High Prevalence of Antibiotic Resistance and Integrons in Escherichia coli Isolated from Urban River Water, India.

The contamination of surface waters with multidrug resistant (MDR) coliforms is a major public health concern in developing countries. This study was aimed to evaluate the occurrence of antibiotic resistance and role of integrons in the spread of resistance genes in Escherichia coli isolated from urban waters of river Yamuna. One hundred and forty-one strains of E. coli were isolated and assessed for antibiotic resistance wherein high resistance was observed for Cefazolin. Integrons (class 1 and class 2) were detected in 32% of the isolates. Variable region of class 1 integron carried different gene cassettes, namely. dfrA17-aadA5, dfrA12-orfF-aadA2, bla-aadA1, and unusual phage tail tape measure protein. These integron-positive isolates were further characterized by phylogrouping, serotyping, and BOX-PCR typing. Phylogroup B2 was found to be the most prevalent. Pathogenic E. coli O157 was also reported. Majority of the isolates (54%; 7/13) carrying "dfrA17-aadA5" gene cassette were clustered predominantly into a single BOX-PCR type (B), suggesting a genetic relatedness among the isolates. This study thus depicts very high incidence of multidrug resistance and class 1 integrons in surface water of India. The prevalence of integrons in aquatic E. coli correlated well with resistance to increasing number of antibiotic classes and multiple antibiotic resistance (MAR) index at various sites. Integron-positive MDR E. coli isolates were found to be serologically and genetically diverse suggesting major role of integrons in the emergence and dissemination of resistance traits in waterborne E. coli.