Anti-Biofilm Activity of Grapefruit Seed Extract against <i>Staphylococcus aureus</i> and <i>Escherichia coli</i>.

Abstract

Grapefruit seed extract (GSE) is a safe and effective preservative that is used widely in the food industry. However, there are few studies addressing the anti-biofilm effect of GSE. In this study, the anti-biofilm effect of GSE was investigated against biofilm-forming strains of <i>Staphylococcus aureus</i> and <i>Escherichia coli</i>. The GSE minimum inhibitory concentration (MIC) for <i>S. aureus</i> and <i>E. coli</i> were 25 μg/ml and 250 μg/ml, respectively. To investigate biofilm inhibition and degradation effect, crystal violet assay and stainless steel were used. Biofilm formation rates of four strains (<i>S. aureus</i> 7, <i>S. aureus</i> 8, <i>E. coli</i> ATCC 25922, and <i>E. coli</i> O157:H4 FRIK 125) were 55.8%, 70.2%, 55.4%, and 20.6% at 1/2 × MIC of GSE, respectively. The degradation effect of GSE on biofilms attached to stainless steel coupons was observed (≥ 1 log CFU/coupon) after exposure to concentrations above the MIC for all strains and 1/2 × MIC for <i>S. aureus</i> 7. In addition, the specific mechanisms of this anti-biofilm effect were investigated by evaluating hydrophobicity, auto-aggregation, exopolysaccharide (EPS) production rate, and motility. Significant changes in EPS production rate and motility were observed in both <i>S. aureus</i> and <i>E. coli</i> in the presence of GSE, while changes in hydrophobicity were observed only in <i>E. coli</i>. No relationship was seen between auto-aggregation and biofilm formation. Therefore, our results suggest that GSE might be used as an anti-biofilm agent that is effective against <i>S. aureus</i> and <i>E. coli</i>.