# Antibiotic Resistance in Filters from Car Air Conditioning Systems
## 3 Results and Discussion  
Automotive cabin filters represent very good material for the study of microbial air pollution, because of the possibility of quantitative extraction of bioaerosol components from the filtration material [36]. This approach allows for the analysis of air conditioning systems working under actual operating conditions, with different strategies of system operation and under varying environmental parameters, thus positively influencing the reliability of the research results and the completeness of knowledge about the inhabiting microflora [22]. In this study, filters from cars of five different brands, obtained during periodic replacement of filters, were examined. The results of the quantitative assessment of the number of bacteria and fungi in the filters from each vehicle are shown in Figures 1 and 2, while their summary for each car brand is shown in Table 1.  
Figure 1: Bacterial counts in cabin filters of individual vehicles. Figure 2: Fungal counts in cabin filters of individual vehicles. A qualitative analysis showed that the number of bacteria growing at 26 \({}^{\circ}\)C varied greatly, even in the case of filters from vehicles of the same brand (Figure 1). For example, in Toyota cars, it ranged from 7.6 \(\times\) 10\({}^{3}\) to 1.8 \(\times\) 10\({}^{7}\) CFU/g of filter material (these were both the highest and lowest values of this parameter in this assessment). The bacterial concentrations were significantly higher than the bacterial numbers detected in cabin filters by [PERSON] et al. [32], which did not exceed 4.7 \(\times\) 10\({}^{4}\) CFU/m\({}^{2}\) of the filter. Similar discrepancies in terms of the level of microbial contamination were recorded for bacteria capable of growing at human body temperature, the content of which can provide indirect information on the presence of potentially pathogenic microorganisms. The abundance of bacteria growing at 37 \({}^{\circ}\)C was between 3.2 \(\times\) 10\({}^{2}\) and 4.7 \(\times\) 10\({}^{5}\) CFU/g. The large discrepancies in the results obtained for individual samples are reflected by the high standard deviation values for all tested car brands (Table 1). The quantitative analysis also covered the content of molds in the filters, showing the contamination of the filters with these microorganisms at a level of 10\({}^{3}\)-10\({}^{5}\) CFU/g, which is slightly lower than for the bacteria cultured at the same temperature (Figure 2). Existing literature data indicate that the dust collected from filters from air conditioning units may serve as test material providing important information on the nature and quantity of airborne pollutants [37]. It was shown that for automotive ventilation and air-conditioning systems, the culturable microbial counts in the dust were 4 \(\times\) 10\({}^{6}\) for bacteria and 5 \(\times\) 10\({}^{5}\) CFU/g for fungi [35]. The analogous values obtained by [PERSON] et al. [8] were 2.6 \(\times\) 10\({}^{4}\) CFU/g and 1.3 \(\times\) 10\({}^{4}\) CFU/g, respectively. The results obtained in the present study show that the analysis of fragments of filter material as a whole makes it possible to detect even more microorganisms than when analyzing dust from air-conditioning systems alone. A similar microflora extraction technique was used successfully in a study on cabin filters carried out by [PERSON] et al. [32]. In Poland, it is recommended to replace cabin filters after a mileage of 10-15 km or once a year [12]. The service life of the filters used in this study corresponds to these guidelines, as they were obtained during periodic (annual) vehicle inspections at authorized service centers for each brand. This makes it possible to estimate the comparatively highest level of filter contamination, at the end of their life, and possibly assess the resulting risks. The main objective of the present study was to assess the presence of bacteria showing resistance to several selected antibiotics in the tested cabin filters.