Anti-biofilm activity of Rosmarinus officinalis, Punica granatum and Tetradenia riparia against methicillin-resistant Staphylococcus aureus (MRSA) and synergic interaction with penicillin

Abstract

The present study investigated the anti-staphylococcal effect of extracts of three species of plants (Rosmarinus officinalis, Punica granatum, Tetradenia riparia) against planktonic and biofilm cells of Staphylococcus aureus, including MRSA and MSSA. Minimal inhibitory and bactericidal concentrations (MIC and MBC) of hydroalcoholic extracts prepared with the leaves of R. officinalis and T. riparia, and peels of P. granatum were determined by the microdilution technique. Synergistic interactions between the extracts and penicillin were assessed by checkerboard method. The MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) reduction assay and scanning electron microscopy (SEM) were used to observe anti-biofilm effects. R. officinalis and T. riparia had good activity against S. aureus strains, with MICs in the range of 15.6–125 μg/ml. P. granatum was moderately active, with MICs of 125–250 μg/ml and MBCs of 500–1000 μg/ml. Synergistic effects occurred when the extracts were combined with penicillin. Anti-biofilm effects against pre-formed biofilms were observed at 30–250 μg/ml of R. officinalis and T. riparia extracts. SEM images showed a strong reduction of biofilm cells. The present results clearly show the anti-MRSA potential of R. officinalis, P. granatum and T. riparia when considering the planktonic and biofilm modes of bacterial growth, which may contribute to the development of new strategies against S. aureus and infections caused by this pathogen.