In vitro assessment of the antibacterial activity of combinations of methanolic extracts of Mangifera indica L. bark and Psidium guajava L. leaf on multidrug-resistant Pseudomonas aeruginosa

Pseudomonas aeruginosa causes various infections in humans both in hospital and community settings. Mangifera indica Linnaeus bark and dry Psidium guajava Linnaeus leaves have individually demonstrated activity against P. aeruginosa. This study aimed to assess the combined antibacterial activity of methanolic extracts of dry M. indica bark and dry P. guajava leaves on Multidrug-Resistant P. aeruginosa. Different proportion combinations of P. guajava and M. indica were assessed for antipseudomonal activity using Agar well diffusion method. Colistin was the positive control. The Fractional Inhibitory Concentration Index (FICI) was also determined. The combination of methanolic extracts of P. guajava leaves (35 mg/mL) and M. indica bark (6.25 mg/mL) had a superior antibacterial effect on Multidrug-Resistant P. aeruginosa when compared with the individual extracts used alone (p˂0.05), save for P. guajava (100 mg/mL) (p = 0.1373). Colistin was significantly more active on MDR P. aeruginosa than all the test extract concentrations used. This combination of M. indica bark and P. guajava leaves methanolic extracts had a FICI of 0.2434. This study demonstrates that the combination of P. guajava leaves (35 mg/mL) and M. indica bark (6.25 mg/mL) has synergistically enhanced activity against MDR P. aeruginosa. Keywords: Antipseudomonal, MDR Pseudomonas aeruginosa, Mangifera indica, and Psidium guajava