Synergism of Phyllanthus niruni Extract with Gentamicin against Methicillin Resistant Staphylococcus aureus

Aims: This study aimed to find out any synergism of gentamicin with the solvent extracts of small tropical herb Phyllanthus niruri to combat methicillin resistant Staphylococcus aureus.

Methodology: Bioactive constituents of Phyllanthus niruri were extracted by macerating ground dry powder of the leaves in water, n-hexane, chloroform, methanol and ethanol for 48-72 h followed by filtration and evaporation of solvents. Microdilution method was used to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of these extracts. The synergistic effects between gentamicin and the extracts were evaluated by the checkerboard assay to calculate the fractional inhibitory concentration index (FICI). In all cases, ten hospital associated MRSA strains were used.

Results: The MIC of aqueous and methanolic extracts of P. niruri against different MRSA strains varies from 3.125 mg/ml to 12.5 mg/ml. For the MRSA strain the combination of methanolic extract with gentamicin decreased the MIC of extract from 6.25 mg/ml to 0.2 mg/ml and the MIC of gentamicin from 2048 µg/ml to 256 µg/ml showing a strong synergistic effect with a fractional inhibitory concentration index of 0.157. Steroids, flavonoids, phenolic compounds and quinones identified in the extracts may play role in synergistic relation.

Conclusion: The present investigation shows that bioactive constituents from Phyllanthus niruri have an excellent synergy with gentamicin against MRSA and can be further explored as an alternative anti-staphylococcal agent.