Antibiotic-resistant bacteria, antibiotic resistance genes, and antibiotic residues in wastewater from a poultry slaughterhouse after conventional and advanced treatments

Slaughterhouse wastewater is considered a reservoir for antibiotic-resistant bacteria and antibiotic residues, which are not sufficiently removed by conventional treatment processes. This study focuses on the occurrence of ESKAPE bacteria (Enterococcus spp., S. aureus, K. pneumoniae, A. baumannii, P. aeruginosa, Enterobacter spp.), ESBL (extended-spectrum β-lactamase)-producing E. coli, antibiotic resistance genes (ARGs) and antibiotic residues in wastewater from a poultry slaughterhouse. The efficacy of conventional and advanced treatments (i.e., ozonation) of the in-house wastewater treatment plant regarding their removal was also evaluated. Target culturable bacteria were detected only in the influent and effluent after conventional treatment. High abundances of genes (e.g., bla$_{TEM}$, bla$_{CTX-M-15}$, bla$_{CTX-M-32}$, bla$_{OXA-48}$, bla$_{CMY}$ and mcr-1) of up to 1.48 × 10$^{6}$ copies/100 mL were detected in raw influent. All of them were already significantly reduced by 1–4.2 log units after conventional treatment. Following ozonation, mcr-1 and bla$_{CTX-M-32}$ were further reduced below the limit of detection. Antibiotic residues were detected in 55.6% (n = 10/18) of the wastewater samples. Despite the significant reduction through conventional and advanced treatments, effluents still exhibited high concentrations of some ARGs (e.g., sul1, ermB and bla$_{OXA-48}$), ranging from 1.75 × 10$^{2}$ to 3.44 × 10$^{3}$ copies/100 mL. Thus, a combination of oxidative, adsorptive and membrane-based technologies should be considered