Impact of various pig husbandry conditions on antimicrobial resistance

Citation

Poulin-Laprade et al. (2021) Impact of various pig husbandry conditions on antimicrobial resistance. 5th international conference on Responsible Use of Antibiotics in Animals, Towards Sustainable Solutions Amsterdam Virtual 2021/06/08

Plain language summary

Pigs are major reservoirs of resistant bacteria that can reach humans through consumption of contaminated meat or vegetables grown in manure-fertilized soil. We collected and analysed samples from pigs reared with conventional and antibiotic-free practices to assess the impact of antibiotics use in feed on the fecal load in antimicrobial resistance. We found that a critical threat to humain health, namely the extended spectrum β-lactamase (ESBL) phenotype, was more frequent in isolates originating from antibiotic-free animals, while the bacteria isolated from penicillin-using animals were on average resistant to a greater number of antibiotics. Most resistance determinants were shared by animals raised with or without antimicrobials. This suggests a key contribution of indigenous enterobacteria maternally transmitted along the sow lineage, regardless of antimicrobial use. It is unclear if the antimicrobial resistance observed in the enterobacteria populations of the commercial pig herds studied were present before the use of antibiotics, or the extent to which historical antimicrobial use exerted a selective pressure defining the resistant bacterial populations in farms using the antibiotic penicillin.

Abstract

Pigs are major reservoirs of resistant Enterobacteriaceae that can reach humans through consumption of contaminated meat or vegetables grown in manure-fertilized soil. Samples were collected from sows during lactation and their piglets at five time points spanning the production cycle. Cefotaxime-resistant bacteria were quantified and isolated from feed, feces, manures and carcasses of pigs reared with penicillin-using or antibiotic-free husbandries. The isolates were characterized by antibiotic susceptibility testing, whole genome sequencing and conjugation assays. The extended spectrum β-lactamase (ESBL) phenotype was more frequent in isolates originating from antibiotic-free animals, while the bacteria isolated from penicillin-using animals were on average resistant to a greater number of antibiotics. The ESBL-encoding genes identified were blaCTX-M-1, blaCTX-M-15 and blaCMY-2 and they co-localised on plasmids with various genes encoding resistance to ß-lactams, co-trimoxazole, phenicols and tetracycline, all antibiotics used in pig production. Most resistance determinants were shared by animals raised with or without antimicrobials. This suggests a key contribution of indigenous enterobacteria maternally transmitted along the sow lineage, regardless of antimicrobial use. It is unclear if the antimicrobial resistance observed in the enterobacteria populations of the commercial pig herds studied were present before the use of antibiotics, or the extent to which historical antimicrobial use exerted a selective pressure defining the resistant bacterial populations in farms using penicillin prophylaxis.