Aims: The aim of this study is to determine the in vitro activity of allicin against Staphylococcus epidermidis and to evaluate the influence of allicin on biofilm formation. Methods and Results: In vitro activity of allicin (diallyl thiosulphinate) against 38 strains of S. epidermidis was investigated. The activity of allicin was similar against S. epidermidis methicillin susceptible and methicillin resistant strains [minimum inhibitory concentration (MIC) 90 ¼ 8 mg l)1 ]. In general, subinhibitory concentrations (sub-MIC) of allicin diminished biofilm formation in the five strains analysed. Conclusion:The results confirm the antibacterial effect of allicin. Sub-MICs of allicin also diminished the biofilm formations by S. epidermidis. Significance and Impact of the Study: The present study shows that allicin is active in vitro against S. epidermidis and that sub-MICs of allicin may play a role in the prevention of adherence of this bacteria to medical devices.

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Aims:  Polysaccharide intercellular adhesin (PIA) is the main agglutination agent in the biofilm forming strain Staphylococcus epidermidis. To find an explanation for the observed inhibition of biofilm formation by allicin, we studied the effect of allicin on PIA production in samples treated with sub MIC doses of allicin and compared this with a control culture without allicin. Methods and Results:  Bacteria (Staph. epidermidis ATCC 35984) were grown in glass tubes, and PIA was extracted by vortex vibration using microbeads and NN dimethyl acetamide/LiCl as solvent. The extracts were filtered and passed through size exclusion columns. Chromatographic fractions were analysed with an excess of sodium metaperiodate and the excess was determined spectrophotometrically using 2,4,6‐tripyridyl‐s‐triazine. Conclusion:  The amount of exopolysaccharides in samples previously treated with allicin is significantly lower than in the control. This finding suggests a specific enzymatic inhibition in PIA synthesis. Significance and Impact of the Study:  This study provides an insight into the mechanism of biofilm formation, and is a biochemical model for PIA inhibition by allicin. The analysis proposed may be useful in studies of production of exopolysaccharides responsible for adherence and agglutination of Staph. epidermidis. Prevention of biofilm formation by allicin opens up a new field of in vitro studies and permits us to envisage future clinical applications.

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I described a method based on the oxidation of diallyl disulfide with magnesium monoperoxyphthalic salt (MMPP) (1) and tetrabutylammonium hydrogen sulfate (TBHS) as phasetransfer reagent. Because the reaction yield was poor, I studied the phasetransfer process; the results show that, at room temperature, the quaternary ammonium salt behaves as a surfactant or carrier rather than as a catalyst. The overall yield depends on the initial ratio [carrier]/[oxidant]. The synthesis method has therefore been modified and simplified as described below.MMPP, at 20% molar excess over the disulfide, and TBHS, at 2.5-fold the oxidant concentration, were dissolved in 50 mL of water at pH 4.6. Allyl disulfide, 1 g, was dissolved in 25 mL dichloromethane. The two-phase mixture was stirred at 200 rpm for 35 min in an ice bath. The yield of allicin was nearly 50%. The organic phase was filtered at Ϫ50°C, making unnecessary the previously used extraction with ammonium bicarbonate. Under these conditions, the products can be separated by thin-layer chromatography without the previously used step of concentration with a stream of nitrogen.