ABSTRACT: The wastewater of livestock slaughterhouses is considered a source of antimicrobial-resistant bacteria with clinical relevance and may thus be important for their dissemination into the environment. To get an overview of their occurrence and characteristics, we investigated process water (n = 50) from delivery and unclean areas as well as wastewater (n = 32) from the in-house wastewater treatment plants (WWTPs) of two German poultry slaughterhouses (slaughterhouses S1 and S2). The samples were screened for ESKAPE bacteria (Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp.) and Escherichia coli Their antimicrobial resistance phenotypes and the presence of extended-spectrum-β-lactamase (ESBL), carbapenemase, and mobilizable colistin resistance genes were determined. Selected ESKAPE bacteria were epidemiologically classified using different molecular typing techniques. At least one of the target species was detected in 87.5% (n = 28/32) of the wastewater samples and 86.0% (n = 43/50) of the process water samples. The vast majority of the recovered isolates (94.9%, n = 448/472) was represented by E. coli (39.4%), the A. calcoaceticus-A. baumannii (ACB) complex (32.4%), S. aureus (12.3%), and K. pneumoniae (10.8%), which were widely distributed in the delivery and unclean areas of the individual slaughterhouses, including their wastewater effluents. Enterobacter spp., Enterococcus spp., and P. aeruginosa were less abundant and made up 5.1% of the isolates. Phenotypic and genotypic analyses revealed that the recovered isolates exhibited diverse resistance phenotypes and β-lactamase genes. In conclusion, wastewater effluents from the investigated poultry slaughterhouses exhibited clinically relevant bacteria (E. coli, methicillin-resistant S. aureus, K. pneumoniae, and species of the ACB and Enterobacter cloacae complexes) that contribute to the dissemination of clinically relevant resistances (i.e., bla CTX-M or bla SHV and mcr-1) in the environment.IMPORTANCE Bacteria from livestock may be opportunistic pathogens and carriers of clinically relevant resistance genes, as many antimicrobials are used in both veterinary and human medicine. They may be released into the environment from wastewater treatment plants (WWTPs), which are influenced by wastewater from slaughterhouses, thereby endangering public health. Moreover, process water that accumulates during the slaughtering of poultry is an important reservoir for livestock-associated multidrug-resistant bacteria and may serve as a vector of transmission to occupationally exposed slaughterhouse employees. Mitigation solutions aimed at the reduction of the bacterial discharge into the production water circuit as well as interventions against their further transmission and dissemination need to be elaborated. Furthermore, the efficacy of in-house WWTPs needs to be questioned. Reliable data on the occurrence and diversity of clinically relevant bacteria within the slaughtering production chain and in the WWTP effluents in Germany will help to assess their impact on public and environmental health.
