Phenotypic and genotypic characteristics of beta-lactamase dominant with CARBA, AmpC, and ESBL-producing bacteria in municipal wastewater influent in Helsinki, Finland.

OBJECTIVES

Analysing samples of municipal wastewater influent (before treatment) can help to map the status of antibiotic-resistant bacteria (ARB) at the population level in sewershed communities and may also help in predicting the public health risks of ARB in surface water because of the outfall of wastewater. In this study, we investigated the bacterial isolates carrying beta-lactamase genes in wastewater and compared their genotypic and phenotypic characteristics.

METHODS

A total of 399 bacterial isolates grown on CHROMagarESBL (n = 207) and CHROMagarKPC (n = 192) from composite wastewater influent samples (n = 7) from the Viikinmäki wastewater treatment plant (Helsinki) were subcultured, nucleic acid was extracted, and the prevalence of different beta-lactamase genes was screened with multiplex polymerase chain reaction (PCR). All PCR-positive isolates were identified with MALDI-TOF.

RESULTS

A total of 32.6% of isolates (130 of 399) were PCR positive for at least one resistance gene, and 13% of these positive isolates out of 130 had at least three resistance genes. Among the 22 detected genes, blaGES group was the most prevalent, at 25.8% (n = 198; many isolates carried multiple genes), followed by blaMOX (13.1%) and blaTEM (10.1%) as most frequently detected. Furthermore, out of 18 different bacterial species/genera detected as carrying beta-lactamase genes, A. hydrophila/caviae (28.5%), Enterobacter spp. (16.9%), and E. coli (14.6%) were the most prevalent. Enterobacter spp., Aeromonas spp., and K. cryocescens potentially carried AmpC genes, and E. coli carried ESBL genes.

CONCLUSION

We recorded a huge variety of beta-lactamases (blaAmpC, blaESBL, and blaCARBA) genes in many potential pathogens that probably originated from both enteric and environmental sources.