Abstract

Asplenium serratum L. (Aspleniaceae) is a terrestrial, epiphytic or humicole fern used as traditional medicine in different countries to treat infection. As such, this study aimed to assess the antibacterial potential of a crude ethanol extract from A. serratum leaves against multidrug-resistant bacteria from a hospital setting. Fern leaves were dried and ground using 96° Gay Lussac ethanol, with the extract concentrated in a rotary evaporator. Eleven bacterial strains were tested, including gram-positive (Enterococcus faecalis 1, Staphylococcus aureus, methicillin-sensitive S. aureus, S. aureus 8380, S. aureus ATCC 25923, Staphylococcus epidermidis) and gram-negative bacteria (Proteus mirabilis 464, Pseudomonas aeruginosa 36408, Enterobacter cloaceae 406, Klebsiella pneumoniae 6891, Escherichia coli 635). The disk agar diffusion test was used to assess the antimicrobial activity of the extracts. Disks of filter paper (5 mm wide) were prepared, each containing 5 µl of different plant extract concentrations (5, 10, 15, 20, 30, 40 and 50 mg.ml-1, using dimethyl sulfoxide - DMSO -  as solvent). The antibiotic oxacillin (1 mg) was used as a positive control and disks containing DMSO only as negative control. The Petri dishes and disks were incubated for 24 h (36.5-37°C), after which the formation of zones of inhibition was measured. The tests were performed in duplicates. After incubation, all the positive control (oxacillin) disks contained zones of inhibition of bacterial growth, while none were observed for negative controls or the disks containing different concentrations of A. serratum extract. Ethanol extracts of A. serratum leaves showed no antibiotic activity against the microorganisms tested, precluding confirming the popular belief of anti-infective properties for this fern species for multidrug-resistant bacteria.

Key words: Aspleniaceae, multidrug-resistant bacteria, ethnobotany, medicinal plants, ferns.