Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the major causes of nosocomial and community infections. It has shown resistance to most of the currently available antibiotics and nicknamed ‘super bug’. Anti-staphylococcal activities of tannic acid, quercetin and gallic acid ethyl ester in combination with fusidic acid and rifampicin were determined against five strains of S. aureus, including three clinical strains. Tannic acid and quercetin were found to be synergistic with fusidic acid and rifampicin. The effects of these combinatory pairs on the adaptive resistance of S. aureus were also studied. The strains were studied for ten incubation cycles under continuous influence of fusidic acid/rifampicin alone and in combination with fixed dose of phytochemicals. The minimum inhibitory concentrations (MIC) of the exposed strains were determined after every cycle to study their resistance to the antibiotic. Based on the results at the end of the tenth cycle, the fusidic acid/rifampicin exposed strains gradually selected for resistance at higher MIC values. On the other hand, the combination exposed strains demonstrated stable MIC values for the antibiotics. The results suggested prevention or delay of fusidic acid and rifampicin resistance by adding synergistic phytochemicals.

Key words: Staphylococcus aureus, antibiotic resistance, antibiotic combination, phytochemicals, MRSA.

Abbreviation

Abbreviations: MRSA, Methicillin-resistant Staphylococcus aureus; MIC, minimum inhibitory concentrations; CLSI, clinical and laboratory standards institute; MSSA,methicillin sensitive Staphylococcus aureus; NUH, national university hospital; IS, iso-sensitest; FIC and FICI, fractional inhibitory concentration and index; CFU, colony forming units; DNA, deoxyribonucleic acid; PAP, population analysis profile.