Occurrence of chromium resistant thermotolerant coliforms in tannery effluent

Twenty six thermotolerant strains resistant to high levels of chromium (50-250 microg/ml) were isolated from treated tannery effluent. They were also found resistant to multiple heavy metals and antibiotics. Majority of them were resistant to copper and bacitracin. Nine strains representing different resistance patterns were selected for plasmid profile and conjugation studies. Agarose gel electrophoresis results revealed that 6 strains harboured a single plasmid, whereas 3 strains exhibited 2 plasmid bands. Among antimicrobials, co-trimazole and bacitracin and among metals, Cu2+, Cd2+, Zn2+ and Ni2+ resistance were transferred most frequently at variable rates. However, chromium resistance was transferred in 6 strains with a frequency ranging 19-49x10(-2). Resistance to Co2+ and Hg2+ did not transfer under environmental conditions. Among the nine strains, three were found predominantly uropathogenic Escherichia coli (UPEC) serotype 04, whereas two strains were untypable. In addition, 4 transconjugants also showed a positive result after serotyping.