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Antibacterial effects of plant-derived extracts on methicillin-resistant Staphylococcus aureus.

Su XW, Howell AB, D'Souza DH
Foodborne Pathog Dis 9(6):573-8

Natural chemicals have been reported to have antibacterial effects against a variety of bacteria. The present study evaluated the antibacterial effects of commercially available grape-seed extract (GSE), pomegranate polyphenols (PP), and lab-prepared cranberry proanthocyanidins (C-PAC) against two strains of methicillin-resistant Staphylococcus aureus (MRSA). GSE, PP, and C-PAC at concentrations of 2 mg/mL, 10 mg/mL, or controls were mixed with equal volumes of overnight cultures of MRSA at ~6 log10 colony-forming units (CFU)/mL and incubated for 0, 1, 2, 8, and 24 h at 37 degrees C. Treatments were neutralized/stopped using tryptic soy broth containing 3% beef extract. Serial dilutions of the treated MRSA strains and controls were spread-plated on trypticase soy agar and incubated for 24-48 h at 37 degrees C and colonies were counted. Among the three tested agents, GSE at 1 and 5 mg/mL was found to be most effective against MRSA, resulting in a 2.9-4.0 log10 CFU/mL reduction of both strains after 2 h at 37 degrees C. PP at 1 and 5 mg/mL was found to cause 1.1-2.3 log10 CFU/mL reduction, while C-PAC at 1 mg/mL caused