Aggregation of Staphylococcus aureus following treatment with the antibacterial flavonol galangin
2007
Cushnie, T.P.T. | Hamilton, V.E.S. | Chapman, D.G. | Taylor, P.W. | Lamb, A.J.
Aim: The flavonol galangin, an antimicrobial constituent of the traditional medicines propolis and Helichrysum aureonitens, is being assessed as part of an ongoing investigation into the antibacterial activity of flavonoids. The present study sought to establish whether galangin has any aggregatory effect on bacterial cells. Methods and Results: In preparatory timeâkill assays, 50âμgâml−1 of galangin was found to reduce colony counts of c. 5â×â107âCFUâml−1Staphylococcus aureus NCTC 6571 by approximately 15â000âfold during 60 min of incubation. Subsequent light microscopy studies demonstrated significant increases in the number of large clusters of bacterial cells in populations treated with the flavonol. Conclusion: Data presented here show that galangin causes aggregation of bacterial cells. Significance and Impact of the Study: The finding that galangin causes bacterial cells to clump together may implicate the cytoplasmic membrane as a target site for this compound’s activity. More importantly, this observation indicates that decreases in CFU numbers detected in timeâkill and minimum bactericidal concentration (MBC) assays in previous investigations were at least partially attributable to this aggregatory effect. This raises the possibility that galangin is not genuinely bactericidal in action, and calls into question the suitability of timeâkill and MBC assays for determining the nature of activity of naturally occurring flavonoids.
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