The influence of antibiotics, namely doxycycline, gentamicin, penicillin, nitrofurantoin, and rifampicin, on wastewater treatment was assessed. The presence of 100–300 μg/L of antibiotics (63.52–134.41 mg/g.d.w·d) marginally influenced organic matter degradation, without impacting nitrogen or phosphorus concentrations. However, a significant increase in the number of antibiotic-resistant bacteria was observed, which varied with different antibiotics. The largest number of bacteria became resistant to nitrofurantoin and penicillin. After the process, some multi-resistant strains were isolated from the sludge. Two of them revealed the activity of carbapenamase, the enzyme directly related to resistance against β-lactam antibiotics.