Impact of type of wastewater treatment process on the antibiotic resistance of bacterial populations

Abstract

Antibiotic resistant bacteria reach the environment directly with faeces, and indirectly with sewage discharged from wastewater treatment plants (WWTPs). The aim of the study was to determine the level of removal of bacteria during wastewater treatment. Samples of untreated and treated sewage were collected from 13 WWTPs with different capacity, modification of treatment and type of inflowing wastewater. Microbiological characterization of the samples included determination of the total number of bacteria resistant (ARB) to β-lactams and tetracyclines as well as the number of Escherichia coli resistant to the same drugs. The counts of ARB and E. coli were determined on TSA and mFc media with/without antibiotic supplementation, respectively. The highest percent of reduction in number of ARB (at least 99.9%) and E. coli (above 99.3%) was obtained for WWTPs with A2O system. The lowest percentage reduction of ARB and E. coli was observed for WWTPs operating with SBR system. The lowest number of microorganisms resistant to analyzed antibiotics was observed for ARB and E. coli resistant to cefotaxime and doxycycline. The results indicate a large variation in the removal of antibiotic-resistant bacteria in WWTPs depending on modifications of treatment system and type of inflowing wastewater.