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Abstract
Due to the high prevalence of colistin-resistant Enterobacteriaceae in poultry and pigs, process waters and wastewater from slaughterhouses were considered as a hotspot for isolates carrying plasmid-encoded, mobilizable colistin resistances (mcr genes). Thus, questions on the effectiveness of wastewater treatment in in-house and municipal wastewater treatment plants (WWTPs) as well as on the diversity of the prevailing isolates, plasmid types, and their transmissibility arise. Process waters and wastewater accruing in the delivery and unclean areas of two poultry and two pig slaughterhouses were screened for the presence of target colistin-resistant bacteria (i.e., Escherichia coli, Klebsiella spp., Enterobacter cloacae complex). In-house and municipal WWTPs (mWWTPs) including receiving waterbodies were investigated as well. Samples taken in the poultry slaughterhouses yielded the highest occurrence of target colistin-resistant Enterobacteriaceae (40.2%, 33/82), followed by mWWTPs (25.0%, 9/36) and pig slaughterhouses (14.9%, 10/67). Recovered isolates exhibited various resistance patterns. The resistance rates using epidemiological cut-off values were higher in comparison to those obtained with clinical breakpoints. Noteworthy, MCR-1-producing Klebsiella pneumoniae and E. coli were detected in scalding waters and preflooders of mWWTPs. A total of 70.8% (46/65) of E. coli and 20.6% (7/34) of K. pneumoniae isolates carried mcr-1 on a variety of transferable plasmids with incompatibility groups IncI1, IncHI2, IncX4, IncF, and IncI2 ranging between 30 and 360 kb. The analyzed isolates carrying mcr-1 on transferable plasmids (n = 53) exhibited a broad diversity, as they were assigned to 25 different XbaI profiles. Interestingly, in the majority of colistin-resistant mcr-negative E. coli and K. pneumoniae isolates non-synonymous polymorphisms in pmrAB were detected. Our findings demonstrated high occurrence of colistin-resistant E. coli and K. pneumoniae carrying mcr-1 on transferrable plasmids in poultry and pig slaughterhouses and indicate their dissemination into surface water.
Highlights
IntroductionSince the 1950s, colistin (polymyxin E) has been extensively used in the European animal production (Koyama et al, 1950) to prevent and treat gastrointestinal infections caused by Gram-negative bacteria (e.g., diarrhea in pigs caused by Escherichia coli and Salmonella spp. as well as colibacillosis in poultry) (EMEA, 2002)
Since the 1950s, colistin has been extensively used in the European animal production (Koyama et al, 1950) to prevent and treat gastrointestinal infections caused by Gram-negative bacteria (EMEA, 2002)
Our study provides data on the occurrence of colistin resistant Enterobacteriaceae (E. coli, K. pneumoniae, and E. cloacae complex) in process waters and wastewater along the slaughtering processes in poultry and pig slaughterhouses, their in-house and municipal WWTPs (mWWTPs) as well as receiving waterbodies
Summary
Since the 1950s, colistin (polymyxin E) has been extensively used in the European animal production (Koyama et al, 1950) to prevent and treat gastrointestinal infections caused by Gram-negative bacteria (e.g., diarrhea in pigs caused by Escherichia coli and Salmonella spp. as well as colibacillosis in poultry) (EMEA, 2002). It was used in a lower dosage as a feed additive until the ban of antimicrobial growth promoters in the European Union (EU) in 2006 (EMA, 2016). From 2016 its sales have been slightly increasing and reached 74 tons in 2018 making up 10.2% of the total amount of antimicrobials sold for the veterinary use in Germany (BVL, 2019)
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