Aims: To investigate the antibiofilm effect of cinnamaldehyde on methicillin-resistant Staphylococcus aureus (MRSA) and analyse the effect of subminimum inhibitory concentrations (MICs) of cinnamaldehyde on the expression of the biofilm-related gene sarA.
Methods and results: The MICs and minimum bactericidal concentrations (MBCs) were determined using a microtitre broth dilution method. Biofilm susceptibility was determined using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) staining and colony forming unit (CFU) counting assays. Antibiofilm effects were studied with scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM). SarA expression was assessed by real-time PCR. MICs and MBCs were in the range 0.0625-0.5% (v/v). The killing effects were concentration dependent. At a concentration of 5× MIC, all strains in biofilm were decreased to lower than 20% of the control groups. SEM and CLSM images indicated that a 5× MIC concentration of cinnamaldehyde was able to detach and kill existing biofilms. Apart from strain JB-06, real-time PCR showed that the expression of sarA of all other strains was decreased upon exposure to sub-MICs of cinnamaldehyde.
Conclusions: These data showed the strong killing effect of cinnamaldehyde against MRSA within biofilms.
Significance and impact of the study: This study indicated the potential of cinnamaldehyde as an inhibitory agent for use in MRSA biofilm-related infections.
© 2011 The Authors. Letters in Applied Microbiology © 2011 The Society for Applied Microbiology.