reported that the production of diacetyl through citrate metabolism was dependent on the genus of bacteria and the growth conditions, while Christensen and Pederson (1958) has reported that the production of diacetyl was dependent on the different strains within the same species. The difference in concentrations of diacetyl in extracellular and intracellular extracts has been attributed to different efficiencies of transport across the cellular membrane. It has been reported that the limiting step for the utilization of citrate is the requirement for specific transporters, which facilitate its intake into the cells prior to production of diacetyl (Quintans et al.2008). Also, this limiting step and transport efficiency vary between microorganisms, which support the varying concentrations among the strains studied, for both intracellular and extracellular extracts. Our results showed that all strains were able to produce diacetyl at total concentrations ranging from 6.70 to 31.31 mg/mL. It has been reported that diacetyl exhibited antimicrobial activity against Gram-positive skin pathogens such as Staphylococcus aureus at concentrations as low as 3 mg/mL (Lanciotti et al.2003), indicating that the amount of diacetyl produced by our current strains of lactobacilli and bifidobacteria have the potential to exhibit dermal antimicrobial activities