Abstract

The outcome of in vitro interaction of standard antibiotics with ethanolic leaf extracts of three medicinal plants (Picralima nitida, Chromolaena odorata andAspilia africana) against antibiotic resistant bacteria was investigated by agar disc diffusion methods and macrobroth dilution techniques. At least three isolates each of Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa that were resistant to more than two of the following antibiotic discs were used: erythromycin, chloramphenicol, tetracycline, norfloxacin and ciprofloxacin. A subinhibitory concentration (1/4th MIC) of the plant extracts were combined with the antibiotics against the resistant bacteria isolates using both antibiotic disc diffusion technique and macrobroth dilution test. The extract of A. africana enhanced 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. It also enhanced the activities of tetracycline and norfloxacin against antibiotic resistant S. aureus. The extract of C. odorata greatly 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 levels of antagonism with ciprofloxacin and norfloxacin against almost all the test bacteria. These results 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. nitida could be therapeutically wasteful. Their use in combination with conventional antibiotics should be further studied for in vivo activities. This may lead to the development of much needed drug enhancing preparations.

Key words: Medicinal plants, antibiotics, antibiotic-extract combination, multidrug-resistant bacteria.