A microbiological six-plate method for the identification of certain antibiotic groups in incurred kidney and muscle samples

A microbiological method was developed for group level identification of an tibiotics in incurred kidney and muscle samples from cattle and pigs. The m ethod was composed of six test bacterium-plate growth medium combinations a nd the result was recorded as a profile of growth inhibition zones. The sam ple profiles were compared to two sets of references: one constructed with standard antibiotic solution profiles, and the other with these combined wi th profiles of microbiologically and chemically identified residues from in curred samples. The algorithm employed in profile comparison located the mi nimal sum of absolute pairwise differences over the tests, with the additio n of a number of experimentally observed intra-test criteria. Chemical iden tification and quantitation of incurred residues was based on liquid chroma tography. The method identified penicillin G as a penicillinase sensitive p enicillin, enrofloxacin and ciprofloxacin belonging to fluoroquinolone grou p, and oxytetracycline belonging to tetracycline group. Each of these resid ues was microbiologically identified below the Maximum Residue Limit (MRL) for kidney tissue. Combining sample profiles with the standard reference da ta set did not enhance the resolution. Microbiological and chemical identif ication test results were in good agreement. The results of this study show that a microbiological identification method is a useful tool in prelimina ry characterisation of antibiotic residues in animal tissues.