Effect of ceftiofur cessation and substitution with lincomycin-spectinomycin on extended-spectrum-beta-lactamase/AmpC genes and multidrug resistance in E. coli from a Canadian broiler production pyramid

Ceftiofur, a cephalosporin antimicrobial, was used systematically in Canadian hatcheries for many years to prevent early mortality in chicks leading to a high prevalence of cephalosporin resistance in Escherichia coli in chickens. Preventive use of ceftiofur in hatcheries ceased in 2014. We examined the effect of ceftiofur cessation and replacement with lincomycin-spectinomycin at the hatchery on the proportion of E. coli positive for extended-spectrum {beta}-lactamase (ESBL) and AmpC {beta}-lactamase related genes, and on the multidrug resistance profiles of ESBL/AmpC positive E. coli in broilers and their associated breeders, at one year post-cessation. For indicator E. coli from non-enriched media, a significant decrease post-cessation in the proportion of samples harboring E. coli isolates positive for blaCMY-2 and/or blaCTX-M was observed. In contrast, following enrichment in medium containing ceftriaxone (1mg/L) to facilitate recovery of ESBL/AmpC {beta}-lactamase producing E. coli colonies, both pre- and post-cessation, 99% of the samples harbored E. coli positive for blaCMY-2 or blaCTX-M. Flocks receiving lincomycin-spectinomycin after cessation of ceftiofur showed a significantly greater non-susceptibility to aminoglycoside, folate inhibitor, phenicol, tetracycline and possible extensively drug resistant E. coli compared to those receiving ceftiofur or no antimicrobial at hatchery. This study clearly demonstrates an initial decrease in ESBL/AmpC positive E. coli following the cessation of ceftiofur in hatchery but an increase in multidrug resistant E. coli following replacement with lincomycin-spectinomycin.\n\nImportanceAntimicrobial resistance is a global problem. The antimicrobial ceftiofur has been used worldwide for disease prevention in poultry production resulting in a greatly increased resistance to this antimicrobial important in poultry and human medicine. Our study examines the impact of ceftiofur cessation and its replacement with the antimicrobial combination lincomycin-spectinomycin, a common practice in the industry. Our study demonstrated a decrease in ceftiofur resistance after the cessation of its use, although the resistance genes remain ubiquitous in all phases of poultry production, showing that poultry remains a reservoir for ceftiofur resistance and requiring continued vigilance. We also observed a decrease in multidrug resistance after cessation of ceftiofur although the contrary finding following use of lincomycin-spectinomycin indicates that the use of these antimicrobials should be questioned. Reduced resistance to ceftiofur in poultry may translate to better treatment efficacy, decreased morbidity, mortality, duration and cost of hospitalization in humans.