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

The development of multiple metal/antibiotic resist ances among the bacterial population causes a poten tial risk to human health. Metal contamination in natura l environments could have an important role in the maintenance and proliferation of antibiotic resista nce. In the present study, a total of 46 heterotrop hic bacterial isolates from metal contaminated soil were tested f or their sensitivity to 10 widely used antibiotics such as ampicillin, erythromycin, gentamicin, nalidixic aci d, penicillin, amikacin, lincomycin, novobiocin, va ncomycin and tetracycline. Metal tolerant ability of these iagainst five heavy metals such as lead, zin c, copper, cadmium and nickel were also determined. The result s revealed that most of the bacterial isolates were resistant to one or more heavy metals/ antibiotics against wh ich they are tested. Tolerance to heavy metal showe d 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 isol ates were resistant to amikacin, while resistance to gen tamicin and tetracycline were low (2.17%). Out of the 46 bacterial isolates, 36 isolates showed multiple met al and antibiotic resistances. Isolate LOC 10 showe d significantly high tolerance (100-300ug/mL) to all the metals and was resistant to 6 antibiotics.