*3.2. Antimicrobial Activities of Isolated Compounds*

Antimicrobial activities of the purified compounds, except for the mixture of AB204-C (**3**) and AB204-D (**4**), were tested against four Gram-positive bacteria, five Gram-negative bacteria, two yeasts, and three fungi using paper disk diffusion assay with an equal amount of each compound at 50 μg/disk. The results are shown in Table 3. All compounds did not show activity against *E. coli* NIHJ, *K. pneumonia* ATCC 10031, *P. vulgaris* NBRC 3167, *Ps. aeruginosa* IFO 3080, and *Sa. cerevisiae* ATCC 9763. AB204-A (**1**) and B (**2**) displayed a weak activity towards *C. albicans* ATCC 64548, *A. niger* ATCC 6275, and *G. boninense* BCC 21330*,* with a clear zone range from 10.4 to 13.2 mm. However, they did not affect the Gram-positive and Gram-negative bacteria. AB204-E (**5**) and AB204-F (**6**) displayed no antifungal and antiyeast activities but showed good antibacterial activity against Gram-positive bacteria and weak activity against the Gram-negative bacterium *X*. *campestris* pv. *oryzae* KB88, which is a phytopathogenic strain. AB204-E (**5**) strongly inhibited *K. rhizophila* ATCC 9341, *B. subtilis* ATCC 6633, *M. smegmatis* ATCC 607, and *S. aureus* ATCC 6538p with inhibition zones of 41.3, 35.3, 32.7, and 26.0 mm, respectively, while AB204-F (**6**) showed a slightly lower activity against the same pathogens as is presented in Table 3. Anguinomycin A (**7**) revealed potent inhibitory activity against the Gram-positive bacterium *K. rhizophila* ATCC 9341 (19.1 mm), and two fungi, *Mu. racemosus* IFO 4581 (16.9 mm), and *G. boninense* BCC 21330 (19.6 mm), while leptomycin A (**8**) showed stronger activity against these pathogens at 30.6, 49.0, and 21.2 mm, respectively. Actinopyrone A (**9**) exhibited potent antifungal activity against *C. albicans* ATCC 64548 and three fungal strains with the inhibition zone in a range of 11.9 to 23.9 mm (Table 3). These results suggest that the antibacterial and antifungal activities of the *S. palmae* CMU-AB204T may have been displayed as a consequence of the contribution of all these antimicrobial secondary metabolites.

equal amount of each compound at 50 μg/disk. Inhibition zone (mm) (Mean ± SD; *n* = 3) including the diameter of the paper disk (8 mm) was measured after 24 and 48 h of incubation. **1**, AB204-A; **2**, AB204-B; **5**, AB204-E; **6**, AB204-F; **7**, anguinomycin A; **8**, leptomycin A; **9**, actinopyrone A.

**Table 3.** Antimicrobial activities of the pure compounds against fourteen microorganisms using an

