## 3 Results and Discussion  
### Main Results of the In Vitro Studies  
As an example, Figure 5 shows the results of microbiological experiments assessing the bactericidal effectiveness of the \"Zarnitsa-A\" apparatus against _Pseudomonas aeruginosa_ and _Staphylococcus aureus_ bacteria. The experimental data are represented as a dependence of the logarithm of inactivation on the energy dose of UV-C radiation (the so-called survival curves) and show that the \"Zarnitsa-A\" apparatus deeply disinfected a surface contaminated with bacteria at doses of \(\sim\)25 mJ/cm\({}^{2}\), approximately corresponding to one minimum erytmal dose (MED); a decrease in surface contamination of more than five orders of magnitude was achieved (the disinfection efficiency exceeded 99.999%). Similar results were obtained for the other bacteria--_Escherichia coli_ and _Streptococcus pyogenes_. No statistically significant differences in the resistance of the selected MOs to high-intensity optical radiation were found over the course of the experiments. Increasing the dose to 150 mJ/cm\({}^{2}\) led to the almost complete sterilization of the surface (we observed the absence of colony growth or single colonies). However, with an increase of more than 25 mJ/cm\({}^{2}\) in the energy dose, the rate of decrease in the level of infection (inactivation rate) decreased, and the survival curves tended to saturate or reach a plateau. This type of survival curve is determined based on the heterogeneity of the irradiated bacterial population, i.e., the presence of a fraction of microorganisms resistant to a disinfecting factor (in this case, UV radiation). The formation of a \"tail\" in the survival curve may be due to factors of a nonbiological nature, in particular, the mutual shading of bacteria at their high surface densities, which is characteristic of the conditions of the experiments. Experimental data representing the bactericidal effectiveness of the \"Zarnitsa-A\" apparatus at various doses of UV-C radiation are shown in Figure 6.  
Figure 5: Logarithmic depiction of _Pseudomonas aeruginosa_ (1) and _Staphylococcus aureus_ (2) bacteria inactivation using the “Zarnitsa-A” apparatus. The initial densities of the bacterial load on the surface of the agar were \(N_{0}\)(1) = 4\(\cdot\)10\({}^{5}\) and \(N_{0}\)(2) = 2\(\cdot\)10\({}^{6}\) (2) CFU/cm\({}^{2}\). The graph shows the standard deviations (SD) in the area of low and high doses. Considering that the microbiological measurements in this methodology had an error within one order, it should be stated that the \"Zarnitsa-A\" apparatus had approximately the same bactericidal effectiveness regarding all the studied MOs--_Escherichia coli_, _Pseudomonas aeruginosa_, _Staphylococcus aureus_, and _Streptococcus pyogenes_. In a 10-s irradiation session at a distance of 10 cm from the emitter of the device to the contaminated surface, the level of bacterial contamination for all the indicated microflora decreased by more than five decimal orders; the disinfection efficiency exceeded 99.999%. At a UV-C radiation dose of D = 150 mJ/cm\({}^{2}\) (three irradiation cycles of 20 s each), the reduction in agar surface contamination for all considered microorganisms exceeded a million times (inactivation logarithm, \(lg(N_{0}/Ni)>6\)). Reducing the distance to \(\sim\)5 cm increased the power density of the UV radiation on the object by about a factor of two, which made it possible to halve the duration of the disinfection process (in particular, to 5 s while maintaining the energy dose of irradiation at \(\sim\)25 mJ/cm\({}^{2}\)). Thus, the experiments show the high bactericidal effectiveness of the \"Zarnitsa-A\" apparatus and the possibility of a significant reduction in the duration of preventive and therapeutic procedures. In this work, microorganisms whose drug resistance had not been studied were mainly used.