Synergistic Effect of Moxifloxacin and Imipenem against Acinetobacter Baumannii after Co-culture with a Resistant Shigella Flexneri

Abstract

Some microorganisms are capable of causing serious disease has become resistant to most commonly available antibiotics. Treating patients with drug-resistant pathogens have created a need for new therapies. In our study, we investigated the antimicrobial effect of combination antibiotics (clarithromycin, moxifloxacin, Imipenem) against Acinetobacter baumannii after co-culture with resistant Shigella flexneri. In our study, Kirby–Bauer disc diffusion antibiotic sensitivity testing was used which is essentially a qualitative or semi-quantitative test indicating the sensitivity or resistance of microorganisms to the test materials. Initially Acinetobacter baumannii was sensitive against the clarithromycin, imipenem and moxifloxacin in different concentration of 20, 40, 60 and 80 μg/ml. However, same concentrations of clarithromycin, imipenem and moxifloxacin showed no zone of inhibition against Shigella flexneri. After co-culture with two bacteria, both of them did not show optimum zone of inhibition against clarithromycin, imipenem and moxifloxacin at concentration of 20, 40, 60, and 80 μg/ml respectively. When high concentrations (120, 160, 180 μg/ml) of clarithromycin, Imipenem and moxifloxacin were used against the co-cultured pathogen, still no sensitivity was observed against the treated antibiotic. Our study shows that sensitive Acinetobacter baumannii become resistant after co-culture with resistant Shigella flexneri. Treatment with combination of Imipenem and moxifloxacin in different concentration of 20, 40, 60, and 80 μg/ml against newly resistant Acinetobacter baumannii showed sensitivity. Combination of Clarithromycin and imipenem with concentration of 20, 40, 60, and 80 μg/ml exhibited satisfactory zone of inhibition. Antibiotic combinations can be used as an alternative treatment approach in multi-drug resistant Shigella flexneri and Acinetobacter baumannii infections. The result of the combination antibiotic treatment also shows 10% greater effectiveness compared with single antibiotic against resistant pathogen which indicate synergistic effect of antibiotics.