RESULTS

Minimum Inhibitory Concentration

The results obtained are reported in tables and charts showing the ability of the formulation to reduce the microbial load after the incubation of each strain with the tested solution at different dilutions.

In Figure 1. the delta of absorbance is reported, which represents the optical density of each strain for each dilution of the tested product.

 
Figure 1. Analysis of the microbial inhibition after incubation with the tested product. Microbial strains: S. aureus (ATCC 6538), S. epidermidis (ATC 12228), E. coli (ATCC 8739), P. aeruginosa (ATCC 9027), C. albicans (ATCC 10231 and A. brasiliensis (ATCC 16404)).
 
As shown, all the samples show a similar trend, with the progressive reduction of the inhibitory activity of microbial growth versus the dilution of the product.
 
Table 1. summarizes the data represented above, reporting the minimal dilution that inhibit the growth of the bacterial culture. A higher dilution value corresponds to a higher efficacy of the product.
   Tested strains MIC
   S. aureus 11.1%
   S. epidermidis 11.1%
   P. aeruginosa 3.7%
   E. coli 11.1%
   C. albicans 11.1%
   A. brasiliensis 11.1%

Table 1. Minimum inhibitory concentration that show a bacteriostatic action against the bacterial strains selected.

Minimum Bactericidal Concentration

The results obtained are provided in tables and charts showing the first concentration able of inducing a 99.9% reduction of the bacterial load of each strain selected and treated with the products to be analysed at the different dilutions tested.

Furthermore, the standard method was applicated for all reference strains and the results obtained from the analysis were compared in order to identify the strains most sensitive to the bactericidal activity of the medical device.

In Figure 2. images of the subcultures obtained from the three selected concentrations and the relative control are shown.

Figure 2. MBC identification (in red) between the three concentrations tested respect to control, after the incubation of the medical device with 106 CFU/ml of the selected strains (S. aureus (ATCC 6538), S. epidermidis (ATC 12228), E. coli (ATCC 8739) and P. aeruginosa (ATCC 9027) and incubation with 105 CFU/ml of C. albicans (ATCC 10231) and A. brasiliensis (ATCC 16404), during the MIC assay.

All the samples show a similar trend, with a 99.9% reduction of the microbial load at the same dilution except for P.aeruginosa, C. albicans and A. brasiliensis which proved to be more sensitive to the product than the other strains.

The Table 2. summarizes the above graphically represented data, reporting the minimum bactericidal concentration able of determining a 99.9% reduction in bacterial growth.

MICROBIAL STRAINS MBC
S. aureus 33.3%
S. epidermidis 33.3%
P. aeruginosa 11.1%
E. coli 33.3%
C. albicans 11.1%
A. brasiliensis 11.1%

Table 2. Cosmetic product concentrations able to determine a bactericidal activity (99.9% reduction of microbial load).