## 4 Discussion  
Wastewater treatment plants constitute a potential source of ARB and ARGs, which can be transmitted to the environment with discharged treated wastewater. For this reason, monitoring microbiological pollutant removal effectiveness during wastewater treatment is of particular significance. Results of studies on the number of antibiotic resistant bacteria on culture media were published by [PERSON] et al. [29]. Based on these results, the most frequently occurring bacteria were those that were resistant to amoxicillin and oxytetracycline, i.e., older generation antibiotics. Even though wastewater treatment plants usually ensured a rather high level of reduction in the number of antibiotic-resistant bacteria (at least 99.9%), treated wastewater from WWTPs that were discharged to the environment contained, on average, from 1.05 \(\times\) 10\({}^{2}\) to 2.77 \(\times\) 10\({}^{5}\) CFU/mL. It should be stressed that the percentage of antibiotic-resistant bacteria in the total number of microorganisms increased following the wastewater treatment process. Genes that are responsible for resistance to beta-lactam antibiotics were reduced to a greater extent following the wastewater treatment process as compared to the number of genes responsible for resistance to tetracyclines. [PERSON] et al. [6] also found that, despite a reduction by as much as 78% in the total number of bacteria following the wastewater treatment process, a reduction in ARGs concentration was not always observed. Moreover, the occurrence of multi-drug resistant bacteria was found. [PERSON] et al. [31] demonstrated that the concentration of _blat_CTX-M, _blat_TEM, and _qnrS_ genes relative to the number of copies of 165 _r_RNA was generally similar in the samples of wastewater both before and after the treatment process. The authors also demonstrated that in wastewater from the treatment plant receiving mixed municipal and hospital wastewater, the concentration of genes increased following the treatment process. In wastewater from a biological treatment plant using disinfection with UV radiation, there was also no reduction in the concentrations of _blat_TEM, _qnrA_, and _sull_ genes in the samples of treated wastewater from that WWTP. [PERSON] et al. [23] noted that the relative concentrations of _ernB_ and _tetW_ genes decreased as a result of wastewater treatment, while the concentration of _blat_TEM, _sul1_, and _qnrS_ genes in wastewater increased. Those authors also demonstrated that the incomplete removal of antibiotics and ARGs in the wastewater treatment process significantly affected the water quality of the river receiving treated wastewater. This was because the concentration of antibiotics and ARG concentrations at a point beyond the wastewater inflow were higher than in the samples collected before the effluent discharge point. Other study results [24; 25] also confirm the ineffective elimination of ARGs by conventional wastewater treatment plants. They also indicate that the bacteria released with wastewater from WWTPs may be capable of actively spreading the resistance genes among the local microorganisms, thus inhabiting ecosystems of surface water bodies that receive treated wastewater. The present study demonstrated that for the genes responsible for resistance to tetracyclines in all tested WWTPs, both in the total bacterial population and in _E. coli_ population, the _tet_A gene occurred at higher concentrations than the _tet_M gene. [PERSON] et al. [18]. in their study concerning the change in microorganism communities of the activated sludge and ARGs under selection pressure of antibiotics in SBR reactors, observed that the total number of ARGs in the activated sludge increased following the addition of tetracycline (TC). This indicates that bacteria with ARGs proliferate intensively under the pressure of antibiotic presence.