Quantifying transfer dynamics of ESBL/pAmpC E. coli across the broiler production pyramid

This study aimed to establish baseline prevalence data for extended-spectrum β-lactamase (ESBL)- and pAmpC-producing E. coli (ESBL/pAmpC-EC) and to quantify its stepwise transfer in Italy’s broiler production pyramid. Three production chains of an integrated broiler company were investigated. Cloacal swabs were taken from Parent Stock (PS) chickens and the offspring broiler flocks in 4 fattening farms per chain. Carcasses from the sampled broiler flocks were collected at slaughterhouse. Samples were processed on Eosin Methylene Blue agar with 1mg/L cefotaxime (CTX-EMB) and typical E. coli growing on CTX-EMB were screened for ESBL/pAmpC production by disk diffusion. Moreover, ESBL/pAmpC genes were detected by PCR and sequencing. The average pairwise overlap of ESBL/pAmpC-EC gene occurrences between subsequent production stages was estimated using the proportional similarity index (PSI), modelling both uncertainty and variability in a Monte Carlo simulation. A total of 820 samples were processed from which 513 ESBL/pAmpC-EC isolates were obtained. We found a high prevalence (92.5%, 95%CI 78.9-97.6%) in one-day-old PS chicks, where blaCMY genes predominated, dropped significantly to 20% (11.7-32.1%) at laying period. In fattening broilers, prevalence was 69.2% (57.5-78.7%) at the start of production, 54.2% (35.1-72.1%) before slaughter, and 61.2% (55.6-66.6%) in carcasses. Significantly decreasing and increasing trends for blaCMY and blaCTX-M-group-1 gene occurrences were respectively found across subsequent production stages. The estimated average stepwise transfer of ESBL/pAmpC-EC genes between subsequent production stages was 47.7% (42.3-53.4%). These quantitative data can provide new insights for ESBL/pAmpC-EC risk-mitigating strategies across the broiler production pyramid.