Phenotypic and genotypic investigation of the heavy metal resistance in Escherichia coli isolates recovered from cattle stool samples

Abstract

The purpose of this study was to examine resistance against cadmium (Cd$^{+2}$), copper (Cu$^{+2}$), lead (Pb$^{+2}$), mercury (Hg$^{+2}$), and manganese (Mn$^{+2}$) in Escherichia coli isolates recovered from cattle stool using phenotypic (agar dilution) and genotypic [polymerase chain reaction (PCR)] methods. In addition, the isolates were genotyped via enterobacterial repetitive intergenic consensus polymerase chain reaction (ERIC-PCR). Escherichia coli was isolated and identified from the 100 stool samples that were examined in the study. It was determined phenotypically that all isolates were sensitive to mercury; 97% of them showed resistance to cadmium; 69% showed resistance to copper; 24% showed resistance to lead; and 20% showed resistance to manganese. In the isolates found resistant by phenotypic method, the presence of the zntA gene provided common resistance for Cd$^{+2}$ and Pb$^{+2}$; pcoR gene provided resistance for Cu$^{+2}$; and mntR gene for Mn$^{+2}$ in both genomic DNA and plasmid DNA. Since all isolates were sensitive to Hg$^{+2}$, the presence of merA gene was not examined. While the target genes that were examined for lead, cadmium, and manganese were detected in all isolates, the pcoR gene for copper was detected in 53.6% of the phenotypic-resistant isolates. As a result of the statistical analysis, it was determined that the phenotypic resistance rates of the isolates did not vary according to age group, county, or city at a significant level (P > 0.05). The high metal resistance detected in the present study led us to conclude that heavy metal contamination around cattle farms may be common. Metals are used as an additive substance in animal husbandry. Using the correct fertilizer to minimize contamination sources or limiting the use of materials that contain metals may be useful, and new legal rules may be required.