Synergic interaction between pomegranate extract and antibiotics against Staphylococcus aureus

We evaluated the interaction between Punica granatum (pomegranate) methanolic extract (PGME) and antibiotics against 30 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-sensitive Staphylococcus aureus (MSSA). Susceptibility testing of the isolates to PGME and antibiotics was performed by the broth dilution method. Synergic activity was detected between PGME and the 5 antibiotics tested, chloramphenicol, gentamicin, ampicillin, tetracycline, and oxacillin, ranging from 38% to 73%. For some isolates, PGME did not interfere with the action of any of the antibiotics tested. The bactericidal activity of PGME (0.1 x MIC) in combination with ampicillin (0.5 x MIC) was assessed using chosen isolates by time-kill assays, and they confirmed the synergic activity. Using this combination, cell viability was reduced by 99.9% and 72.5% in MSSA and MRSA populations, respectively. PGME increased the post-antibiotic effect (PAE) of ampicillin from 3 to 7 h. In addition, PGME demonstrated the potential to either inhibit the efflux pump NorA or to enhance the influx of the drug. The detection of in vitro variant colonies of S. aureus resistant to PGME was low and they did not survive. In conclusion, PGME dramatically enhanced the activity of all antibiotics tested, and thus, offers an alternative for the extension of the useful lifetime of these antibiotics.