Background: Biofilm inhibition in Staphylococcus epidermidis by an allicin solution in close but not direct contact with bacterial cultures was studied. A similar inhibition effect was observed when bacteria were replaced by papain, an enzyme with a sulfhydryl active center.Objectives: To explain these effects, a parallel assay was made with papain, a sulfhydryl enzyme, and allicin was placed in a separate well. After 1 hour of exposition time, a substrate was added to the papain solution and proteolytic activity was measured at regular time intervals to study possible enzymatic inhibition by allicin vapors.Materials and Methods: Growth and biofilm formation were measured according to established methods. These values were then averaged for the wells equidistant to a 3 mM allicin solution, and were related to the distance from the allicin well. Similar assays were performed with a solution of papain. After exposition to allicin vapors, a substrate was added and enzymatic activity was measured.Results: An inhibition effect was observed both in the bacterial cultures and the enzymatic solutions, and the extent of inhibition depended on the distance from the central well that contained the allicin solution.Conclusions: allicin vapor, or some decomposition product of allicin, causes inhibition of bacterial growth and biofilm formation.Parallel enzymatic studies confirmed this inhibitory effect and suggest that sulfhydryl enzymes are involved in biofilm formation in the strain studied.