The use of antibiotics has unleashed high bacterial resistance. This outcome triggered the urgent need for effective new antibacterial agents to treat infectious diseases. A promising source for the production of antibiotics and several other bioactive substances are endophytic fungi. These microorganisms inhabit in and bring benefits to living plant tissues. Thus, the aim of this paper was to know the endophytic fungi associated with Oryctanthus alveolatus (mistletoe) and assess their potential to inhibit pathogenic bacteria. A total of 86 endophytic fungi were isolated from the stems and leaves of O. alveolatus. Of these fungi, 29 were selected for the assessment of antimicrobial activity. The antimicrobial activity of the obtained extracts was evaluated using the agar diffusion method towards two Gram-positive pathogenic bacteria (Staphylococcus aureus and Staphylococcus epidermidis) and two Gram-negative bacteria (Pseudomonas aeruginosa and Escherichia coli). The extracts were tested at concentrations of 200, 500, 700, 800, 900 and 1000 µg.mL-1. The antimicrobial test showed that two (COA 009 and 014) of the 29 extracts inhibited bacterial growth of at least one of the strains each, from both Gram-positive and Gram-negative bacteria. The extracts with the inhibitory activity were derived from the fungi Curvularia sp. (COA 009) and Diaporthe sp. (COA 014).

Keywords: Gram-positive and Gram-negative bacteria, microorganisms, Loranthaceae.