# Bacteria Filtration Efficiency for Different Types of Protective Face Masks
## 3 Results and Discussion  
The data acquired from the investigation could determine which mask has the higher capacity or better efficiency in eliminating bioaerosols and optimal filtration of airborne particles. It seems that particle size distribution is an important factor influencing filtration efficiency determination, and it is necessary to determine the bacterial content of indoor air at educational facilities. To monitor the bioaerosol content of indoor air, as well as the bacterial and yeast filtration efficiency of the three different types of masks, air sampling at educational facilities was performed. A representative amount of air (250 L) was used to obtain a sufficient number of colonies for later identification. The number of total aerobic mesophilic bacterial colonies grown on TSA and chromogenic agar from analyzed locations A, B, C, and D after air filtration with the single-layer cloth, surgical, and FFP2 masks is presented in Figure 2a,b. As shown in Figure 2a, the largest number of mesophilic bacterial colonies was recorded in the control samples of each experimental group, which is in the air samples where the efficiency of mask filtration was not tested. Filtration efficiency was defined as the ability of the masks to retain bacteria, yeast, and mold and is expressed as a percentage compared with that of the control group. Analysis of the differences in colony number between the control and treatment using the different masks showed a statistically significant efficiency of bacterial filtration for all treatments (\(p<0.01\)). Among the masks tested, the single-layer cloth mask proved to be the least effective, retaining 28-78% of the mesophilic bacteria with the highest efficiency at location B (78%). On the other hand, the surgical and FFP2 masks showed a higher degree of filtration efficiency of the total aerobic mesophilic bacteria, from 93 to 98% and from 98 to 100%, respectively. The filtration efficiency of masks was also studied. Statistically significant filtering efficiency (\(p<0.01\)) was observed at all locations between the single-layer cloth mask and the surgical and FFP2 masks, as well as between the surgical and FFP2 masks. It is difficult to find many published investigations regarding testing mask filtration efficiency in comparison with available data regarding clinical trials and public health investigations. It has been reported that the use of single-layer cloth masks can result in significantly higher rates of infection than can the use of surgical masks, with this information being obtained from a randomized trial in healthcare workers [20; 21]. Figure 2: Number of grown colonies of (**a**) aerobic mesophilic bacteria on tryptic soy agar (TSA) and (**b**) yeasts and molds on Sabouraud agar (SA) from four locations (A, B, C, D) in the control group after air filtration with cloth, surgical, and filtering facepiece type 2 (FFP2) masks expressed as colony forming unit (CFU)/250 L of air. The data are presented as mean values of three determinations with standard deviations. Mean values marked with capital letter A represent significant differences between the control group and each treatment with cloth, surgical, and FFP2 masks, while lowercase letters a and b represent significant differences within treatments (\(p<0.01\); nonparametric Kruskal-Wallis [multiple comparisons] test). There are available data on fungi isolated from indoor environments [22], but information about yeasts and molds and their content in indoor air filtered through masks is insufficient. The filtration efficiency for yeasts and molds of protective mask was also investigated, and the results are shown in Figure 2b. As with the group of filtered mesophilic bacteria, all masks proved effective in retaining yeasts and molds. The highest filtration efficiency was achieved with the use of the FFP2 mask (94-100%) and the lowest with the single-layer cloth mask (13-79%).