Impact of luteolin on the production of alpha-toxin by Staphylococcus aureus

Aims: To investigate the influence of subinhibitory concentrations of luteolin on the production of alpha-toxin in Staphylococcus aureus. Methods and Results: The minimal inhibitory concentrations (MICs) were determined using a broth microdilution method, and the MICs of luteolin against the tested Staph. aureus strains ranged from 16 to 64 mu g ml(-1). Haemolysis, Western blot and real-time reverse transcription (RT)-PCR assays were used to evaluate the effect of luteolin on Staph. aureus alpha-toxin secretion and on the level of gene expression, respectively. The data indicated that subinhibitory concentrations of luteolin dose dependently decreased the production of a-toxin in both meticillin-sensitive Staph. aureus (MSSA) and meticillin-resistant Staph. aureus (MRSA). Furthermore, the transcriptional levels of agr (accessory gene regulator) in Staph. aureus were also inhibited by luteolin. Conclusions: Luteolin decreases the production and/or secretion of alpha-toxin in Staph. aureus; the reduced production may be dependent, in part, upon the luteolin-induced inhibition of the agr locus. Significance and Impact of the Study: The findings indicate that luteolin may be used as a basis for the development of antimicrobial agents aimed at bacterial virulence factors.