# Antibiotic Resistance in Filters from Car Air Conditioning Systems
## 3 Results and Discussion
The study used the culture method, which, allowing to determine the abundance of culturable bacteria, is effectively used in quantitative studies of airborne microorganisms in the indoor environment, including the vehicles cabins [6; 9; 19; 21; 29]. Standard spread plate method was used by [PERSON] et al. [35], among others, to study the microflora present in dust from automotive cabin filters. They observed that bacteria isolated from filter dust from air conditioning system of cars operated in an urban area in Lahore, Pakistan, showed resistance to ampicillin and cefoxitin, while they were sensitive to ciprofloxacin [35]. \begin{table}
\begin{tabular}{c c c c c c c} \hline  & \multicolumn{2}{c}{**Bacteria in 26 \({}^{\circ}\)C (CFU/g)**} & \multicolumn{2}{c}{**Bacteria in 37 \({}^{\circ}\)C (CFU/g)**} & \multicolumn{2}{c}{**Molds (CFU/g)**} \\ \cline{2-7}  & **Average** & \begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} & **Average** & \
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} & **Average** &
\begin{tabular}{c} **Standard** \\ **Deviation** \\ \end{tabular} \\ \hline Toyota & 3.19 \(\times\) 10\({}^{6}\) & 7.27 \(\times\) 10\({}^{6}\) & 4.21 \(\times\) 10\({}^{4}\) & 7.84 \(\times\) 10\({}^{4}\) & 3.10 \(\times\) 10\({}^{4}\) & 3.59 \(\times\) 10\({}^{4}\) \\ Hyundai & 1.29 \(\times\) 10\({}^{6}\) & 1.59 \(\times\) 10\({}^{6}\) & 1.20 \(\times\) 10\({}^{5}\) & 0.23 \(\times\) 10\({}^{5}\) & 9.38 \(\times\) 10\({}^{4}\) & 9.19 \(\times\) 10\({}^{4}\) \\ Subaru & 4.26 \(\times\) 10\({}^{4}\) & 0.93 \(\times\) 10\({}^{4}\) & 1.43 \(\times\) 10\({}^{5}\) & 1.90 \(\times\) 10\({}^{5}\) & 9.07 \(\times\) 10\({}^{3}\) & 5.97 \(\times\) 10\({}^{3}\) \\ VW & 0.98 \(\times\) 10\({}^{6}\) & 1.49 \(\times\) 10\({}^{6}\) & 5.02 \(\times\) 10\({}^{4}\) & 6.18 \(\times\) 10\({}^{4}\) & 8.27 \(\times\) 10\({}^{4}\) & 5.80 \(\times\) 10\({}^{4}\) \\ Suzuki & 6.27 \(\times\) 10\({}^{5}\) & 8.34 \(\times\) 10\({}^{5}\) & 5.32 \(\times\) 10\({}^{4}\) & 9.17 \(\times\) 10\({}^{4}\) & 7.78 \(\times\) 10\({}^{4}\) & 5.77 \(\times\) 10\({}^{4}\) \\ \hline \end{tabular}
\end{table} 
Table 1: Average numbers of bacteria and molds in car cabin filters of individual car brands. Admittedly, a culture-based method, unlike molecular techniques, does not allow the assessment of the potential of spreading drug resistance due to gene transfer from dead bacterial cells [1]. It may also cause some problems with distinguishing between the transient and resident populations of antibiotic-resistant microorganisms [38]. On the other hand, there is evidence that the presence of a specific resistance determinant gene does not always result in a specific phenotypic effect. For example, it was found that a strain of _Pseudomonas fluorescens_ bacteria carrying the _van_B gene did not phenotypically show resistance to vancomycin, while _P. fluorescens_ and _P. aeruginosa_ equipped with the _qep_A gene nevertheless did not show phenotypic resistance to ciprofloxacin [6]. Obtaining antibiotic-resistant bacterial isolates in culture allows for their further testing to determine the resistance profile against selected antibiotics, which was also one of the areas of the present study. However, the optimal way seems to be a combination of the two approaches, which is confirmed by studies on not only cabin filters, but also filters from air conditioning systems in various types of objects. [PERSON] et al. [32] used a culture-based method combined with molecular analysis of fungal isolates in a study of automotive cabin filters (from 28 private cars and 19 cabs) used in urban areas in Portugal (three cities, including Lisbon). They revealed that slightly higher levels of bacterial contamination were found in cabs (up to \(4.7\times 10^{4}\) CFU/m\({}^{2}\)) than in private cars (up to1.7 \(\times\) 10\({}^{4}\) CFU/m\({}^{2}\)), with bacteria detected in more than 60% of taxis and more than 25% of private cars. Interestingly, no Gram-negative bacteria were detected in the filters tested.