EVALUATION OF THE POTENCY OF COMMERCIAL AND LOCALLY PREPARED ANTIBIOTIC DISCS ON CLINICAL BACTERIAL ISOLATES IN CALABAR, NIGERIA
Keywords:Antibiotic susceptibility testing, discs, potency.
Antibiotic susceptibility discs are used for vitro susceptibility testing of antimicrobial agents to fast growing bacteria and fastidious species by agar diffusion method. It is a semi quantitative method. This study was designed to assess the efficacy of commercial antibiotic discs over in-house prepared discs. Identified clinical isolates were obtained in house in the Department of Medical Microbiology/Parasitology, University of Calabar Teaching Hospital, Nigeria. Staphylococcus aureus (ATCC 7553) and Escherichia
Coli (ATCC 25922) were obtained and used as controls. The antibiotics tested includes: Ciprofloxacin, Erythromycin, Amoxicillin, Gentamicin, Zinacef. These were obtained commercially from Pharmacy shops. The local antibiotic discs were prepared with Whatman filter paper number 3. The antibiotic susceptibility testing was done using Kirby-Bauer method. Out of the 40 clinical isolates tested, 15(37.5%) were Staphylococcus aureus while 10(12.5%) each were Escherichia coli and Pseudomonas aeruginosa respectively. Only 5 isolates of Proteus vulgaris were used. The susceptibility profile of isolates to the commonly used local antibiotic discs ranged between 66.7% to 100%, while the range for commercial discs was 53.3% to 86.7%. Locally prepared discs were found to be more effective than commercial discs. The high resistance rates (0.0% to 33.3%) of clinical isolates to the commercial discs may be attributed to prolong exposure to environmental factors such as heat, moisture, sunlight as well as humidity when transported to retailers and the final users. There is need for constant monitoring and quality controls of susceptibility testing in our laboratories for the production of quality results and efficient patient care. Antibiotic susceptibility discs can be prepared locally for routine laboratory use; this may indirectly reduce importation of commercial discs and the burden on foreign exchange.