Antimicrobial activity of natural soaps tested by Bioscreen methodology

The aim of this study was to combine the utilization of waste frying oils within soap making process in order to make useful and environmentally friendly solutions and development of methods for determination of the antimicrobial effect of those created products. Soaps were made from edible oils which are fried in laboratory conditions. The antimicrobial activity of soaps was done against Staphylococcus aureus species as one of the representatives of the human skin microbiome. Two methods were applied: agar dilution method and the method including kinetics following on Bioscreen micro­biology reader. In the first method, the number of CFU was followed on agar medium with and without different soap solutions after incubation for 24 hours at 30 °C. The result for IC50 (inhibition concentration for 50% of population) was 0.08 mg/mL. Minimal inhibition concentration was detected at 0.41 mg/mL and minimal bactericidal concentration was observed at > 0.75 mg/mL for selected soap solution. Soap concentrations of 0.3 mg/mL of soaps (made from fresh and fried oil) were used for Bioscreen assessment with measurement on every hour during the 7 hours of incubation at 30 °C. 5-second sequence of shaking of the microplate was applied before each measurement which was done at the wavelength of 610 nm. The growth coefficients of the culture with soap solutions added and from the growth of culture only were compared. The growth of S. aureus subjected to soaps made from fresh and fried oils was inhibited 55.3% and 69.7% respectively against the control during the first seven hours of incubation. From results obtained, it was concluded that there is a great potential of the Bioscreen as a method for further studies on antibacterial activity of soaps made from waste frying oils