Inhibitory effect of emodin on MRSA biofilm and its mechanism

To investigate anti-biofilm activity and mechanisms of emodin against methicillin-resistant Staphylococcus aureus (MRSA) in vitro.

Microbroth dilution was explored to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of emodin against MRSA252 strain and clinical isolations. Inhibitory curve were draw to estimate dynamic bacteriostatic effect. Crystal violet staining was used to investigate the inhibitory effect of emodin against MRSA biofilm. The effect of emodin on the morphology of MRSA biofilm was observed by scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM). The expression of intercellular adhesion (ica) operon was detected by fluorescence quantitative PCR.

The MICs of emodin against different strains of MRSA ranged from 2 to 8 μg/mL, while MBCs were from 4 to 16 μg/mL. Emodin obviously inhibited the formation of biofilm in a dose-dependent manner. Besides, it destroyed biofilm structure and increased the ratio of dead bacteria under biofilm. Fluorescence quantitative PCR showed that emodin significantly down-regulated the expression of ica operon.

Emodin can inhibit MRSA biofilm in vitro, and may restrain the formation of bacterial biofilm by down-regulating the expression of ica operon.