Heavy metal tolerance and multiple drug resistance of heterotrophic bacterial isolates from metal contaminated soil

Abstract

The development of multiple metal/antibiotic resistances among the bacterial population causes a potential risk to human health. Metal contamination in natural environments could have an important role in the maintenance and proliferation of antibiotic resistance. In the present study, a total of 46 heterotrophic bacterial isolates from metal contaminated soil were tested for their sensitivity to 10 widely used antibiotics such as ampicillin, erythromycin, gentamicin, nalidixic acid, penicillin, amikacin, lincomycin, novobiocin, vancomycin and tetracycline. Metal tolerant ability of these isolates against five heavy metals such as lead, zinc, copper, cadmium and nickel were also determined. The results revealed that most of the bacterial isolates were resistant to one or more heavy metals/ antibiotics against which they are tested. Tolerance to heavy metal showed the following pattern; lead > zinc > nickel > copper > cadmium. Resistance to ampicillin (73.91%), penicillin (60.8%), lincomycin (43.47%) and nalidixic acid (21.73%) were encountered frequently. None of the isolates were resistant to amikacin, while resistance to gentamicin and tetracycline were low (2.17%). Out of the 46 bacterial isolates, 36 isolates showed multiple metal and antibiotic resistances. Isolate LOC 10 showed significantly high tolerance (100-300�g/mL) to all the metals and was resistant to 6 antibiotics.