# Cotton Terry Textiles with Photo- and Bio-Activity in a Model Study and Real Conditions
## 4 Discussion
The model studies in this paper concerning _E. coli_ bacteria incubated on the modified textiles in conditions of visible light and RH = 43% confirmed a minor increase in biostatic activity (A = 1), compared to conditions of darkness and high humidity RH = 80% (A = 0.9), which may support the direct biocide impact effect through photocatalytic processes induced by visible light. The antimicrobial activity in the model conditions was low or medium. It can be considered only as biostatic effect, no biocidal effect was obtained, which requires reduction of 2 log reduction. Microorganisms survived on textiles in model conditions much better than in real conditions. The survival of microorganisms on bioactive textiles in model conditions depends on many factors, one of them is strain sensitivity, the presence of additional nutrients in the form of residues laboratory medium, optimal growth conditions (temperature, humidity) that have a protective effect on microorganisms compared to real conditions (environmental strains, lack of nutrients, various climatic conditions). Currently, emphasis is placed on new photocatalytic solutions, e.g., using two kinds of photocatalysts as nanoparticles that will be photocatalystly active in visible light [52; 53; 54]. Thus, in the present studies, the tested textile fabric was modified with TiO\({}_{2}\) and ZnO nanoparticles. Light activates photocatalytic processes, contrary to the direct biocide action mechanism. The photocatalysis mechanism is mainly based on the formation of ROS, which draws out the hydrogen atoms from C-H bonds or attacks the unsaturated chemical bond [55]. ROS oxidizes proteins and lipids in cell envelopes and leads to changes in the cell surface and the release of ions from microorganism cells [56; 57]. Another mechanism, which can be responsible for cell death, is oxidation of the intracellular coenzyme A (CoA), which inhibits cell respiration [50] and attacks intracellular components directly causing alteration of the protein structure [58]. To date, there is no mention in the literature of textiles with photocatalytic properties in visible light under real conditions. For this reason, this paper focuses on testing an industrial solution (Polish Patent Application No P.433366) in cooperation with a towel manufacturing company. The tests were conducted in two types of bathrooms used by a similar number of people. The lighting and air humidity in the bathrooms were different. In the bathroom with artificial lighting the conditions were as follows: average air humidity RH = 65.6-66.8%, temp. 21 \({}^{\circ}\)C, light intensity 152.8-166.7 lux and lighting time 80.7-87.8 min/day. In the bathroom with natural lighting the following conditions were met: average RH = 36-44.5%, temp. 23 \({}^{\circ}\)C, light intensity 92.3-95.0 lux and lighting time 420 min/day. On the surface of the modified towels after seven days of use, a high reduction in the number of microorganisms was observed, especially for _Enterobacteriaceae_, _Enterococcus_, coli group and _E. coli_ and _Pseudomonas_. The number of microorganisms decreased from \(10^{1}\)-\(10^{6}\) CFU/cm\({}^{2}\) to 0-5 CFU/cm\({}^{2}\), which denotes their almost complete removal. Biological activity towards these groups of microorganisms has also been demonstrated in the literature in the model studies of different photocatalytic systems [16; 32]. The identification of microorganisms isolated from the surface of the towels modified with TiO\({}_{2}\) and ZnO after seven days of use revealed that _Staphylococcus_ (_S. hominis, S. xylosus, S. saprophyticus, S. lentus, S. warneri_) and _Kocuria variants_ were the dominating bacteria. These occur naturally in the skin microflora (_Staphylococcus_) and in the air (_Kocuria_), and can be less sensitive to the direct impact of biocides and photocatalytic processes than _Enterobacteriaceae_, _Enterococcus_, coli group and _E. coli_ and _Pseudomonas_.