Bioactivities of bacterial endophytes isolated from leaf tissues of Hyptis suaveolens against some clinically significant pathogens

This study examined the antimicrobial potentials of endophytic bacteria isolated from leaf tissues of Hyptis suaveolens against some clinically significant pathogens. The results indicated that 60% of the isolates showed antimicrobial activity inhibiting at least one of the test pathogens in preliminary screening. Among them two isolates showed considerable antimicrobial activity against the test pathogens. The isolates were identified as Bacillus and Pseudomonas species by morphological and biochemical characterization. Phylogenetic analysis of 16S rDNA sequences of the isolates showed closest homolog to an endophytic Bacillus amyloliquefaciens and an endophytic Pseudomonas sp. suggesting their endophytic nature. The crude ethyl acetate extracts prepared from fermentative broths exhibited moderate antibacterial and anticandidal activity both by BLIS and agar diffusion assay. Enhanced antimicrobial activity was observed in nutrient broth medium amended with host plant extract. Specrophotometric analysis of the crude metabolites of isolates indicate presence of bioactive component. The metabolite obtained from Bacillus sp. showed a λ-max of 1.541 at 254 nm and that of Pseudomonas sp. was 0.155 at 250 nm. Our study suggests that endophytic bacteria residing in medicinal plants could be a potential source of antimicrobial agents.