Browsing by Author "Mirzaagha, Parasto"
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- ItemOpen AccessCharacterization of antibiotic resistance in ampicillin and tetracycline resistant escherichia coli from feedlot cattle fed subtherapeutic antimicrobials(2008) Mirzaagha, Parasto; McAllister, Tim; Louie, MarieThe study investigated tetracycline- and ampicillin-resistant Escherichia coli selected from feces of calves that were or were not administered in-feed subtherapeutic antimicrobials. Antimicrobial resistance (AMR) persisted throughout the experiment even in the absence of in-feed antibiotics. Transmission of E. coli isolates among cattle was evident, particularly among animals within a single pen. In addition, shedding of E. coli biotypes was observed to occur transiently throughout the feeding period. Administration of subtherapeutic levels of antimicrobials did not have a major impact on AMR E. coli as compared to control steers, except for the observation that administration of chlortetracycline and sulfamethazine increased the number of ampicillin-resistant isolates that also exhibited resistance to sulfamethoxazole and chloramphenicol. Molecular characterization of isolates found tet(B) to be the most prevalent determinant among the tetracycline-resistant isolates and teml-like determinant to be most prevalent among the ampicillin-resistant isolates. Results suggest that AMR inĀ£. coli is complex and is likely affected not only by the administration of antibiotics but also by numerous other presently undefined environmental and management factors.