Determination of penicillin G, ampicillin, and cephapirin residues in tissues.

A cylinder plate microbiological method was developed for the rapid, quantitative determination of penicillin G, ampicillin, and cephapirin in animal tissues. The method uses agar plates seeded with stable spores of Bacillus stearothermophilus var. calidolactis and incubated 4 h at 64 degrees C. Standard curves were obtained for the following ranges of concentration of antibiotics in tissues: 0.02-0.32 IU penicillin G/g, 0.0125-0.2 micrograms ampicillin/g, and 0.02-0.32 micrograms cephapirin/g. The proposed method is suitable not only for penicillin residue analysis, for which the sensitivity has been greatly improved compared with the Sarcina lutea method, but also for depletion studies on these antibiotics, which are commonly used to treat diseases in food-producing animals.