Antimicrobial resistance profiles of Escherichia coli and prevalence of
extended-spectrum beta-lactamase-producing Enterobacteriaceae in calves
from organic and conventional dairy farms in Switzerland
Abstract
This study compared the antimicrobial resistance (AMR) among commensal
Escherichia coli in the fecal microbiota of young calves raised on
organic and on conventional dairy farms in Switzerland. Further, fecal
carriage of extended-spectrum beta-lactamase (ESBL) producing
Enterobacteriaceae was assessed for calves from both farming systems.
Where possible, data on antimicrobial usage (AMU) were obtained.
Antimicrobial susceptibility testing was performed on a total of 71
isolates using the disk diffusion method. ESBL producers were
characterized by PCR-based multilocus sequence typing and sequencing of
the blaESBL genes. Organically raised calves were significantly more
likely to harbor E. coli that showed antimicrobial resistance to
ampicillin (OR 2.78, 95%CI 1.02–7.61, p=0.046), streptomycin (OR 3.22,
95%CI 1.17–8.92, p=0.046), kanamycin (OR 11.3, 95%CI 2.94–43.50,
p<0.001), and tetracycline (OR 3.25, 95%, 95%CI 1.13–9.31,
p=0.028). Calves with reported AMU were significantly more likely to
harbor E. coli with resistance to ampicillin (OR 3.91, 95%CI
1.03–14.85, p=0.045), streptomycin (OR 4.35, 95%CI 1.13–16.7,
p=0.045), and kanamycin (OR 8.69 95%CI 2.01–37.7, p=0.004).
ESBL-producing Enterobacteriaceae (18 E. coli and 3 Citrobacter braakii)
were detected exclusively among samples from conventionally farmed
calves (OR infinity (∞), 95%CI 2.3–∞, p< 0.0013). The
observations from this study suggest that AMR is highly prevalent among
commensal E. coli in young dairy calves, irrespective of the farm
management system, with proportions of certain resistance phenotypes
higher among organic calves. By contrast, the occurrence of ESBL
producers among young dairy calves may be linked to factors associated
with conventional farming.