Investigation of antibacterial effects of herb-herb and herb-antibiotic combinations

Abstract

Introduction Several studies have reported the failure of single-drug treatment regimens for bacterial infections due to emergence of bacterial resistance. Hence, there has been a growing interest in researching and developing new antibacterial drugs, containing several combined ingredients as one of the means to combat bacterial resistance. Among the successful reported antibacterial combination treatments include herb-herb and herb-antibiotic. This study investigated the antibacterial effects of single and combined extracts from leaves, stems and root barks of Commiphora swynnertonii and Synadenium glaucescens. In addition, the study evaluated antibacterial effects of combined crude extracts of two medicinal plants, also the extracts were combined with selected three antibiotics namely ciprofloxacin, ampicillin, and erythromycin. Methods C. swynnertonii and S. glaucescens were respectively collected from Manyara and Njombe regions of Tanzania. The standard antibiotics used as positive control in this study were gentamicin, ciprofloxacin, ampicillin, and erythromycin. Extraction of plant materials was done by soxhlet and macerations methods using dichloromethane and methanol solvents respectively. The extracts were assessed for their effects on Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis) and Gram- negative bacteria (Escherichia coli, Klebsiella pneumonia, and Pseudomonas aeruginosa). Minimum Inhibitory Concentrations (MIC) was determined by broth micro dilution method while Fractional inhibitory concentration (FIC) indices were calculated from MIC values of individual and combined crude extracts to determine combination effects. Findings Strong antibacterial activities were demonstrated by all extracts of S. glaucescens (MIC 0.01-0.37mg/mL) and methanol extracts of C. swynnertonii (MIC 0.04-0.37mg/mL) against Gram-positive bacteria Synergistic effect was observed in combination of methanol extracts of C. swynnertonii stem barks and S. glaucescens leaves against S.aureus (∑FIC 0.5), other synergistic effects were observed against E. faecalis in combination of dichloromethane extracts of C. swynnertonii stem barks and S. glaucescens stem barks (∑FIC 0.5), and C. swynnertonii root barks and S. glaucescens root barks (FIC index 0.3). For the remaining combinations of crude extracts, mainly additive effects were observed. The combinations of crude extracts with antibiotics revealed synergism 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 S. 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. Nevertheless, antagonism was observed between the combinations of ampicillin and erythromycin with all tested crude extracts against Gram- negative bacteria (ΣFIC of 4-8). Conclusions When two or more plant parts are combined among themselves or with antibiotics, the resulting antibacterial effects may either be synergistic, additive or antagonistic depending on the phytochemical contribution of each plant or part and also the bacteria or diseases intended. Recommendations Synergistic effects demonstrated in this study provide promising good combinations to be considered as alternative antimicrobials. Toxicity studies of the combinations of S. glaucescens stem barks of and C. swynnertonii leaves and S. glaucescens root barks and C. swynnertonii root barks which showed synergistic effects against Gram-positive bacteria are recommended in the future.