European Journal of Medicinal Plants

Objective: Multiple drug resistant bacteria (MDR) are a global concern. This study investigates the possible broad-spectrum and synergistic antibacterial activities of ethanol leaf extracts of Psidium guajava and Platostoma africanum combinations on multi-drug resistant isolates.

Methods: The study used three (3) strains of extended spectrum beta lactamase (ESBL)-producing Escherichia coli, one non-ESBL-producing E. coli (control), 2 strains of methicillin resistant Staphylococcus aureus (MRSA) and one non-MRSA (control).The minimum inhibitory concentrations (MICs) of the plant extracts were determined against the test isolates using the agar dilution method. Assessment of synergism of the plant combinations against the test isolates was done by the checkerboard method. Their fractional inhibitory concentrations (FICs) indices were calculated and used to indicate synergism against the test organisms.

Results: P. guajava showed broad antibacterial activity against both groups of resistant organisms. P. africanum showed poor antimicrobial activity against the Gram-negative organisms compared to the Gram-positive strains. Determination of bactericidal activity of the extracts on the test isolates showed that the killing ability of the plants was time dependent. Most combination ratios of the plant extracts showed synergism against ESBL-producing E. coli strains and additivity against MRSA. The 8:2 (P. guajava: P. africanum) combination showed synergism against all the test isolates, with FIC indices ranging from 0.106 to 0.825.

Conclusions: P. guajava and P. africanum (8:2) combination has synergistic and broad spectrum antibacterial activity against ESBL-producing Escherichia coli and MRSA. The possibility of using the combination for disinfection is foreseeable. Characterization of the active principles from these plants is needed.