A SIX PLATE MICROBIOLOGICAL ASSAY FOR SCREENING OF ANTIMICROBIAL RESIDUES IN FOOD OF ANIMAL ORIGIN

Occurrence of antimicrobial residues in livestock and aquatic products is a current public health concern. The monitoring of food commodities for antimicrobial residues will ensure the consumer safety and promote trade. Therefore, the objective of this study was to establish a screening test to detect antimicrobial residues in food of animal origin. A bioassay consists of six plates was established, which enables screening of six groups of antimicrobials, namely; penicillins, sulphonamides, streptomycin, erythromycin, tetracyclines and fluroquinolones. The Six Plate Test (SPT) is a bioassay technique, which is carried out using Bacillus subtilis BGA (Merck), Bacillus cereus (ATCC 11778), Micrococcus luteus (ATCC 9341) and Escherichia coli (ATCC 11303) as indicator organisms. The Mueller Hinton Agar (MHA) was used as the test medium at optimum pH for all indicator organisms except B.cereus, for which the Media No.8 was used. The Minimum Detectable Concentrations (MDC) of SPT were determined using serial dilutions of antibiotics. All the MDC values obtained on SPT for the validated antimicrobials were below the recommended MRL of each antimicrobial. SPT can be developed to a quick, easy to perform, robust and low cost screening test to detect antimicrobial residues in food of animal origin.