Limited Dissemination of Extended-Spectrum β-Lactamase- and Plasmid-Encoded AmpC-Producing Escherichia coli from Food and Farm Animals, Sweden

Abstract

Extended-spectrum β-lactamase (ESBL)- and plasmid-encoded ampC (pAmpC)-producing Enterobacteriaceae might spread from farm animals to humans through food. However, most studies have been limited in number of isolates tested and areas studied. We examined genetic relatedness of 716 isolates from 4,854 samples collected from humans, farm animals, and foods in Sweden to determine whether foods and farm animals might act as reservoirs and dissemination routes for ESBL/pAmpC-producing Escherichia coli. Results showed that clonal spread to humans appears unlikely. However, we found limited dissemination of genes encoding ESBL/pAmpC and plasmids carrying these genes from foods and farm animals to healthy humans and patients. Poultry and chicken meat might be a reservoir and dissemination route to humans. Although we found no evidence of clonal spread of ESBL/pAmpC-producing E. coli from farm animals or foods to humans, ESBL/pAmpC-producing E. coli with identical genes and plasmids were present in farm animals, foods, and humans.

Keywords: ESBL; Escherichia coli; Sweden; antimicrobial resistance; bacteria; bloodstream infections; broilers; carriage; extended-spectrum cephalosporin; extended-spectrum β-lactamase; farm animals; foodborne infections; meat; national assessment; pAmpC; plasmid-encoded AmpC; poultry.

Figure 1

Frequency of overlapping extended-spectrum β-lactamase– and plasmid-encoded AmpC genes in Escherichia coli isolates from various sources, Sweden. Data for leafy greens were excluded because there were only 2 isolates (both bla_CTX-M-1) from this source.

Figure 2

Frequency of overlapping plasmid replicon types containing extended-spectrum β-lactamase– and plasmid-encoded AmpC genes in Escherichia coli isolates from various sources, Sweden. Data for leafy greens were excluded because there were only 2 isolates (incI1 and incI2). Other replicon types also include nontypeable plasmids. Gray bar indicates plasmids that could not be transferred by electroporation, primarily isolates with bla_CTX-M-15 and bla_CTX-M-2.