Effects of Rhodomyrtus tomentosa (Aiton) Hassk. Leaf Extract on Human Neutro

Abstract

Rhodomyrtus tomentosa (Aiton) Hassk is the source of an ethanolic extract. The principal compounds of these products are bioactive substances extracted from the plant that are known to possess antioxidant, antibacterial, anti-inflammatory, and immunomodulatory properties. Enterohemorrhagic Escherichia coli (E. coli) O157:H7 is one of the most virulent causative agents of foodborne disease. Use of antibiotics in the treatment of E. coli O157:H7 infection leads to hemolytic uremic syndrome. The present study evaluated the potential of the ethanolic leaf extract of the medicinal plant, Rhodomyrtus tomentosa extract to enhance the killing activity of human neutrophils against E. coli O157:H7. In addition, the effects of the extract on the membrane permeability of the organism were studied. The percentage survival of the bacterial cells after exposure to human neutrophils, in the presence of various concentrations of the extract, was determined by a killing assay. At 45 min, after exposure to neutrophils in the presence of the extract at concentrations of 125 to 250 μg/mL, the percentage survivals of E. coli O157:H7 and E. coli ATCC 25922 were 58.48% to 50.28% and 69.13% to 35.35%, respectively. Furthermore, upon treatment with R. tomentosa at 250 μg/mL, the uptake of crystal violet by E. coli O157:H7 and E. coli ATCC 25922 increased to 40.07% and 36.16%, respectively. Oral candidiasis has become a major problem due to the increasing resistance of Candida albicans to antibiotics. Rhodomyrtus tomentosa, a medicinal plant possessing several phytochemical constituents, has been considered as a potential source of antimicrobial and immunomodulatory agents. The aim of this study was to investigate the anti-virulence and immunostimulatory activities of R. tomentosa ethanolic leaf extract against C. albicans. The effects of the extract on C. albicans were assessed on germ tube production, adherence of the organisms to surfaces, biofilm formation, and mature biofilm. In addition, the effects of the extract on phagocytosis and the killing activity of neutrophils against the pathogen were investigated. Suppression of germ tube production following exposure to the extract at 256 μg/mL significantly increased in comparison with that of the unexposed cells (p < 0.05). The pathogens demonstrated a significantly reduced ability to adhere to surfaces in a dose dependent manner, compared with the control (p < 0.05). At 48 h, the extract at 512 to 1024 μg/mL had reduced the ability of the organism to form biofilm by up to 42.31 to 64.58% (p < 0.05). Compared with the control group, there was a significantly increased inhibition of mature biofilm after treatment with the extract at 256 μg/mL (p < 0.05). The extract at 50 μg/mL significantly enhanced phagocytosis and the killing activity of neutrophils against the organism, compared with the control (p < 0.05). R. tomentosa extract displayed a specific mode of action as a membrane permeabilizing agent, inhibiting the virulence factors of C. albicans, and enhancing the killing activity of neutrophils against the organism. Further development of the extract as an alternative therapy for oral candidiasis might be useful.