Quantification, distribution and diversity of ESBL/AmpC-producing Escherichia coli on freshly slaughtered pig carcasses

This study quantified cefotaxime-resistant E. coli (CREC) on nine different carcass areas of 104 freshly slaughtered pig carcasses. In 49% [95% confidence interval (95% CI): 29-69%] of the carcasses CREC could be isolated and enumerated (using Tryptone Bile Agar with X-Glucuronide supplemented with 1 mg/L cefotaxime). Proportions of positive samples varied between carcass areas from 1% [95% CI: 0-10%] (loin) to 23% [95% CI: 10-44%] (head). Maximum concentrations on positive samples ranged between -0.6 log₁₀ CFU/cm² (loin, elbow before evisceration) and 1.7 log₁₀ CFU/cm² (head). The head was significantly more frequently contaminated than the loin (p = 0.027) and ham (3% [95% CI: 1-15%]). The foreleg was significantly more frequently contaminated (20% [95% CI: 13-30%]) than the ham. Combination disk diffusion assays revealed that 81% of the CREC isolates were extended-spectrum beta-lactamases (ESBL) producers, 13% were AmpC cephalosporinases (AmpC) producers and 2% ESBL and AmpC co-producers. Genotyping denoted bla_CTX-M-gr1 (63%) and bla_TEM (40%) as most present antibiotic resistance genes. Multiple gene combinations in one isolate and multiple combinations of genotypes and phenotypes among isolates of one sample were observed. These quantitative data can be used for intervention strategies to lower human exposure to CREC.