title: Synergistic antibacterial effect between silibinin and antibiotics in oral bacteria.
abstract: Silibinin is a composition of the silymarin group as a hepatoprotective agent, and it exhibits various biological activities, including antibacterial activity. In this study, the antibacterial activities of silibinin were investigated in combination with two antimicrobial agents against oral bacteria. Silibinin was determined with MIC and MBC values ranging from 0.1 to 3.2 and 0.2 to 6.4  μg/mL, ampicillin from 0.125 to 64 and 0.5 to 64  μg/mL, gentamicin from 2 to 256 and 4 to 512  μg/mL, respectively. The ranges of MIC(50) and MIC(90) were 0.025-0.8  μg/mL and 0.1-3.2  μg/mL, respectively. The antibacterial activities of silibinin against oral bacteria were assessed using the checkerboard and time-kill methods to evaluate the synergistic effects of treatment with ampicillin or gentamicin. The results were evaluated showing that the combination effects of silibinin with antibiotics were synergistic (FIC index <0.5) against all tested oral bacteria. Furthermore, a time-kill study showed that the growth of the tested bacteria was completely attenuated after 2-6  h of treatment with the MBC of silibinin, regardless of whether it was administered alone or with ampicillin or gentamicin. These results suggest that silibinin combined with other antibiotics may be microbiologically beneficial and not antagonistic.
authors.affiliation: Department of Dental Hygiene, Sun Moon University, Asan-si 336-708, Republic of Korea.
authors.forename: Young-Soo
authors.initials: YS
authors.lastname: Lee
authors.forename: Kyeung-Ae
authors.initials: KA
authors.lastname: Jang
authors.forename: Jeong-Dan
authors.initials: JD
authors.lastname: Cha
mesh_terms: D000188:Actinobacillus / Q000187:drug effects; D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004357:Drug Synergism; D005839:Gentamicins / Q000494:pharmacology; D016965:Gram-Negative Anaerobic Straight, Curved, and Helical Rods / Q000187:drug effects*; D006801:Humans; D008826:Microbial Sensitivity Tests; D009055:Mouth / Q000382:microbiology*; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology*; D013291:Streptococcus / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D005839:Gentamicins; D012838:Silymarin; D000077385:Silybin; D000667:Ampicillin