Use of Alternative Indicator Organisms for The Microbiological Assay of Four Antibiotics Commonly Sold in Uyo, Nigeria

Background: The accurate measurement of antibiotics potency is essential for quality checks, and microbiological assays have been used extensively for this purpose. Unfortunately, in most places especially in the developing countries, the indicator organisms recommended for these assays are difficult to obtain as there are no culture collection centers that keep them. Alternative indicator organisms which will meet the specifications of the reference books were therefore sought for and used in the microbiological assay of some commonly used antibiotics. Pure powders of four commonly used antibiotics to be assayed were obtained and confirmed using the Fourier infrared spectroscopy. Nine strains of organisms which are Escherichia coli WG5, Enterococcus duranss ATCC 11576 and Staphylococcus aureus NCTC6571, Pseudomonas aersuginosa ATCC 27853, Enterococcus gallinarium ATCC 49573, Enterococcus faecium ATCC 49185, Stenotrophomonas maltophilia ATCC 13637, Aeromonas hydrophilia ATCC 7966 and Listeria monocytogenes were randomly selected and screened for their suitability to be used based on their susceptibility to the antibiotics to be assayed, growth characteristics, linearity on a dose response curve and pathogenicity. Selected organisms were eventually used as indicator organisms in the microbiological assay of different brands of Ampicillin, Amoxicillin, Tetracycline and Erythromycin obtained in Uyo, Nigeria using the 6x6(3+3) Latin square design on assay plates. Results: Results obtained confirmed the standard antibiotic powders and showed that Staphylococcus aureus NCTC6571 could be used to assay Amoxicillin while Enterococcus durans ATCC 11576 and Escherichia coli WG5 could be used to assay Erythromycin, Ampicillin. and Tetracycline Results further showed that the antibiotics assayed had percentage potency of between 104 and168%. All assayed products were within acceptable limits confirming all the antibiotics assayed to be of good quality, except the amoxicillin capsule which exceeded the percentage potency limit allowed. Conclusion: It is concluded that alternative indicator organisms that meet the specifications of reference books can be used for the microbiological assay of antibiotics in the absence of those recommended.