Subinhibitory concentrations of licochalcone A decrease alpha-toxin production in both methicillin-sensitive and methicillin-resistant Staphylococcus aureus isolates.

To evaluate the effect of subinhibitory concentrations of licochalcone A (LicA) on alpha-toxin secretion in Staphylococcus aureus. A haemolysin assay was used to investigate the haemolytic activities in culture supernatants of both methicillin-sensitive and methicillin-resistant Staph. aureus isolates cultured with graded subinhibitory concentrations of LicA. Alpha-toxin secretion was detected by immunoblot analysis. Moreover, quantitative RT-PCR was performed to assess the influence of LicA on the transcription of hla (the gene encoding alpha-toxin) and agr (accessory gene regulator). Growth in the presence of LicA markedly inhibited the mRNA levels of hla and agr in Staph. aureus, resulting in a reduction of alpha-toxin secretion and, thus, haemolytic activities. The secretion of alpha-toxin in Staph. aureus is decreased by LicA; this effect may be partially dependent upon inhibition of the Agr two-component system. The findings in our study may support the use of LicA as a lead compound in the design of more potent antibacterial agents that are based on the chalcone template.