Abstract:

Prevalence of antibiotic-resistant bacteria in wastewater effluents was concerned as an emerging contaminant. To estimate antibiotic resistance of bacteria in effluents of municipal wastewater treatment plants (WWTP), antibiotic tolerance, proportion of antibiotic-resistant bacteria, and hemi-inhibitory concentrations of six antibiotics (Penicillin, Cefalexin, Ciprofloxacin, Tetracycline, Gentamicin and Azithromycin) were determined at two wastewater treatment plants in Chengdu. The results showed that the total bacterial counts decreased along with the increase of antibiotic concentration, and the variations of Penicillin and Cefalexin were relatively higher than that of Tetracycline and Ciprofloxacin. Moreover, the concentrations of Ampicillin-resistant bacteria were highest to 6.5×104 and 7.2×104 CFU/mL in WWTP-A and WWTP-B, respectively, and the lowest antibiotic-resistant bacteria concentration was also as high as 8.9 CFU/mL. The hemi-inhibitory concentration of Gentamicin was highest in the 6 antibiotics, they were high to 28.1 mg/L and 25.4 mg/L in the two wastewater treatment plants. The data also indicated that the hemi-inhibitory concentrations of the bacteria to 6 antibiotics were much higher than common concentrations of antibiotics in sewages, which suggested that antibiotic-resistant bacteria could exist over a long period in the effluents with low concentrations of antibiotics．Antibiotic-resistant bacteria could be a potential microbial risk during sewage effluent reuse or emission into environmental waters.