Abstract

Microorganisms are becoming resistant to almost all existing and newly discovered antimicrobial agents. This has led to ineffective treatment of infectious diseases with increased risk of complications. Few medicinal plants have been found to exhibit the ability of reversing the resistance mechanisms of microbes to antibiotics. The study investigates the influence of leaf methanol extracts of Hilleria latifolia and Laportea ovalifolia on some commonly used antibiotics.  Micro-dilution technique was used to determine the antimicrobial activity and minimum inhibitory concentration (MIC) of the leaf extracts and the selected antibiotics. MICs of the antibiotics in presence of sub-inhibitory concentration of the extracts were determined.  MIC of H. latifolia and L. ovalifolia extracts ranged from 50 to 100 mg/ml. In the presence of sub-inhibitory concentration (5 mg/ml) of the extracts, the activity of the antibiotics was modified with enhanced or reduced activity. The activity of amoxicillin was potentiated by 8-folds, 4-folds, 2-folds, 8-folds, and 2-folds against Escherichia coli, Bacillus subtilis, Salmonella typhi, Staphylococcus aureus and Pseudomonas aeruginosa, respectively in the presence of leaf extract of H. latifolia. Activity of ampicillin was potentiated by 2- and 4-folds against E. coli and S. typhi, respectively, as well as tetracycline, 4-folds, against Klebsiella pneumonia in the presence of leaf extract of H. latifolia. Sub-inhibitory concentrations of H. latifolia and L. ovalifolia extracts reduced the activities of erythromycin and ciprofloxacin against all the test organisms. Sub-inhibitory concentrations of H. latifolia and L. ovalifolia extracts modified the activities of the selected antibiotics.

Key words: Minimum inhibitory concentration, antibiotics, microbial resistance, antibiotic-resistance modifying