title: In vitro interaction of usnic acid in combination with antimicrobial agents against methicillin-resistant Staphylococcus aureus clinical isolates determined by FICI and ΔE model methods.
abstract: The in vitro antimicrobial activities of usnic acid were evaluated in combination with five therapeutically available antibiotics, using checkerboard microdilution assay against methicillin-resistant clinical isolates strains of Staphylococcus aureus. MIC₉₀, MIC₅₀, as well as MBC₉₀ and MBC₅₀, were evaluated. A synergistic action was observed in combination with gentamicin, while antagonism was observed with levofloxacin. The combination with erythromycin showed indifference, while variability was observed for clindamycin and oxacillin. Data from checkerboard assay were analysed and interpreted using the fractional inhibitory concentration index (FICI) and the response surface approach using the ΔE model. Discrepancies were found between both methods for some combinations. These could mainly be explained by the failure of FIC approach, being too much subjective and sensitive to experimental errors. These findings, beside confirm the well known antimicrobial activity of usnic acid, suggest, however, that this substance might be a good candidate for the individuation of novel templates for the development of new antimicrobial agents or combinations of drugs for chemotherapy.
authors: Department of Biomedical Sciences and Technologies, University of l'Aquila, L'Aquila, Italy.
authors: Bernardetta
authors: B
authors: Segatore
authors: Pierangelo
authors: P
authors: Bellio
authors: Domenico
authors: D
authors: Setacci
authors: Fabrizia
authors: F
authors: Brisdelli
authors: Marisa
authors: M
authors: Piovano
authors: Juan A
authors: JA
authors: Garbarino
authors: Marcello
authors: M
authors: Nicoletti
authors: Gianfranco
authors: G
authors: Amicosante
authors: Mariagrazia
authors: M
authors: Perilli
authors: Giuseppe
authors: G
authors: Celenza
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001572:Benzofurans / Q000494:pharmacology*; D002981:Clindamycin / Q000494:pharmacology; D003470:Culture Media / Q000737:chemistry; D024901:Drug Resistance, Multiple, Bacterial; D004357:Drug Synergism; D004917:Erythromycin / Q000494:pharmacology; D005839:Gentamicins / Q000494:pharmacology; D064704:Levofloxacin; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000254:growth & development; D008826:Microbial Sensitivity Tests / Q000379:methods*; D008954:Models, Biological; D015242:Ofloxacin / Q000494:pharmacology; D010068:Oxacillin / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001572:Benzofurans; D003470:Culture Media; D005839:Gentamicins; C073339:usnic acid; D002981:Clindamycin; D004917:Erythromycin; D064704:Levofloxacin; D015242:Ofloxacin; D010068:Oxacillin