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

Objective: Analyzing 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 due to the outfall of wastewater. In this study, we investigated the bacterial isolates carrying beta-lactamase (BL) 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 sub-cultured, nucleic acid was extracted, and the prevalence of different BL 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 out 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, bla_{GES group} was the most prevalent, at 25.8% (n = 198; many isolates carried multiple genes), followed by bla_MOX (13.1%), and bla_TEM (10.1%) as most frequently detected. Furthermore, out of 18 different bacterial species/genera detected as carrying BL genes, A. hydrophila/caviae (28.5%), Enterobacter spp. (16.9%), and E. coli (14.6%) were the most prevalent. Enterobacter spp., Aeromonas spp., K. cryocescens potentially carried AmpC genes and E. coli carried ESBL genes.

Conclusion: We recorded a huge variety of bla_BL(bla_AmpC, bla_ESBL and bla_CARBA) genes in many potential pathogens that probably originated from both enteric and environmental sources.