Evaluation of antimicrobial potential of endophytic fractions of mentha piperita against pathogenic microbes

Endophytic microorganisms asymptomatically colonize healthy plant tissues and may be related to the plant's resistance to attack by pathogens or even to the synthesis of secondary metabolites. The present study was aimed at isolating and characterizing endophytic strains from the leaves, stems and roots (aerial and non aerial parts) of Mentha piperita (Lamiaceae). Coarse and fine leaves, stems and root fragments after surface sterilization with internal procedures were collected to isolate endophytes. After 10 days of incubation, the colonization rate (CR) of the fragments and the endophytic were purified and maintained in culture medium. The bacteria were partially characterized using Gram staining and fungi were identified by distinguishing between reproductive structures using a micro-culture technique. The endophytic CR was more significant in coarse root fragments. In roots, the percentage of bacteria was higher than the percentage of fungi while in leaves and stems, the percentage of fungi was higher in comparison to bacteria. Gram-positive bacilli (MPGPB) and gram positive coco-bacilli (MPGPCB) were accounted for the majority of bacterial isolates. Amongst all the fungal isolates, the majority had sporulating mycelium, which mainly consisted of fungi from the genus Penicillium, Fusarium, Trichoderma and Papulaspora. The antimicrobial activity of dominant endophytes were checked after preparation of solvent broth culture against test bacterial cultures viz. Bacillus subtilis, Bacillus licheniformis, Micrococcus luteus and Pseudomonas aeruginosa. The results were found to be very significant and surprising as all these endophytic solvent fractions showed potent antimicrobial activity against the test organisms.