Antimicrobial Activity of the Rhizospheric Bacillus Species Isolated from Potato (Solanum tuberosum) Organic Farm Soils in the Philippines

Abstract

The purpose of this study is to determine the potential of rhizospheric bacteria belonging to the genus Bacillus isolated from the organic soil of Solanum tuberosum (potato) as an untapped and promising source of novel antimicrobials to combat infections, particularly multidrug-resistant strains.

The rhizospheric Bacillus species were isolated using serial dilution and aerobic cultivation. Hydrolytic exoenzyme production was determined using plate techniques, whereas antimicrobial activity was determined using the cross-streak method and agar-disc diffusion assay. The data indicate that the Bacillus isolates possess antimicrobial property against gram-positive bacterial pathogens. The activities were compared to those of the antibiotic Rifampicin as a control. Notably, several Bacillus isolates inhibited the growth of methicillin-resistant Staphylococcus aureus (MRSA). The top performing Bacillus isolates were identified by 16s rRNA gene sequence analysis, which showed the similarities of the isolates to known soil-associated and plant-growth-promoting species; B. velezensis, B. mojavensis, B. subtilis, B. sonorensis, B. tequilensis, B. clausii, B. amyloliquefaciens, B. altitudinis, and B. siamensis from those sequences available in GENBANK.

The present investigation establishes the presence of antagonistic Bacillus species in S. tuberosum's rhizosphere. The findings may form the basis for further investigation of the active compounds produced by the isolates and the mechanisms underlying their antimicrobial activity, while optimizing the culture medium for efficient production of potent antimicrobial compounds to combat infectious agents may further be investigated.