Evauation of the Minimum Inhibitory Concentration (MIC) and the Minimum
Bactericidal Concentration (MBC)

The results obtained are reported in tables and pictures showing the ability of the cosmetic preservative to reduce the microbial load after the incubation of each strain with the tested solution at different dilutions. The MIC was visually evaluated in the 96well plate and after, the identified concentration (MIC) and following concentrations (increasing and decreasing with respect to the MIC) were plated in the specific strain growth conditions.
In Figure 1 pictures of the subcultures obtained from the three selected concentrations and represented the first bacteriostatic and bactericidal concentration and the relative control for each strain selected are shown.

Figure 1. MIC identification (in blue) and MBC identification (in red) between the three concentrations tested respect to control, after the incubation of the cosmetic preservative with 10^6 CFU/ml of the selected strains S. aureus (ATCC 6538), S. epidermidis (ATCC 12228), E. coli (ATCC 8739) and P. aeruginosa (ATCC 9027) and incubation with 10^5 CFU/ml of C. albicans (ATCC 10231) and A. brasiliensis (ATCC 16404), during the MIC assay.
All the samples show a 99.9% reduction of the microbial load at different dilutions, in particular P.aeruginosa proved to be more sensitive to the cosmetic preservative than the other strains.
The Table 1 summarizes the above graphically represented data, reporting the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) able of determining a 99.9% reduction in bacterial growth.

Table 1. Cosmetic preservative concentrations able to determine a bacteriostatic and bactericidal activity against the selected strains