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

Objectives: This study examined antimicrobial potentials of endophytic bacteria isolated from leaf tissues of Hyptis suaveolens against some clinically significant pathogens. Methods: Endophytic bacteria were isolated from surface sterilized leaf fragments of Hyptis suaveolens. The isolates were grown in Nutrient Broth (NB) medium and medium amended with host plant extract. Antimicrobial activity was determined by spot inoculation and disc diffusion methods. Results: The result indicated that 60% of the isolates showed antimicrobial activity inhibiting at least one of the test pathogens in preliminary screening. Amongst the isolates, two bacterial 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 endophytic Bacillus and Pseudomonas species. The crude extracts exhibited moderate antibacterial and anti-candidal activity both by BLIS and agar diffusion assays. Enhanced antimicrobial activity was observed in nutrient broth medium amended with host plant extract. Spectrophotometric analyses of the crude metabolites of the 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. Conclusion: The study indicated that endophytic bacteria harbouring medicinal plants could be a potential source of antimicrobial agents.