The thermotolerant coliforms (201) isolated from various sources of drinking water were studied for antibiotic sensitivity and tolerance to heavy metals. Predominant resistance to bacitracin, vancomycin, and ampicillin was detected among thermotolerant coliform species. Forty one percent strains of thermotolerant coliforms were found to be multiple antibiotics resistant (MAR). All strains of Escherichia coli were found resistant to bacitracin. Resistance to commonly used antibiotics such as ampicillin, streptomycin, tetracycline and chloramphenicol was observed in <10% E. coli studied. Majority (85.0%) of Klebsiella were resistant to bacitracin and vancomycin. Resistance to ampicillin was found in 54.8% Klebsiella studied. Sixty seven percent Klebsiella were MAR. Majority (80.0%) of E. coli were found to be resistant to arsenic, chromium, copper and cadmium. Tolerance to zinc, nickel and mercury was observed among 70.0% isolates. In the case of Klebsiella species, prevalent tolerance to chromium, arsenic, cadmium, mercury and copper was observed. Twenty-four (24) strains of thermotolerant coliforms were studied for their ability to transfer their resistance(s). All strains had the ability to transfer one or more resistance traits. Thirty-three (33) thermotolerant coliforms cultures were tested for the curing of R-plasmid using acridine orange as a curing agent. In the case of antibiotics, curing was observed for streptomycin, cephaloridine and kanamycin. In the case of heavy metals, curing of plasmid for nickel, copper, cobalt, mercury and chromium was observed in >70.0% strains. Low level (27.2%) of curing to arsenic was detected. Among heavy metals, curing by nickel, chromium, zinc, cobalt and copper was detected in >78.0% E. coli strains. In almost half strains of Klebsiella spp., resistance to kanamycin was cured. Nine strains of thermo-tolerant E. coli representing different resistance pattern showed the presence of plasmid DNA. In this study, the occurrence of antibiotic resistance among thermotolerant coliform isolates from rural drinking water in India was investigated. At the same time, the R-plasmid transfer frequencies of the antibiotic resistance among thermotolerant coliforms were also evaluated.
Keywords: Antibiotic resistance, heavy metal, pathogenic, Escherichia coli, bacitracin, plasmid.