BACTERIA RESISTANT TO ANTIMICROBIALS CRITICALLY IMPORTANT TO HUMAN MEDICINE IN BEEF CATTLE PRODUCTION AND PROCESSING ENVIRONMENTS

摘要

Concerns have been raised that therapeutic use of ceftiofur in cattle at feedlots may increase the prevalence of third generation cephalosporin-resistant (3GC~r) Escherichia coli. However, fecal and hide 3GC~r E. coli prevalences throughout a longitudinal study of cattle at a feedlot, including during the period of greatest ceftiofur use at the feedlot, were either not significantly different or significantly less than the respective prevalences at arrival. In the United States the DlacMYgene is frequently identified in 3GC~r E. coli and 3GC~r Salmonella from both human and cattle sources. Molecular characterization of 3GC~r E. coli isolates indicated that clonal expansion of feedlot-adapted blacmE. coli strains contributed more to the persistence of blacMY than horizontal transfer of bacMY between E. coli strains at this feedlot. These results demonstrate that therapeutic use of ceftiofur at this cattle feedlot did not significantly increase the herd prevalence of 3GC~r E. coli. Specific concernshave also been raised that 3GCr E. coli, trimethoprim-sulfamethoxazole-resistant (COT~r) E. coli, 3GC~r Salmonella, and nalidixic acid-resistant (NAL~r) Salmonella that may be present in cattle production environments, persist through beef processing, and contaminate final products. The prevalences and concentrations of these organisms were determined in feces and hides (at feedlot and processing plant), pre-evisceration carcasses, and final carcasses from three lots of fed cattle.