Molecular characterization of locus of enterocyte effacement pathogenicity island in shigatoxic Escherichia coli isolated from human & cattle in West Bengal, India

BACKGROUND & OBJECTIVES: Shigatoxic Escherichia coli (STEC) recovered from dairy animals of Kolkata, India, harboured the putative virulence genes; however, the animals did not exhibit clinical symptoms. Similarly, human isolates in this locality also showed variations in degree of symptoms. Hence, this study was designed to know the presence of recognized gene(s) in the locus of enterocyte effacement (LEE) pathogenicity island in these STEC isolates and functional status of the cardinal gene (eae) related to pathogenicity. METHODS: Genes were characterized using polymerase chain reaction (PCR) assays, and functional status of cardinal gene (eae) was evaluated by fluorescent actin staining (FAS) assay. Variation in eae gene was determined by intimin PCR. RESULTS: Cattle STEC isolates carried 22 genes in LEE pathogenicity island in different frequencies ranging from 5.63 to 47.88 per cent of the isolates. In human isolates, the genes namely ler, escRSTU, orf2, escC, escV, orf3 and tir that are associated with secretory function, were found to be absent and rest of the genes were present in lower frequency. Further, the cardinal gene (eae) responsible for initiation of pathogenesis was in a very low frequency in human (n=2; 10.5%) and cattle (n=11; 15.5%) isolates. None of these eae(+) STEC isolates from human and cattle revealed positivity in FAS assay. INTERPRETATION & CONCLUSIONS: Majority of human STEC isolates lacked the cardinal virulence gene (eae), and genes for secretory function that are essential for facilitating pathogenesis. This may partially be attributed to low occurrence of STEC in human clinical diarrhoea in this area. Although a few isolates (11 of 71) from cattle had eae gene, they did not express phenotypically. This could be one of the reasons for not appearing of clinical symptoms in the hosts.