Chemical treatment of poultry litter affects the conjugation of plasmid-mediated extended-spectrum beta-lactamase resistance genes in E. coli

There is a general consensus among healthcare leaders that animal production industries should improve practices aiming to mitigate antimicrobial resistance, a significant global threat to public health. However, the epidemiology of antimicrobial resistance in animal production systems is very complex as a result of innumerous sources and dissemination routes of resistant bacteria. Furthermore, antimicrobial resistance can be transferred among bacteria by mobile elements, such as plasmids, which play a major role in the dissemination of antimicrobial resistance. In broiler production, litter contaminated by feces during the production cycle can serve as a potential reservoir for bacteria harboring antimicrobial resistance genes that can then be disseminated to susceptible bacteria. This study reports the effect of 1) different materials used as litter and 2) different litter recycling protocols on the conjugation frequencies of IncIII plasmids harboring extended-spectrum beta-lactamase-resistant genes among Escherichia coli isolates. Results found that, compared with cane bagasse litter, the use of wood shavings as litter decreased the conjugation frequency among E. coli isolates (P < 0.001). In regard to the recycling protocols, the presence of chemical residues in both types of litter materials was associated with a decreased conjugation frequency, with lowest frequencies observed for quicklime and superphosphate. Our findings suggest that the type of material used as poultry litter as well as litter recycling procedures, distinguished by means of chemical compounds, may affect plasmid conjugation among E. coli isolates.