Evidence for Transfer of CMY-2 AmpC β-Lactamase Plasmids between Escherichia coli and Salmonella Isolates from Food Animals and Humans

Abstract

Escherichia coli is an important pathogen that shows increasing antimicrobial resistance in isolates from both animals and humans. Our laboratory recently described Salmonella isolates from food animals and humans that expressed an identical plasmid-mediated, AmpC-like ␤-lactamase, CMY-2. In the present study, 59 of 377 E. coli isolates from cattle and swine (15.6%) and 6 of 1,017 (0.6%) isolates of human E. coli from the same geographic region were resistant to both cephamycins and extended-spectrum cephalosporins. An ampC gene could be amplified with CMY-2 primers in 94.8% of animal and 33% of human isolates. Molecular epidemiological studies of chromosomal DNA revealed little clonal relatedness among the animal and human E. coli isolates harboring the CMY-2 gene. The ampC genes from 10 animal and human E. coli isolates were sequenced, and all carried an identical CMY-2 gene. Additionally, all were able to transfer a plasmid containing the CMY-2 gene to a laboratory strain of E. coli. CMY-2 plasmids demonstrated two different plasmid patterns that each showed strong similarities to previously described Salmonella CMY-2 plasmids. Additionally, Southern blot analyses using a CMY-2 probe demonstrated conserved fragments among many of the CMY-2 plasmids identified in Salmonella and E. coli isolates from food animals and humans. These data demonstrate that common plasmids have been transferred between animal-associated Salmonella and E. coli, and identical CMY-2 genes carried by similar plasmids have been identified in humans, suggesting that the CMY-2 plasmid has undergone transfer between different bacterial species and may have been transmitted between food animals and humans.

Effect of cefovecin on the fecal flora of healthy dogs

“…Acquisition of this gene may explain the cross resistance seen among β-lactams in this study. Furthermore, co-residence of multiple resistance genes has been documented in E. coli carrying the bla CMY-2 gene, which may help to explain the resistance seen in the fecal E. coli of the present study to doxycycline, enrofloxacin, gentamicin, and imipenem (Winokur et al, 2001). …”

Antibiotic Resistance and the Prospects of Medicinal Plants in the Treatment of Salmonellosis

“…typhimurium strains carrying indistinguishable CMY-2-encoding plasmids were isolated in Nebraska from a patient and cattle during a local outbreak of salmonellosis, demonstrating that the Salmonella-resistant strain evolved primarily in livestock . Since 1998, Salmonella of human and animal origin were reported to show resistance to expanded-spectrum cephalosporins, in Iowa (Winokur et al, 2000;Winokur et al, 2001). Molecular studies demonstrate the emergence of plasmid encoded CMY-2 β-lactamase in most cephalosporin resistant isolates.…”

“…Molecular studies demonstrate the emergence of plasmid encoded CMY-2 β-lactamase in most cephalosporin resistant isolates. During the 1998-1999 periods, nearly 16% of E. coli isolates and 5.1% of Salmonella isolates from clinically ill animals in Iowa produced CMY-2 (Winokur et al, 2000;Winokur et al, 2001). Similar plasmids, carrying the cmy-2 gene were also reported in Salmonella isolated from animals in Illinois (Odeh et al, 2002).…”

Antibiotic Resistance in Salmonella: A Risk for Tropical Aquaculture

“…In one study, salmonelas isolated from food animals were found to carry CMY-2, a plasmidmediated AmpC-like β-lactamase (Winokur et al, 2001). Doublet et al (2004) found florR (a florfenicol resistance gene) and bla CMY-2 plasmids to be responsible for resistance to widespectrum cephalosporines in salmonelas isolated from clinical samples, animals and foods in the US.…”