Prevalence of Beta Lactamases Genes in Sewage and Sludge Treated in Mechanical-Biological Wastewater Treatment Plants

Wastewater treatment plants (WWTPs) are a very important link in the spread of antibiotic resistance genes to the environment and the formation of antibiotic-resistant microorganisms. The mechanical and biological methods of wastewater treatment in WWTPs do not completely remove the resistance genes from sewage. The genes responsible for extended-spectrum beta-lactamases (ESBLs) are very common in the family Enterobacteriaceae that colonize the human digestive tract and are abundant in wastewater. The aim of this study was to analyze the prevalence of genes encoding beta-lactamases in the wastewater and sludge samples collected from two WWTPs in the Polish regions of Warmia and Silesia and from the river water upstream and downstream from the WWTPs. The wastewater samples were passed through polycarbonate membrane filters, whereas the sludge samples were homogenized, and genomic DNA was extracted. The bla_TEM, bla_OXA and bla_SHV genes were detected by means of standard PCR. The most prevalent gene was bla_TEM which occurred in all samples, including the treated wastewater. The bla_OXA gene was also frequently detected in all samples from the WWTP in Silesia. The bla_SHV gene was least prevalent in the tested samples. These results indicate that wastewater is a hotspot for resistant bacteria. Beta-lactamase genes are not eliminated through the mechanical-biological wastewater treatment methods, and they can spread to other environments, thus increasing the pool of antibiotic resistance genes around the world and creating epidemiological risks.