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United States Department of Agriculture

Agricultural Research Service

Research Project: IMPROVING THE EFFICIENCY AND SUSTAINABILITY OF DIVERSIFIED FORAGE-BASED LIVESTOCK PRODUCTION SYSTEMS

Location: Forage and Livestock Production Unit

Title: Evaluation of antimicrobial resistance of bovine bacteria to antibiotics

Authors
item Tiller, Glennda -
item Gothard, Cord -
item Appeddu, Lisa -
item Brown, Mike -
item Von Tungeln, David

Submitted to: Journal of Global Antimicrobial Resistance
Publication Type: Abstract Only
Publication Acceptance Date: April 15, 2013
Publication Date: N/A

Technical Abstract: Antimicrobial resistance (AMR) is one of the most formidable threats to human medicine today. Therefore, the research objective is to evaluate the susceptibility of Staphylococcus species isolated from beef cows to 12 antibiotics commonly used in treating human and animal infections. This research was done in collaboration with USDA-ARS Grazinglands Research Laboratory as part of another study evaluating the prevalence of mastitis in beef cows. Bacteria had been previously harvested from milk samples aseptically collected in 2011; only Staphylococcus aureus and Coagulase Negative Staphylococcus (CNS) were evaluated for AMR (n = 64). Antibiotics tested were Penicillin, Ampicillin, Gentamicin, Tetracycline, Erythromycin, Trimethoprim-sulfamethoxazole, Pirlimycin, Enrofloxacin, Cephalothin, and Ceftiofur; Oxacillin and Cefoxitin were used to evaluate AMR to Methicillin. Procedures of the Clinical Laboratory Standards Institute were followed to test for AMR via the disk diffusion assay on Mueller-Hinton Agar. Tests were run in duplicate for each microbe, and the resulting antimicrobial disk susceptibility zone of inhibition diameters were recorded. S. aureus ATCC 25923 was used as a reference strain to ensure acceptable test conditions. One microbe was omitted from testing, as it never grew in an amount sufficient to obtain reliable measures. None of the remaining 63 bacteria exhibited resistance to any of the 12 antibiotics tested. However, an intermediate resistance to Erythromycin was detected in 22 bacteria; these tests will be repeated and reported. Results indicate a low level of AMR in bacteria isolated from beef cows, suggesting the use of antibiotics in Agriculture may not be a significant contributor to the emerging AMR challenge in human health.

Last Modified: 10/22/2014
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