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 A 2 O 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.
Highlights
The overuse of antibiotics in medicine and agriculture caused a reduction of their efficacy against most of infectious diseases
The highest average values of biochemical oxygen demand over days (BOD) in untreated wastewater (UWW) were found in samples from wastewater treatment plants (WWTPs) in group B (606 mg/L), while the lowest were found in samples from WWTPs belonging to group A (401 mg/L)
The highest values of chemical oxygen demand (COD) were observed among UWW samples from WWTPs belonging to group D (1540 mg/L), whereas the lowest were found in UWW samples from WWTPs of group C (1199 mg/L)
Summary
The overuse of antibiotics in medicine and agriculture caused a reduction of their efficacy against most of infectious diseases. According to the World Health Organization (WHO), the increase of antibiotic resistance among bacteria is one of the most important global problems [1]. According to the report prepared by O’Neill [2] due to infections caused by bacteria resistant to antimicrobial agents, 700,000 people die every year, and by 2050 this number is expected to grow to over 10 million. The definition of drug-resistant bacteria given by ECDC [3] is based on the limit values relating to the clinical strains. That is why it seems necessary to have an alternative approach to the microbial characteristics of environmental strains [4]. There is no exhaustive data allowing to assess the consequences of the occurence of antibiotic resistance in environmental bacteria
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