Antibacterial Activities of Bacterial Endophytes Isolated From Zataria multiflora, Achillea willhelmsii and Calendula officinalis L. Against Some Human Nosocomial Pathogens

Background Endophytes are microorganisms which live within plant tissues without causing any apparent harm to their host. Endophytes have been found in nearly all plant families and can be a source of metabolites that are potential source of antibacterial drugs. Objectives In this study, we focused on the isolation of bacterial endophytes from three medicinal plants; Zataria multiflora, Achillea willhelmsii and Calendula officinalis L. and screening them for activities against some human bacterial pathogens isolated from nosocomial infections. Methods In this descriptive study random samples from asymptomatic leaves and branches of three medicinal plants namely: Zataria multiflora, Achillea willhelmsii and Calendula officinalis L. were collected from Chaharmahal Va Bakhtiari province of Iran in spring 2013. For isolation of endophytic bacteria, the disinfected portions of the plants were distributed onto the isolation media. To examine endophytic bacterial contents, the bioassays were conducted with using growing colonies in peptone agar (PA) and yeast extract agar (YEA) media, then inactivated them by chloroform. To assay antibacterial activity of endophytic bacterial culture broth, filter-sterilized supernatants were poured in cylinders on each bacterial plate. Results Nine discernible bacterial endophytes were isolated in purification from three medicinal plants. Generally, all isolated endophytes showed acceptable effects against indicator bacteria, however endophytes isolated from Zataria multiflora and Achillea willhelmsii were more effective against Staphylococcus aureus than other endophytes. Conclusions Endophytes of examined medicinal plants could be a good source of antibacterial substances.