Synergy Between Plants Extracts and the Antibiotic Ciprofloxacin in Staphylococcus aureus

In recent years it has become increasingly difficult to combat bacterial infections resistant to antibiotics. The antibiotic Ciprofloxacin (Cip) is widely used for infections caused by Gram positive and Gram negative bacteria, however, its effectiveness has diminished in recent years due to the development of resistant isolates. In this study we survey plants for the presence of antimicrobial compounds and those that could synergize with Ciprofloxacin to inhibit the Cip resistant isolate Staphylococcus aureus 1199B. In addition, we aimed at finding the combination of solvents that could serve to separate antimicrobial compounds by thin layer chromatography. As part of a larger survey, twelve cultivated plants collected in the University of California, Irvine campus were studied for the presence of antimicrobial compounds and synergy with ciprofloxacin in S. aureus; these are Callostemon citrinus, Cistus crispus, Ginko biloba, Lophostemon confertus, Magnolia grandiflora, Pittosporium tobiri, Platanus mexicana, Prunus spp, Salvia fevelandi, Schefflera actnophylla, Schinus molle and Vinca major. In order to test if any of the extracted compounds from these plants had antimicrobial properties we conducted a series of bio-autographs and disk diffusion tests. We also tested the following combinations of solvents to separate active compounds of each plant species in bio-autographs: 4% methanol in dichloromethane, 100% dichloromethane, 65% ethyl acetate in hexane, 50% ethyl acetate in hexane, and 35% ethyl acetate in hexane. In our bio-autographs all 12 plants surveyed proved to have antimicrobial properties that inhibited the growth of S. aureus. For our disk diffusion tests the disks that contained the plant extracts with no added Cip had average inhibition zones of 9 mm. The disks that contained the plant extracts plus 4 µg/ml of Cip had average inhibition zones of 11.4 mm and the disks that had 5 µg/ml of Cip had average inhibition zones of 14.1 mm. All 12 plant extracts were able to inhibit the S. aureus but when adding Cip, the plant extracts more effectively inhibited S. aureus. However out of these 12 plants extracts the three that had the most synergy with Cip were Callostemon citrinus , Vinca majorwhich and Salvia fevelandi. This study showed that the 12 plant species studied contain antimicrobial properties and could synergize very successfully with Ciprofloxacin to inhibit Staphylococcus aureus. This research was supported by NIH Grant R25GM056647.