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. MIC 90, MIC 50, as well as MBC 90 and MBC 50, 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.
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 / Bernardetta, Segatore; Pierangelo, Bellio; Domenico, Setacci; F., Sbridelli; Nicoletti, Marcello; Marisa, Piovano; Juan A., Garbarino; Gianfranco, Amicosante; Mariagrazia, Perilli; C., Celenza. - In: PHYTOMEDICINE. - ISSN 0944-7113. - STAMPA. - 19:3-4(2012), pp. 341-347. [10.1016/j.phymed.2011.10.012]
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
NICOLETTI, Marcello;
2012
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. MIC 90, MIC 50, as well as MBC 90 and MBC 50, 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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
