Isolation and characterization of ESKAPE-bacteria and ESBL-producing E. coli from waste- and process water of German poultry slaughterhouses.

Wastewater of livestock slaughterhouses is being considered as a source of antimicrobial-resistant bacteria with clinical relevance and may thus be important for their dissemination into the environment. To get an overview on their occurrence and characteristics, we have investigated process water (n=50) from delivery and unclean areas as well as wastewater (n=32) from in-house wastewater treatment plants of two German poultry slaughterhouses (S1, 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, ESBL (extended spectrum β-lactamase), 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 waste- 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%), A. calcoaceticus-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, MRSA, K. pneumoniae, species of the ACB-and E. cloacae-complexes) that contribute to the dissemination of clinically relevant resistances (i.e. blaCTX-M/SHV, 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 both in veterinary and human medicine. They may be released into the environment from wastewater treatment plants (WWTPs) that are influenced by wastewater from slaughterhouses, thereby endangering public health. Moreover, process water that accumulates during slaughtering of poultry is an important reservoir for livestock-associated multidrug-resistant bacteria and may serve as a transmission vector to occupationally exposed slaughterhouse employees. Mitigation solutions aiming at the reduction of the bacterial discharge into the production water circuit as well as intervention of 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 slaughtering production chain and in the WWTPs effluents in Germany will help to assess their impact on public and environmental health.