## 3 Results and Discussion
### Identification of Test Microorganisms
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Name of Strain** & **Homology (\%)** & **Morphology** & **Gram Staining** & **Remark** & **Ref.** \\ \hline _Paenibacillus pasadenensis_ NBRC 161214 & 98 & Rods & Positive & Soil, water, sewage, etc. & [47] \\ _Microoccus yunmanensis_ YM 65004 & 99 & Cocci & Positive & Pollutants degradation & [49] \\ _Pseudomonas azotformus_ NBRC 12693 & 99 & Rods & Negative & Infection of cereal grains & [45] \\ _Rhodococcus qingshengii_ dj1-6-2 & 99 & Ovoid & Positive & Carbedazam degradation & [44] \\ _Sturblylococcus capitis_ sCM 2420 & 99 & Cocci & Positive & Human skin & [46] \\ _Sturblylococcus epidermidis_ NBRC 100911 & 98 & Cocci & Positive & Human skin & [46] \\ _Deinococcus radiodurans_ R1 & 99 & Cocci & Positive & Radiation resistance & [48] \\ \hline \end{tabular}
\end{table} 
Table 1: Isolated airborne bacteria and their characteristics. Conditions: The isolated strains were cultivated in sterile tryptic soy agar plates at 30 \({}^{\circ}\)C for 24 h. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Name of Strain**} & \multicolumn{5}{c}{**Antibacterial Activity**} \\ \cline{3-6}  & & **Hot Water** & **DMSO** & **Hexane** & **Ethanol** & **Methanol** \\ \hline
1 & _Paenibacillus pasadenensis_ NBRC 161214 & - & - & - & + & + \\
2 & _Microoccus yunmanensis_ YIM 65004 & - & + & - & + & + \\
3 & _Pseudomonas azotformus_ NBRC 12693 & - & - & - & - & - \\
4 & _Rhodococcus qingshengii_ dj1-6-2 & - & - & - & - & + \\
5 & _Sturblylococcus capitis_ JCM 2420 & - & - & - & - & - \\
6 & _Sturblylococcus epidermidis_ NBRC 100911 & - & - & - & - & - \\
7 & _Deinococcus radiodurans_ R1 & - & - & - & + & + \\ \hline \end{tabular} +: Positive effect; - negative effect.  
\end{table} 
Table 2: Screening of optimal solvents for antibacterial activity of _C. myrrha_ (T.Nees) Engl. resin extracts on isolated airborne bacteria. Conditions: The isolated strains were cultivated in sterile tryptic soy agar plates at 30 \({}^{\circ}\)C for 24 h.  
methanol (32.6) > ethanol (24.3) > hexane (1.89). The polarity index and dielectric constant of solvents are associated with the extraction of hydrophobic or hydrophilic compounds from raw materials (e.g., plants and fruits). [PERSON] and [PERSON] et al., measured the antibacterial efficiency of a _C. myrrha_ (T.Nees) Engl. resin extract using ethanol and methanol as extraction solvents, respectively, and found that only the ethanolic extract exhibited antibacterial activity against _Enterococcus faecalis_[26; 51]. Moreover, [PERSON] et al., and [PERSON] et al., also reported that the antibacterial effect of _C. myrrha_ resin extract was dependent on the polarity of the extraction solvent [30; 52; 53]. These results may be due to differences in solvent properties (polarity and dielectric constant) that affect the type of compound being extracted. When _C. myrrha_ (T.Nees) Engl. resin was extracted using hot water and ethanol, the quantity of extracted effective compounds containing carbohydrates, proteins, lipids, polyphenols, and alkaloids changed, which affected the antibacterial activity [29; 53]. These results imply that the quantity of some compounds (e.g., tannic acid, rutin, and quercetin as polyphenols) in the _C. myrrha_ (T.Nees) Engl. resin extracts obtained using methanol may be higher than those obtained using other solvents. Therefore, in the following experiments, methanol was used as the extraction solvent for _C. myrrha_ (T.Nees) Engl. resin because it yielded active compounds with the most potent antibacterial activity against the isolated airborne bacteria. Various polyphenols including tannic acid, rutin, and quercetin were observed as three major polyphenols in the _C. myrrha_ (T.Nees) Engl. resin extracts treated with methanol (Figure 1). [PERSON] et al., reported that tannic acid, rutin, and quercetin are effective against _Staphylococcus epidermidis_ and _Pseudomonas aeruginosa_[54]. In particular, tannic acid, a major compound of methanolic _C. myrrha_ (T.Nees) Engl.