were screened by direct PCR assays targeting three important virulence markers of EHEC, the intimin protein (eaeA gene), enterohemolysin (hlyA gene), and Shiga toxin (stx gene). One shrimp (Fenneropenaeus indicus) sample was positive for all these virulence markers, and seven typical E. coli O157:H7 isolates were recovered from the marker-positive shrimp sample. This is the first report of recovery of typical E. coli O157:H7 from fish or shellfish in India. All the typical EHEC isolates had a characteristic reaction in eosin methylene blue agar and belonged to IMViC (indole, methyl red, Voges Proskauer, Simmons citrate reactions) biotype I. These isolates also were negative for sorbitol and methylumbelliferyl-beta-glucuronide and exhibited beta-hemolytic activity. One isolate showed self-agglutination for E. coli O157 antisera and produced a false-positive reaction with CHROMagar O157. These typical EHEC isolates belonged to a restricted biotype group and had a very low multiple antibiotic resistance index. Isolation of E. coli O157:H7 in fish and shellfish indicates that strict adherence to hygienic handling methods and proper cooking or processing is needed before consumption of these products.

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