Impact of treatment strategies on cephalosporin and tetracycline resistance gene quantities in the bovine fecal metagenome.
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The study objective was to determine the effects of two treatment regimens on quantities of ceftiofur and tetracycline resistance genes in feedlot cattle. The two regimens were ceftiofur crystalline-free acid (CCFA) administered to either one or all steers within a pen and subsequent feeding/not feeding of therapeutic doses of chlortetracycline. A 26-day randomized controlled field trial was conducted on 176 steers. Real-time PCR was used to quantify bla(CMY-2), bla(CTX-M), tet(A), tet(B), and 16S rRNA gene copies/gram of feces from community DNA. A significant increase in ceftiofur resistance and a decrease in tetracycline resistance elements were observed among the treatment groups in which all steers received CCFA treatment, expressed as gene copies/gram of feces. Subsequent chlortetracycline administration led to rapid expansion of both ceftiofur and tetracycline resistance gene copies/gram of feces. Our data suggest that chlortetracycline is contraindicated when attempting to avoid expansion of resistance to critically important third-generation cephalosporins.
Kanwar, N., Scott, H. M., Norby, B. o., Loneragan, G. H., Vinasco, J., Cottell, J. L., ... Boerlin, P.
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Kanwar, Neena||Scott, H Morgan||Norby, Bo||Loneragan, Guy H||Vinasco, Javier||Cottell, Jennifer L||Chalmers, Gabhan||Chengappa, Muckatira M||Bai, Jianfa||Boerlin, Patrick
