In vitro effect of aminoglycosides and fluoroquinolones on staphylococcus aureus in the presence of folic acid

Abstract

Bacterial resistance in chemotherapy has been the bane of ocular disease management by health professionals. The desire to further probe and determine other possible causes of resistance gave rise to this study. A viable isolate of coagulase positive and pigment forming Staphylococcus aureus obtained from conjunctival swabs used in the study was treated with aminoglycosides (gentamicin, 0.3%, and tobramycin bramycin, 0.3%, ophthalmic solution) and fluoroquinolones (gatifloxacin 0.3% and moxifloxacin, 0.3% ophthalmic solution), in the presence and absence of folic acid (4.0% solution) respectively. The drug treated isolated culture of Staphylococcus aureus was incubated for 24 hrs at 370C. Results showed that in the presence of folic acid, gentamicin sensitivity was reduced by 19% while that of tobramycin was increased by 22%. On the other hand, there was a higher degree of reduction in sensitivity for the fluoroquinolones, gatifloxacin (34%) and maxifloxacin (20%) respectively. Inadvertent drug combination may be responsible for most antibiotic failures in therapy. The reduction in the efficacy of the antibiotics against the conjunctival isolate was found to be significant at p<0.05.

Key Words: aminoglycoside, fluoroquinolone efficacy resistance, staphylococcus aureus antagonism.