Prevalence of Heavy Metal and Antibiotic Resistance in Bacterial Isolates from Metal Polluted Soils

Abstract

Owing to continual industrialization and exploitation of metal-containing agricultural products in current farming practices, environmental pollution is burgeoning with the release of toxic metal species and antibiotic products and concomitantly affecting both soil health and water quality. Therefore, this study was undertaken to determine the level of heavy metal and antibiotic resistance patterns in bacterial isolates from agricultural soils irrigated with metal polluted wastewater. A total of 34 bacteria isolates were recovered from soils and characterized as pseudomonads (67%), bacilli (15%) and staphylococci (18%) following standard methods. Further, resistance of bacterial isolates to heavy metals and antibiotics was determined by the plate dilution and disc diffusion methods, respectively. This study showed that 14.7% isolates were resistant to Hg2+, 2.9%-Cd2+, 91.2%-Cu2+, 79.5%-Zn2+, 91.2%-Ni2+, 97%-Pb2+, 94.1%-Cr3+ and 79.4%-Cr6+. Furthermore, all bacterial isolates showed resistance to one to eight antibiotics in different combinations and more than 80% isolates exhibited resistance to neomycin, cloxacillin and amoxicillin. Bacterial isolates possessing co-resistance to the maximum number of heavy metals as well as exhibiting multiple antibiotic resistance patterns were found to harbor plasmid DNA. The results of this study inferred that the agricultural soil irrigated with metal polluted wastewater is a rich source of resistant bacteria to heavy metals and antibiotics and bacteria isolated from these sites have substantial resistance to both heavy metals and antibiotics. Moreover, these sites may be exploited to isolate the multiple metal and antibiotic resistant bacteria of environmental significance.