The
antibiotics apramycin and
carbadox were fed to growing swine, and the prevalence of Salmonella isolates that are resistant to
apramycin and related
aminoglycoside antibiotics was examined. Three hundred twelve Salmonella-positive pigs raised on one of five farms in an integrated swine operation and slaughtered at a central plant were used. All farms fed
carbadox during the grower phase, and two farms administered
apramycin during the first 21 days of age. Ileocolic lymph nodes and cecal contents were sampled at slaughter. One hundred of the 312 pigs were randomly selected to examine
apramycin- and
carbadox-resistant
Salmonella infection, while all 312 pigs were used to evaluate the association between
apramycin exposure and
infection with Salmonella organisms resistant to
amikacin,
gentamicin,
kanamycin, and
streptomycin. Antimicrobial resistance was determined using disk diffusion and breakpoint concentrations.
Apramycin treatment appeared to have little effect on
apramycin- (12.5 versus 20.9%) or
streptomycin- (76.4 versus 73.5%) resistant Salmonella isolates when averaged across farms and compared to control animals. Feeding
carbadox resulted in
carbadox-resistant
Salmonella infection in only 5.3% of the isolates on one farm. The prevalence of
amikacin-,
gentamicin-, and
kanamycin-resistant Salmonella isolates on farms feeding
apramycin and
carbadox were 0, 0, and 1.8%, respectively. Serogroup B was the most prevalent serogroup isolated, followed by C1 and E1.
Apramycin and
carbadox treatment did not appear to have any effect on the serogroup isolated. Subtherapeutic use of
carbadox and
apramycin did not appear to increase the prevalence of antimicrobial-resistant Salmonella in market-age swine.