Evaluation of Antibacterial and Resistance Modifying Potency of Ethanolic Leaf Extracts of Four Medicinal Plants.

Abstract

In vitro antibacterial and resistance modulatory potency of ethanolic leaf extracts of four medicinal plants (Picralimanitida, Chromolaenaodorata, Aspiliaafricanaand Hyptissuaveolens) were evaluated using agar well diffusion and macrobroth dilution techniques. Four isolates of each of the following bacteria were treated with the plant extracts: Pseudomonas aeruginosa, Escherichia coli, Salmonella spp., Staphylococcus aureusand Bacillus cereus. The minimum inhibitory concentration (MIC) values of the extracts varied from 1.56 mg/ml to 31.25 mg/ml in macrobroth dilution test. The extracts exhibited the best activity at extract concentration of 100 mg/ml in the agar well diffusion test with average inhibition zone diameters that ranged from 11 mm to 22 mm. The extract of H. suaveolenshad the least activity against all the test organisms, while the extract of P. nitida was the most active extract against E.coli and Salmonella. The extracts of C.odorata and A. africanawere the most active against S. aureus and P. aeruginosa (P<0.05). A number of isolates of E. coli, P. aeruginosa and S. aureuswere tested for their resistance or sensitivity to the following antibiotic discs: ciprofloxacin, norfloxacin, tetracycline, chloramphenicol and erythromycin. The antibiotic resistant isolates were then selected and used in the resistance modulatory assay.Asubinhibitory concentration (1/4th MIC) of the plant extracts were combined with the antibiotics against the resistant bacterial isolates using both antibiotic disc diffusion technique and macrobroth dilution test. The extract of A. africanaenhanced the activities of the test antibiotics (except erythromycin) against resistant E. coli, and also enhanced the activities of ciprofloxacin, norfloxacin and chloramphenicol against antibiotic resistant P. aeruginosa, but only enhanced the activities of tetracycline and norfloxacin against antibiotic resistant S. aureus. The extract of C. odoratagreatly enhanced the activities of the antibiotics (except erythromycin) against the resistant P. aeruginosa and also potentiated the activities of chloramphenicol and tetracycline against resistant S. aureus. Although the extract of P nitida potentiated few antibiotics such as tetracycline and chloramphenicol against resistant E. coli, the extract exhibited high level of antagonism with ciprofloxacin and norfloxacin against almost all the test bacteria. The extract of H. suaveolensdid not have any effect on the activities of the antibiotics. These results provide justification for traditional use of leaf extracts of these medicinal plants for treatment of various infections. The results also suggest that extracts of C. odorata and A. africana could be good sources of multidrug resistance inhibitors, and indicate that indiscriminate co-administration of antibiotics with some herbal drugs such as those from P. nitidacould be therapeutically wasteful.