Abstract
The use of antibiotics to treat dairy calves may result in multidrug-resistant extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli. This study investigated fluoroquinolone and macrolide resistance genes among ESBL-producing E. coli isolated from dairy calves. Fresh fecal samples from 147 dairy calves across three age groups were enriched to select for ESBL-producing E. coli. Plasmid-mediated fluoroquinolone (qnrB), macrolide (mph(A)), and beta-lactam (blaCTX-M groups 1 and 9) resistance genes were identified by PCR and gel electrophoresis in ESBL-producing E. coli. Beta-lactamase variants and antibiotic resistance genes were characterized for eight isolates by whole-genome sequencing. Seventy-one (48.3%) samples were positive for ESBL-producing E. coli, with 159 (70.4%) isolates identified as blaCTX-M variant group 1 and 67 (29.6%) isolates as blaCTX-M variant group 9. Resistance gene mph(A) was more commonly associated with blaCTX-M variant group 1, while resistance gene qnrB was more commonly associated with variant group 9. E. coli growth was quantified on antibiotic media for 30 samples: 10 from each age group. Significantly higher quantities of ceftriaxone-resistant E. coli were present in the youngest calves. Results indicate the dominant blaCTX-M groups present in ESBL-producing E. coli may be associated with additional qnrB or mph(A) resistance genes and ESBL-producing E. coli is found in higher abundance in younger calves.
Highlights
Introduction iationsAntibiotics are crucial for treating bacterial infections in humans and animals; drug-resistant pathogens can limit treatment options available
Determining potential selection factors for multidrug-resistant extendedspectrum beta-lactamase (ESBL)-producing E. coli in dairy calves and cattle will be valuable due to the highest-priority and critical importance of these antibiotics to human health and the potential for cross-over of antibiotic resistance into human pathogens and the environment
Resistance gene profiles for macrolide, fluoroquinolone, and cephalosporin antibiotics were identified by Polymerase chain reaction (PCR) for the blaCTX-M, qnrB, and mph(A) genes and revealed a significant relationship between the blaCTX-M variant group (1 or 9) and qnrB or mph(A) presence
Summary
Antibiotics are crucial for treating bacterial infections in humans and animals; drug-resistant pathogens can limit treatment options available. Many antibiotic classes remain critically important to human medicine, such as third-generation and higher cephalosporins, fluoroquinolones, and macrolides with drug resistance to any of these classes considered a serious threat to human health [1,2]. Antibiotic stewardship in food animal production has limited the use of antibiotics to U.S FDA-approved therapeutics with defined extralabel usage guidelines to reduce the risk of antibiotic resistance and potential cross-over into human pathogens; resistance remains common in food animals, posing a considerable public health concern [3,4,5]. Monitoring foodborne pathogens for existing and emerging antibiotic resistance profiles is essential to identifying potential public health threats.
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