Efficacy of rifampicin combination therapy on selected non-mycobacteria organisms isolated from a tertiary health institution in Benin city.

Abstract

Combination therapy or polytherapy is the use of more than one antibacterial agent in the treatment of a single infection. In this study, rifampicin that was mainly used in the treatment of mycobacterial infections has been used in combination with other agents in non mycobacterial organisms. Clinical isolates of Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa strains were exposed to antibacterial agents namely, Gentamicin, Cefuroxime, Ceftriaxone and Norfloxacin singly and also in combination with Rifampicin. Each minimum inhibitory concentration (MIC) as well as agar diffusion assays was determined. No antagonism was confirmed between rifampicin and any of the combination antibiotics evaluated. The study illustrated that synergy was most often observed with Staphylococcus aureus. The most potent combinations for Staphylococcus aureus were rifampicin and gentamicin, rifampicin and norfloxacin. However, Synergy was less often noted in the combination of 20μg rifampicin with Cefuroxime and ceftriaxone at varied concentration. At 10μg, there was no synergistic effect when compared with the use of Cefuroxime and ceftriaxone alone. At 20μg, Staphylococcus aureus and Escherichia coli were effectively inhibited, while at 30μg all isolates were inhibited. This study has also shown that MICs were lowest with norfloxacin, followed by cefuroxime, ceftriaxone than gentamicin. Moreso, cefuroxime, has minimal activity against Pseudomonas aeruginosa strain. However, the zones of inhibition of the drugs when the organisms were cultured in medium containing 20μg rifampicin had improved antibacterial outcomes as seen from the greater diameters of inhibition. Also, the results shows that the MIC of gentamicin monotherapy on Staphylococcus aureus gave 20ìg, but combination with rifampicin reduced the MIC to 10ìg, however the progeny of this test retained the MIC of the combined therapy (10ìg) on Staphylococcus aureus. Rifampicin combination therapy has enhance effect on some nonmycobacterial organisms; Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae and Pseudomonas aeruginosa compared to the single use of each drug.