Prevalence and Characterization of Typical and Atypical Escherichia coli from Fish Sold at Retail in Cochin, India

Abstract

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-β-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.