Anti-MRSA Activity of Oxysporone and Xylitol from the Endophytic Fungus Pestalotia sp. Growing on the Sundarbans Mangrove Plant Heritiera fomes

Heritiera fomes Buch.-Ham., a mangrove plant from the Sundarbans, has adapted to a
unique habitat, muddy saline water, anaerobic soil, brackish tidal activities and high
microbial competition. Endophytic fungal association protects this plant from adverse
environmental conditions. This plant is used in Bangladeshi folk medicine, but it has not
been extensively studied phytochemically, and there is hardly any report on investigation
on endophytic fungi growing on this plant. In this study, endophytic fungi were isolated
from the surface sterilized cladodes and leaves of H. fomes. The antimicrobial activities
were evaluated against two Gram-positive and two Gram-negative bacteria and the
fungal strain, Candida albicans. Extracts of Pestalotia sp. showed activities against all test
bacterial strains, except that the EtOAc extract was inactive against E. coli. The
structures of the purified compounds, oxysporone and xylitol, were elucidated by
spectroscopic means. The anti-MRSA potential of the isolated compounds were
determined against various MRSA strains, i.e., ATCC 25923, SA-1199B, RN4220, XU212,
EMRSA-15 and EMRSA-16, with MIC values ranging from 32-128 μg/mL. This paper,
for the first time, reports on the anti-MRSA property of oxysporone and xylitol, isolation
of the endophyte Pestalotia sp. from H. fomes, and isolation of xylitol from a Pestalotia sp.