Occurrence of extended-spectrum beta-lactamases in Salmonella enterica strains isolated from broilers and food of animal origin in Portugal

Salmonella enterica is a zoonotic bacteria transmitted through the food chain and isolates harbouring extended-spectrum beta-lactamases (ESBLs) have emerged worldwide during the last decade, with the CTX-M group being particularly important. The aim of the present study was to determine the antimicrobial susceptibility of S. enterica strains isolated from broilers and food of animal origin and to characterize ESBLs producers. On the scope of the national antimicrobial resistance surveillance programme on Salmonella, a total of 283 strains isolated from broilers (n=100) and food of animal origin (n=183), were received at the National Laboratory of Veterinary Research in 2011. The minimum inhibitory concentration (MIC) of 11 antimicrobials (nalidixic acid, ciprofloxacin, ampicillin, cefotaxime, chloramphenicol, florfenicol, streptomycin, gentamicin, tetracycline, sulphamethoxazole and trimethoprim) for all isolates was determined by agar dilution method. Susceptibility towards cefoxitin was determined through disk diffusion method. Breakpoints were interpreted accordingly to EUCAST epidemiological cut-off values. ‘Non-wild type’ (‘NWT’) isolates for cefotaxime (MIC>0.5mg/L) and cefoxitin (