Prevalence and Characterization of Cephalosporin Resistance in Nonpathogenic Escherichia coli from Food-Producing Animals Slaughtered in Poland

The prevalence of Escherichia coli with putative extended-spectrum cephalosporin resistance was assessed in cattle, pigs, broilers, layers, and turkey slaughtered in Poland. The occurrence of random E. coli isolates recovered from MacConkey agar plates with non–wild-type minimal inhibitory concentrations for cefotaxime and ceftazidime reached 0.6% in layers, 2.3% in turkey, and 4.7% in broilers, whereas all cattle and pigs isolates fell into the wild-type subpopulation.

The use of MacConkey agar supplemented with cefotaxime (2 mg/L) increased the recovery of resistant strains up to 33.3% of samples from pigs, 42.3% from layers, 48.0% from turkey, and 54.5% from broilers. Still, no cephalosporin-resistant E. coli was found in cattle. E-test identified extended-spectrum beta-lactamase (ESBL) and ampC-type resistance phenotypes in 15 and 33 strains, respectively.

Molecular characterization identified CTX-M-1 gene in 13 ESBL strains, 5 of which possessed also TEM-1b. One strain harbored SHV-12 gene. CMY-2 was found in all of 20 tested ampC-type cephalosporinase-positive strains either alone (n = 14) or in combination with mutations in ampC promoter region (n = 6).

CTX-M-1 and CMY-2 genes were noted also in five strains from laying hens and broilers originated from Belgium and Germany. Nosocomial infections in Poland are caused by E. coli carrying other determinants than those found in our study. Thus, our results indicate that animals colonized with cephalosporin-resistant strains might not be the major source of human infections in Poland.

However, the contribution to community-acquired infections by spread of resistant clones or resistance genes may not be excluded.