In-vitro assessment of antibacterial effects of combined crude extracts of S. glaucescens and C. swynnertonii with antibiotics

Currently, there is an upsurge of bacterial resistance in single-drug treatment regimens. This has stimulated a growing interest in research and development of new antibacterial agents containing several ingredients as one of the means to combat bacterial resistance. Herb-antibiotic combination therapy is one of the reported effective treatment regimens to combat antimicrobial resistance. This study was aimed to assess antibacterial effects of combined crude extracts of Synadenium glaucescens and Commiphora swynnertonii with antibiotics. In this study, three standard antibiotic drugs namely, ciprofloxacin, ampicillin and erythromycin in combination with crude extracts from S. glaucescens and C. swynnertonii were screened for antibacterial effects against two Gram-positive bacteria, Staphylococcus aureus and Enterococcus faecalis and three Gram-negative bacteria Escherichia coli, Klebsiella pneumonia and Pseudomonas aeruginosa. Broth microdilution technique was used to determine the Minimum Inhibitory Concentration (MIC) while Fractional Inhibitory Concentration (FIC) indices were calculated from MIC values of combined extracts to determine the combination effects. Synergism was observed when ciprofloxacin was combined with all tested crude extracts against E. coli (ΣFIC of 0.02), combination of ciprofloxacin with extract from root barks of C. swynnertonii (ΣFIC of 0.5) against S. aureus, root barks of Synadenium glaucescens (ΣFIC of 0.1) against S. aureus and combination of ampicillin with all tested crude extracts (ΣFIC of 0.03-0.1) against E. faecalis. Moreover, antagonism was observed between the combinations of ampicillin and erythromycin with all tested crude extracts against Gram-negative bacteria (ΣFIC of 4-8). Therefore, the combinations which demonstrated synergism may be promising alternatives for the treatment of infectious diseases caused by E. coli, S. aureus and E. faecalis. However, in the future, toxicity studies for combinations which demonstrated synergism are recommended. Key words: Antibacterial activity, antibiotic, crude extracts, herbs, synergism.