Bacterial Resistance to β-Lactam Antibiotics in Municipal Wastewater: Insights from a Full-Scale Treatment Plant in Poland

This study investigated enzymatic and genetic determinants of bacterial resistance to β-lactam antibiotics in the biocenosis involved in the process of biological treatment of wastewater by activated sludge. The frequency of bacteria resistant to selected antibiotics and the activity of enzymes responsible for resistance to β-lactam antibiotics were estimated. The phenomenon of selection and spread of a number of genes determining antibiotic resistance was traced using PCR and gene sequencing. An increase in the percentage of bacteria showing resistance to β-lactam antibiotics in the microflora of wastewater during the treatment process was found. The highest number of resistant microorganisms, including multi-resistant strains, was recorded in the aeration chamber. Significant amounts of these bacteria were also present in treated wastewater, where the percentage of penicillin-resistant bacteria exceeded 50%, while those resistant to the new generation β-lactam antibiotics meropenem and imipenem were found at 8.8% and 6.4%, respectively. Antibiotic resistance was repeatedly accompanied by the activity of enzymes such as carbapenemases, metallo-β-lactamases, cephalosporinases and β-lactamases with an extended substrate spectrum. The activity of carbapenemases was shown in up to 97% of the multi-resistant bacteria. Studies using molecular biology techniques showed a high frequency of genes determining resistance to β-lactam antibiotics, especially the blaTEM1 gene. The analysis of the nucleotide sequences of blaTEM1 gene variants present in bacteria at different stages of wastewater treatment showed 50–100% mutual similarity of.