High diversity of extended-spectrum beta-lactamases in Escherichia coli isolates from Italian broiler flocks

Abstract

We characterized 67 Escherichia coli isolates with reduced susceptibility to cefotaxime or ceftiofur obtained from healthy broilers housed in five Italian farms. The bla(CTX-M-1), bla(CTX-M-32) and bla(SHV-12) beta-lactamase genes were identified on IncI1, IncN, or IncFIB plasmids. Considerable genetic diversity was detected among the extended-spectrum beta-lactamase (ESBL)-producing isolates, and we identified indistinguishable strains in unrelated farms and indistinguishable plasmids in genetically unrelated strains. The detection of highly mobile plasmids suggests a potential animal reservoir for beta-lactamase genes.

FIG. 1.

Dendrogram showing the genotypic relatedness of 67 Escherichia coli isolates based on AFLP fingerprints. A Dice coefficient and the unweighted-pair group method using average linkages (UPGMA) algorithm were used with a position tolerance of 1%. The scale bar represents the percentage of similarity, and the vertical, dotted line indicates the cutoff value for identifying clonal types. PBRT, plasmid-based replicon typing as determined with a subset of isolates indicated by gray-shaded ovals.