Monitoring of drug resistance amplification and attenuation with the use of tetracycline-resistant bacteria during wastewater treatment

¹ Department of Environmental Microbiology, University of Warmia and Mazury in Olsztyn, ul. Prawocheńskiego 1, 10-957 Olsztyn, Poland
² Department of Food and Industrial Microbiology, University of Warmia and Mazury, Plac Cieszyński 1, 10-726 Olsztyn, Poland

^* Corresponding author: monika.harnisz@uwm.edu.pl

Abstract

The objective of this study was to monitor changes (amplification or attenuation) in antibiotic resistance during wastewater treatment based on the ecology of tetracycline-resistant bacteria. The untreated and treated wastewater were collected in four seasons. Number of tetracycline-(TET^R) and oxytetracycline-resistant (OTC^R) bacteria, their qualitative composition, minimum inhibitory concentrations (MICs), sensitivity to other antibiotics, and the presence of tet (A, B, C, D, E) resistance genes were determined. TET^R and OTC^R counts in untreated wastewater were 100 to 1000 higher than in treated effluent. OTC^R bacterial counts were higher than TET^R populations in both untreated and treated wastewater. TET^R isolates were not dominated by a single bacterial genus or species, whereas Aeromonas hydrophila and Aeromonas sobria were the most common in OTC^R isolates. The treatment process attenuated the drug resistance of TET^R bacteria and amplified the resistance of OTC^R bacteria. In both microbial groups, the frequency of tet(A) gene increased in effluent in comparison with untreated wastewater. Our results also indicate that treated wastewater is a reservoir of multiple drug-resistant bacteria as well as resistance determinants which may pose a health hazard for humans and animals when released to the natural environment.