Abstract:
The uncontrolled and unrestricted use of antimicrobials may lead to undesirable drug residues in the treated animals and their products. However, in the Kenyan poultry industry there is lack of affordable, easy to perform antibiotic residues screening methods. The aim of this study was to evaluate the performance of Bacillus subtilis as test organism for assay of beta-lactam antibiotics in chicken meat. Microbiological detection was achieved by agar well diffusion. The test bacteria grew optimally at a pH range of 6-7.3. Zone diameters decreased significantly (p<0.001) when B. subtilis was used to detect penicillin G (PEN G) at decreasing pH from 7.3, 7.0 to 6. There was
significant (p<0.001) difference in the detection of PEN G in both kidney and liver samples at the different pH values although high antibiotic concentrations produced zones that were not significantly different. It was concluded that the pH of the growth media influences the growth of test organism. Although PEN G was reliably detected below the MRLs, of 50ng/g in both liver and kidney by B. subtilis, the pH of the growth media and type of organ affected both the detection and the limits of detection (LODs) of this antibiotic. Bacillus subtilis plate at pH 7.3 can be used effectively for routine screening for residues of PEN G in chicken kidney and liver tissues. The B. subtilis plate had LOD of 0.1ng/ml in both liver and kidney tissues. This screening test is technically simple and can be carried out in any laboratory.
