In vitro Combination Studies of Antibiotics against Bacterial Pathogens

Abstract

Antibiotic-resistant microorganisms are emerging worldwide and causing serious complications. As these microorganisms are resistant to most of the contemporary antibiotics, their control is becoming as a global health concern. Therefore, there is a need for new alternative compounds or strategies that are effective against these microbial infections and in preventing or delaying their resistance. This study was carried out to test Rifampicin as an adjuvant therapeutic agent in the treatment of infections caused by Gram-positive as well as negative Bacteria. For this purpose, two antibiotics — Doxycycline and Ciprofloxacin — were studied in combination with Rifampicin. Fractional inhibitory concentration index showed synergistic effect when Rifampicin is used in combination with Doxycycline and the effect was found to be additive in nature when used in combination with ciprofloxacin. Hence, Rifampicin in combination with Doxycycline is considered to be better than the combination of Rifampicin and Ciprofloxacin. This is also confirmed by mutation prevention concentration results where Rifampicin had Mutation Prevention Concentration (MPC) greater than 256 µg/ml against all the pathogens included in study but when Rifampicin was used in combination with 1 µg/ml Doxycycline, the concentration of Rifampicin was reduced to 16 µg/ml while in combination with Ciprofloxacin, its concentration was 32 µg/ml against S. aureus ATCC 29213. The synergistic combinatory effect of the given antibiotics was studied only for S. aureus to understand the dynamic drug combination response. S. aureus is one of the major causes of nosocomial and community infections. It has shown resistance to most of the currently available antibiotics.