Beta-lactamase-producing Enterobacteriaceae in hospital effluents

Beta-lactams are widely used to treat bacterial infections in humans. In most countries, they are the largest group of antibiotics used by hospitals to treat infections caused by Gram-negative bacteria. Enterobacteriaceae, natural microbiota of the human gastrointestinal tract, represent a large part of bacterial communities colonizing hospital effluents, and they could be a source of genes encoding beta-lactamases and extended-spectrum-beta-lactamases (ESBLs). Those genes may be transmitted to other bacteria present in sewage and the environment. The prevalence of ESBL-producing Enterobacteriaceae was investigated in 63 sewage samples from three hospitals in Olsztyn, Poland. In the group of 310 randomly sampled strains isolated from hospital effluents, 295 (95.2%), 253 (81.6%) and 228 (73.5%) isolates were resistant to cefotaxime, ceftazidime and cefpodoxime, respectively. 150 of them were phenotypically ESBL-positive, but only 91 (29.4%) of those isolates harbored ESBL-genes. In the group of ESBL-producers, 54.9% (50/91), 39.6% (36/91), 24.2% (22/91) and 11.0% (10/91) carried blaCTx-M group 1, blaCTx-M group 9, blaSHV and blaTEM genes, respectively. More than 27.5% (25/91) of the analyzed isolates carried up to three bla genes. High minimum inhibitory concentration (MIC) values of cefotaxime and ceftazidime (≥512 μg/mL) were observed for the studied microorganisms. Escherichia coli and Citrobacter freundii were the most frequently identified ESBL-positive strains. A statistically significant correlation was observed between antibiotics consumption in each hospital and the incidence of ESBL-positive isolates in hospital effluents.