Heavy Metal and Antibiotic Co-resistance in Bacteria Isolated from Poultry Samples in Bangladesh: An Emerging Environmental Threat

The excessive use of heavy metals and antibiotics as additives in livestock feed may significantly contribute to bacterial resistance in poultry environments by exerting selective pressure. This study aimed to comprehensively analyze bacterial isolates from poultry farms across Bangladesh, focusing on their resistance to heavy metals and antibiotics. Through microbial phenotypic screening, 23 cadmium-resistant and 28 chromium-resistant bacterial isolates were identified. The minimum inhibitory concentrations (MICs) for cadmium and chromium in metal-resistant bacterial isolates varied significantly, ranging from 200 μg/ml to 1600 μg/ml. All cadmium-resistant isolates were fully resistant to cefixime and ceftazidime, while chromium-resistant isolates showed 90% resistance to tetracycline. The cadmium resistance gene, such as czc , was detected in 26% (6/23) of cadmium-resistant isolates, and the chromium reductase gene chrR was detected in 18% (5/28) of chromium-resistant isolates. Among the chromium-reductase isolates, 40% (2/5) exhibited co-resistance and harbored the chrR gene, beta-lactam resistance genes ( bla-TEM , bla-NDM ), and the colistin resistance gene ( mcr-2 ). A significant association (p = 0.026) was observed between the presence of the chrR gene and these antibiotic resistance genes. However, no co-resistance was found in cadmium-resistant isolates. Mobile genetic elements, specifically Class 1 integrons, were found in 33.33% (2/6) of the isolates carrying the cadmium resistance gene ( czc ) and in 100% (5/5) of the isolates containing the chromium reductase gene ( chrR ). These findings underscore poultry environments in Bangladesh as significant reservoirs for bacteria with dual resistance to heavy metals and antibiotics, emphasizing the need for further investigation into the genetic mechanisms driving microbial resistance and its implications for public health.