Prevalence of ESBL-Producing Escherichia coli on Neck Skin in Slaughtered Broilers Raised on Conventional, Antibiotic-Free, and Organic Farms.

Antimicrobial resistance (AMR) among commensal Escherichia coli from poultry is a growing concern for food safety and public health. This study investigated AMR patterns in E. coli isolated from broiler neck skin at slaughter, comparing organic, antibiotic-free (ATB-free), and conventional production systems. A total of 375 samples were collected from two Italian slaughterhouses and tested by broth microdilution following EU protocols. E. coli was recovered from 358 samples, and 37.9% were presumptively positive for ESBL/AmpC-producing strains. Conventional broilers showed the highest resistance to ampicillin (73.8%), sulfonamides (72.5%), and fluoroquinolones (nalidixic acid, 62.5%; ciprofloxacin, 67.5%), while organic and ATB-free systems showed significantly lower levels. Intermediate resistance occurred for trimethoprim (21.4-47.9%) and tetracycline (36-54%), and low prevalence (<10%) was found for gentamicin, tigecycline, and third-generation cephalosporins. No relevant resistance was detected to colistin or carbapenems (≤1.2%). Total E. coli counts did not differ among systems, suggesting differences in resistant strain proportions rather than bacterial load. ATB-free flocks processed after conventional batches displayed higher resistance, indicating possible cross-contamination during slaughter. These results highlight the influence of farming practices and slaughterhouse hygiene on AMR dissemination, underscoring the need for integrated farm-to-slaughter control strategies.