Microbiological and chemical detection of incurred penicillin G, oxytetracycline, enrofloxacin and ciprofloxacin residues in bovine and porcine tissues

Incurred penicillin G, oxytetracycline, enrofloxacin and ciprofloxacin resi dues in bovine and porcine muscle and kidney samples were analysed by micro biological and chemical methods, the former using Bacillus subtilis BGA as a test organism on agar media of pH 6, pH 7.2 and pH 8 and the latter using liquid chromatography. Least squares fits between the logarithms of the ch emically obtained concentrations of the antimicrobials and the widths of th e inhibition zones were used to estimate the inhibition zone widths corresp onding to the maximum residue limit concentrations. In vitro sensitivities were determined with standard antimicrobial solutions. The results indicate that if B. subtilis BGA is used as a test organism, muscle tissue cannot b e used as test material for screening oxytetracycline, enrofloxacin and cip rofloxacin residues on the plates used in this study, while penicillin G ca n be screened from muscle tissue. Because of the numerous factors causing o r increasing variation in the analysis, the inhibition zone caused by a giv en antibiotic concentration cannot be predicted precisely. Therefore, a pos itive agar diffusion test needs to be confirmed chemically. If a kidney sam ple gives a positive agar diffusion test result, the antimicrobial concentr ation in a muscle sample from the same carcass should be checked chemically .