02646naa a2200301 a 450000100080000000500110000800800410001902400300006010000150009024501430010526000090024850001030025752016450036065300290200565300220203465300270205665300170208365300310210070000170213170000150214870000170216370000200218070000180220070000170221870000150223570000180225077300760226810575652018-09-13       2017    bl uuuu     u00u1 u    #d7 a10.1128/AEM.01682-172DOI1 aVIKRAM, A.  aImpact of "Raised Without Antibiotics" beef cattle production practices on occurrences of antimicrobial resistance.h[electronic resource]  c2017  aArticle  history: Accepted manuscript posted online 8 September 2017// published in november 2017.  aThe specific antimicrobial resistance (AMR) decreases that can be expected from reducing antimicrobial (AM) use in United States (US) beef production have not been defined. To address this data gap, feces were recovered from 36 lots of ?raised without antibiotics? (RWA) and 36 lots of ?conventional? (CONV) beef cattle. Samples (N = 719) were collected during harvest and distributed over a year. AMR was assessed by: i) culture of six AM-resistant bacteria (ARB); ii) qPCR for 10 AMR genes (ARGs); iii) an qPCR array of 84 ARGs; and iv) metagenomic sequencing. Generally, AMR levels were similar, but some were higher in CONV. The prevalence of third-generation cephalosporin-resistant (3GCr) Escherichia coli was marginally different between production systems (47.5 % CONV, 34.8% RWA, P = 0.04), but the seasonal effect (92.8% summer, 48.3% winter, P < 0.01) was greater. Erythromycin-resistant (ERYr) Enterococcus spp. concentrations significantly differed between production systems (CONV = 1.91 log10 CFU/g, RWA = 0.73 log10 CFU/g, P < 0.01). Levels of aadA1, ant(6)-I, blaACI, erm(A), erm(B), erm(C), erm(F), erm(Q), tet(A), tet(B), tet(M), and tet(X) ARGs were higher (P < 0.05) in CONV. Aggregate abundances of all 43 ARGs detected by metagenomic sequencing and the aggregate abundances of ARGs in the aminoglycoside, ?-lactam, macrolide-lincosamide-streptogramin B (MLSB), and tetracycline AM classes did not differ (log2 fold change < 1.0) between CONV and RWA. These results suggest that further reductions of AM use in US beef cattle production may not yield significant AMR reductions beyond MLSB and tetracycline resistance.  aANTIMICROBIAL RESISTANCE  aBACTERIAL CULTURE  aBEEF CATTLE PRODUCTION  aMETAGENOMICS  aRAISED WITHOUT ANTIBIOTICS1 aROVIRA, P.J.1 aAGGA, G.E.1 aARTHUR, T.M.1 aBOSILEVAC, J.M.1 aWHEELER, T.L.1 aMORLEY, P.S.1 aBELK, K.E.1 aSCHMIDT, J.W.  tApplied and Environmental Microbiology, 2017gv. 83, no. 22, e01682-17.