Comparison of minimal inhibitory concentration and disk-diffusion antimicrobic sensitivity testing of bacterial pathogens isolated from food animals.

Disk-diffusion sensitivity tests were conducted with the antimicrobics sulfathiazole, gentamicin, erythromycin, kanamycin, penicillin, ampicillin, and spectinomycin on 300 to 350 bacterial isolates of food animal origin. The minimal inhibitory concentration of each antimicrobic was also determined for each bacterial isolate, using a microdilution technique. Results indicated that inhibitory zone sizes should be larger for some antimicrobics when testing animal pathogens than those zone sizes recommended for testing human pathogens. In addition, zone interpretive data are reported for spectinomycin, a drug for which such data were previously lacking.