03064naa a2200361 a 450000100080000000500110000800800410001902200140006002400300007410000190010424501070012326000090023030001260023950001320036552018450049765000120234265300260235465300250238065300110240565300170241665300260243370000160245970000140247570000200248970000160250970000170252570000150254270000130255770000180257070000170258870000150260577300820262010588282018-11-28       2018    bl uuuu     u00u1 u    #d  a0099-22407 a10.1128/AEM.00610-182DOI1 aWEINROTH, M.D.  aEffects of ceftiofur and chlortetracycline on the resistomes of feedlot cattle.h[electronic resource]  c2018  cThis is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license.  aArticle history: Received 15 March 2018. / Accepted 24 April 2018. / Accepted manuscript posted online 4 May 2018. OPEN ACCESS.  aABSTRACT. Treatment of food-producing animals with antimicrobial drugs (AMD) is controversial because of concerns regarding promotion of antimicrobial resistance (AMR). To investigate this concern, resistance genes in metagenomic bovine fecal samples during a clinical trial were analyzed to assess the impacts of treatment on beef feedlot cattle resistomes. Four groups of cattle were exposed, using a 2-by-2 factorial design, to different regimens of antimicrobial treatment. Injections of ceftiofur crystalline- free acid (a third-generation cephalosporin) were used to treat all cattle in treatment pens or only a single animal, and either chlortetracycline was included in the feed of all cattle in a pen or the feed was untreated. On days 0 and 26, respectively, pre- and posttrial fecal samples were collected, and resistance genes were characterized using shotgun metagenomics. Treatment with ceftiofur was not associated with changes to ?-lactam resistance genes. However, cattle fed chlortetracycline had a significant increase in relative abundance of tetracycline resistance genes. There was also an increase of an AMR class not administered during the study, which is a possible indicator of coselection of resistance genes. Samples analyzed in this study had previously been evaluated by culture characterization (Escherichia coli and Salmonella) and quantitative PCR (qPCR) of metagenomic fecal DNA, which allowed comparison of results with this study. In the majority of samples, genes that were selectively enriched through culture and qPCR were not identified through shotgun metagenomic sequencing in this study, suggesting that changes previously documented did not reflect changes affecting the majority of bacterial genetic elements found in the predominant fecal resistome.  © 2018 American Society for Microbiology.  aFEEDLOT  aANTIBIOTIC RESISTANCE  aANTIMICROBIAL AGENTS  aCATTLE  aMETAGENOMICS  aPOSTANTIBIOTIC EFFECT1 aSCOTT, H.M.1 aNORBY, B.1 aLONERAGAN, G.H.1 aNOYES, N.R.1 aROVIRA, P.J.1 aDOSTER, E.1 aYANG, X.1 aWOERNER, D.R.1 aMORLEY, P.S.1 aBELK, K.E.  tApplied and Environmental Microbiology, July 2018, vol. 84, no.13, e00610-18.