Effects of Rhodomyrtus tomentosa extract on virulence factors of Candida albicans and human neutrophil function.

OBJECTIVE: Candida albicans has become a major problem of oral candidiasis due to increase in antibiotic resistance. 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 anti-virulence and immunostimulatory activity of R. tomentosa ethanolic leaf extract against C. albicans. METHODS: The effects of the extract on C. albicans were assessed on germ tube production, adherence of the organisms to surfaces, and biofilm. In addition, the effects of the extract on phagocytosis and killing activity of neutrophils against the pathogen were investigated. RESULTS: Suppression of germ tube production following 30 min exposure to the extract at 256 µg/mL was significantly increased in comparison with that of the unexposed cells (p < 0.05). The pathogens demonstrated a significant reduction in adherence ability to surfaces in a dose dependent manner, compared with the control (p < 0.05). At 48 h, the extract at 512-1024 µg/mL significantly reduced biofilm forming ability of the organisms up to 42.31-64.58% (p < 0.05). Compared with the control group, a significant inhibition of mature biofilm after treated with the extract at 256 µg/mL was observed (p < 0.05). The extract at 50 µg/mL significantly enhanced phagocytosis and killing activity of neutrophils against the organism, compared with the control (p < 0.05). CONCLUSIONS: The findings suggest that R. tomentosa extract displayed a dual mode of action, inhibiting virulence factors of C. albicans and enhancing neutrophil functions. Further pharmaceutical development of the extract might be useful as an alternative therapeutic agent against oral candidiasis.

Effects of Rhodomyrtus tomentosa Extract on Killing Activity of Human Neutrophils and Membrane Integrity of Enterohaemorrhagic Escherichia coli O157:H7.

Enterohaemorrhagic Escherichia coli (E. coli) O157:H7 is one of the most virulent causative agents of foodborne disease. Use of antibiotics for the treatment against E. coli O157:H7 infection leads to hemolytic uremic syndrome. The present study evaluated the potential of ethanolic leaf extract of a medicinal plant, Rhodomyrtus tomentosa in enhancing the killing activity of human neutrophils against E. coli O157:H7. In addition, the effects of the extract on membrane permeability of the organisms were studied. In the killing assay, percentage survival of the bacterial cells after being exposed to human neutrophils in the presence of various concentrations of the extract were determined. At 45 min, percentage survival of E. coli O157:H7 and E. coli ATCC 25922 after treated with neutrophils in the presence of the extract at 125-250 µg/mL was 58.48%-50.28% and 69.13%-35.35%, respectively. Furthermore, upon treatment with R. tomentosa at 250 µg/mL uptake of crystal violet by E. coli O157:H7 and E. coli ATCC 25922 was increased to 40.07% and 36.16%, respectively. Therefore, it is suggested that the extract exhibited dual effects as immunostimulant and membrane permeabilizing agent perhaps resulted in enhancing the killing activity of neutrophils against the organisms.