## 4 Discussion
The highest E values for all species ranged from 0.584 to 0.725 and were obtained after 24 h of RCI application to the surface contaminated for 12 h (experimental variant I). On the contrary, a significant reduction was not observed on the glass surface covered with the contaminated meat sample during 72 h exposure of RCI (variant III). In this case, the meat sample placed on the glass surface created a favorable environment for bacterial growth, protecting the microorganisms from the harmful effect of RCI. The efficiency of radiant catalytic ionization is determined by a variety of factors, including type and physiological state of microorganisms, properties of the contaminated surface, environmental conditions, and parameters of the ionization process [26; 41; 42]. The sensitivity to irradiation is species- and strain-dependent and may be associated with the origin of the strain, the metabolic state of cells, and the ability to form biofilm [26]. The results obtained by [PERSON] et al. [40] suggest less sensitivity tophotohydroroionization of the non-antimicrobial resistant (non-AMR) _Salmonella_ strain compared to AMR _Salmonella_. Spore-forming bacteria and viruses are more resistant to radiant catalytic ionization [42]. According to [PERSON] et al. [43], the structural differences of Gram-positive and Gram-negative bacteria affect the resistance to ionization. It was found that \(S\). Typhimurium inoculated in pork jerky was more sensitive to EB-irradiation combined with the leak extract treatment than _L. monocytogenes_. On the contrary, in the study by [PERSON] et al. [42], _L. monocytogenes_ showed higher radiation sensitivity than _Salmonella_ spp. [PERSON] et al. [27] noted a similar level of _L. monocytogenes_ and \(S\). Enteritidis reduction after RCI treatment. [PERSON] et al. [28] observed lower sensitivity of _Escherichia coli_, as compared to _Listeria innocua_ and \(S\). Typhimurium after 60 min of RCI treatment; however, after 90 min no differences were reported. In the present study, in most cases, we observed no significant differences in the resistance to RCI exposure between _C. jejuni_, _L. monocytogenes_, and \(S\). Enteritidis. No statistically significant differences in the bacteria number reduction rate were noted for the strains of the same species, except for _C. jejuni_ in the experimental variant II. The time of ionization affects the irradiation efficiency and, generally, the greater reduction is associated with the longer time exposure [25; 28; 44]. According to [PERSON] et al. [45], approximately 75% of _B. subtilis_ spores were inactivated in 10 min, and about 90% after 30 min of photocatalytic oxidation. [PERSON] et al. [25] noted that RCI reduced microbial populations on stainless steel surfaces within 2 h and the greatest reduction was achieved after a 24 h treatment. The study of [PERSON] et al. [40] showed no differences in _Salmonella_ reduction resulting from the extension of photohydroroionization time from 15 to 60 s. Ionization time applied in our research ranged from 24 to 72 h. However, the longer exposition to RCI was applied to the surface covered with the contaminated meat sample during the whole experiment. The lower effectiveness of disinfection agents against bacterial biofilm compared to planktonic forms is a well-documented and undoubtful fact [26; 46; 47; 48; 49]. It is speculated that the biofilm extracellular polymeric substances (EPSs) may serve as the primary target of ROS and protect the associated bacteria cells [32]. Biofilm maturity is considered as an important factor affecting bacteria cell sensitivity to ionization. Biofilm formation is a four-stage biological process. In the initial stage, bacteria attach to the surface and next they proliferate, form microcolonies, and finally detach from the mature biofilm structure [50]. According to [PERSON] [51], ionizing radiation is more efficient against bacteria in the initial phase of attachment than in mature biofilm.