Antibacterial and antifungal activities of <i>Bacillus</i> RM-10 isolated from the Ngurah Rai Mangrove Forest

The escalating global health crisis due to antibiotic and antifungal resistance necessitates discovering novel antimicrobial agents. Extreme environment microorganisms, like those in mangrove soil, offer promising bioactive secondary metabolites. This study investigated the antibacterial and antifungal potential of Bacillus sp. RM10, an isolate from Ngurah Rai Mangrove Forest soil, via ethyl acetate extraction. Bacillus sp. RM10 was fermented in 100 mL ISP-2 liquid medium for 7 days. The supernatant was extracted twice with 100 mL ethyl acetate (1:1 v/v), and the extract was evaporated at 40°C. The viscous extract was tested against four bacteria ( Staphylococcus aureus ATCC 25923, Klebsiella pneumoniae ATCC 70060, Escherichia coli ATCC 25922, and Streptococcus mutans FNCC 0405) and two fungi ( Candida albicans and Aspergillus flavus ) using the Kirby-Bauer method. Results showed the ethyl acetate extract inhibited all tested microorganisms. Strong antibacterial activity was observed against S. aureus (15.00±1.30 mm), K. pneumoniae (14.50±0.90 mm), and E. coli (14.10±1.95 mm). Moderate inhibition was noted against S. mutans (9.00±1.43 mm). Strong antifungal activity was evident against C. albicans (10.50±1.40 mm) and A. flavus (10.80±0.60 mm). These findings confirm Bacillus sp. RM10 as a potential source of novel antibacterial and antifungal compounds, highlighting the therapeutic potential of mangrove ecosystems.