# Anti-Yeast Synergistic Effects and Mode of Action of Australian Native Plant Essential Oils
## 3 Results
### Identification of the Main Bioactive Compounds in the Studied Eos  
The following compounds could be identified as the main 'bioactives' in the three Eos by GC-MS (qualitative analysis only): anethole (11.70 min) and methyl chavicol (10.11 min) in AM EO (Figure 6A), polygodial (20.03) and guaio1 (18.26 min) in TPL EO (Figure 6B), and neral (\(Z\)-isomer of citral; 10.84 min) and geranial (\(E\)-isomer of citral; 11.30 min) in LM EO (Figure 6C). Full chemical composition tests had been previously reported for commercially produced Eos of AM, TPL and LM and the results confirm our findings for the major identified bioactive compounds [18; 22; 31; 33]. There are two chemotypes of AM that contain the same compounds but at different ratios, especially between anethole and its isomer methyl chavicol. The first chemotype of AM EO consists of anethole (94.97%), methyl chavicol (4.43%), \(\alpha\)-pinene (0.09%), 1,8-Cineole (0.02%) and \(\alpha\)-farnesene (0.07%), and the second chemotype of AM EO has methyl chavicol (77.54%), anethol (19.95%), 1,8-Cineole (0.80%), \(\alpha\)-pinene (0.40%) and \(\alpha\)-farnesene (0.11%) [31; 33], C (C\({}_{10}\)H\({}_{12}\)O) and its isomer methyl chavicol (estragole) are phenylprogene aromatic compounds which were reported to possess antibacterial and antifungal properties [20; 41; 42; 43; 44; 45; 46; 47]. Our findings showed that the two major compounds in AM EO are similar to the first chemotype where anethole being the major component followed by its isomer methyl chavicol. A full chemical profiling of TPL EO showed the following sesquiterpene (C\({}_{15}\)H\({}_{24}\)) compounds: polygodial (36.74%), guaio1 (4.46%), calamenene (3.42%), pathulenol (1.94%), dirimenol (1.91%), cadina-1,4-diene (1.58%), 5-hydroxycalamenene (1.47%) bicyclogermacrene (1.15%), \(\alpha\)-cubebeene (0.88%), \(\beta\)-caryophyllene (0.87%), \(\alpha\)-copaene (0.48%), cadalene (0.44%), d-cadinol (0.40%), elemol (0.39%), T-muurolol (0.39%), germacrene-D (0.33%), and  
Figure 5: Scanning electron microscopic images of untreated _S. cerevisiae_ cells (**A**), and _S. cerevisiae_ cells treated with 0.5% (\(v/v\)) essential oils from anise myrtle (**B**), lemon myrtle (**C**) and Tasmanian pepper leaf (**D**).  
other sesquiterpenes compounds at levels below 0.16%, camphene, \(\alpha\)-gurjunene, and \(\beta\)-cubebene [22]. Our results of GC-MS qualitative analysis were in agreement with [PERSON] et al. [22] in which polygonal was the main compound in TPL EO followed by guaiol. Despite the fact that TPL EO contains some miner compounds in addition to its major constituent polygodial, most reports suggest that polygodial is the main contributor to the antibacterial and antifungal properties [18; 19; 20; 23; 48; 49; 50; 51; 52; 53; 54]. Plant Eos often contain several compounds where the antimicrobial activity arises from their major component; however, the minor compounds could form a complex synergistic interaction with the major compound, enhancing its antimicrobial action [55; 56; 57]. Previous chemical investigations reveal that LM EO predominantly (82-91%) consists of citral (C\({}_{10}\)H\({}_{16}\)O) which is a monoterpene aldehyde that exists in two isomers geranial (E-isomer or citral A) and neral (Z-isomer or citral B) [30; 58]. According to three separate chemical profiling investigations of LM, EO showed the following constituents: geranial (45-49%), neral (37-42%), 5-Hepten-2-one,6-methyl (1.54-13.82%), 2,3-Dehydro-1,8-cineole (3.52%), nerol (2.66%), Germacene B (0.2-2.18%), geraniol (0.8-1.26%), linalool (0.5-5.85%), myrcene (0.4-4.39%), and citronellal (0.25-2.19%) [30; 59; 60]. Our study showed the two major compounds in the tested LM EO are geranial and neral which is supported by the results reported by [PERSON] and [PERSON] [30], [PERSON] et al. [59], and [PERSON] [60]. The two major compounds geranial and neral (citral) contribute to the antimicrobial and antifungal activities in LM EO.