Objective: To investigate antimicrobial activities of methanolic extract of leaves of Cleistocalyx operculatus L. (C. operculatus) grown in Vietnam. Methods: The methanolic extract of C. operculatus leaves was phytochemically screened and tested for its antimicrobial activity against six Gram-positive bacteria (three of which were antibiotic multiresistant Staphylococcus spp.), two Gram-negative bacteria, and one fungal species using an agar diffusion method. Anticaries activity was tested using pH drop and biofilm assays formed in 96-well plastic plates. Results: Phytochemical screening revealed the presence of flavonoids and terpenes, in which flavonoid content was 6.8 mg/g dry material. Antibacterial activity of the C. operculatus extract was shown only against Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis and Streptococcus mutans GS-5 (S. mutans), and three multiresistant bacteria being Staphylococcus epidermidis 847, Staphylococcus haemolyticus 535 and Staphylococcus aureus North German epidemic strain. Interestingly, methanolic extract of C. operculatus leaves exhibited the anticaries activity against S. mutans in terms of inhibition of acid production and biofilm formation. Activity of two key enzymes responsible for acidogenicity of S. mutans, F-ATPase and phosphotransferase system were inhibited by the extract with IC50 of 51.0 and 98.0 mg/mL, respectively. Cytotoxicity of the extract against keratinocytes was found only for higher concentrations [IC50=(119.98 ± 4.63) mg/mL]. Conclusions: The methanolic extract of C. operculatus leaves has the potential for development of antimicrobial preparations, especially anticaries products.

Objective To investigate antimicrobial activities of methanolic extract of leaves of Cleistocalyx operculatus L. (C. operculatus) grown in Vietnam. Methods The methanolic extract of C. operculatus leaves was phytochemically screened and tested for its antimicrobial activity against six Gram-positive bacteria (three of which were antibiotic multiresistant Staphylococcus spp.), two Gram-negative bacteria, and one fungal species using an agar diffusion method. Anticaries activity was tested using pH drop and biofilm assays formed in 96-well plastic plates. Results Phytochemical screening revealed the presence of flavonoids and terpenes, in which flavonoid content was 6.8 mg/g dry material. Antibacterial activity of the C. operculatus extract was shown only against Gram-positive bacteria Staphylococcus aureus, Bacillus subtilis and Streptococcus mutans GS-5 (S. mutans), and three multiresistant bacteria being Staphylococcus epidermidis 847, Staphylococcus haemolyticus 535 and Staphylococcus aureus North German epidemic strain. Interestingly, methanolic extract of C. operculatus leaves exhibited the anticaries activity against S. mutans in terms of inhibition of acid production and biofilm formation. Activity of two key enzymes responsible for acidogenicity of S. mutans, F-ATPase and phosphotransferase system were inhibited by the extract with IC

Objective To isolate α-mangostin (AMG) from the peels of mangosteen (Garcinia mangostana L.), grown in Vietnam, and to investigate antibiofilm activity of this compound against three Staphylococcus aureus (S. aureus) strains, one of which was methicillin-resistant S. aureus (MRSA) and the other two strains were methicillin-sensitive S. aureus (MSSA). Methods AMG in n-hexane fraction was isolated on a silica gel column and chemically analyzed by HPLC and NMR. The antibiofilm activity of this compound was investigated by using a 96-well plate model for the formation of biofilms. Biofilm biomass was quantified using crystal violet. The viability of cells was observed under confocal microscopy using LIVE/DEAD BacLight stains. Biofilm composition was determined using specific chemical and enzyme tests for polysaccharide, protein and DNA. Membrane-damaging activity was assayed by measuring the hemolysis of human red blood cells in presence of AMG. Results The results indicated that the isolated AMG, with a purity that exceeded 98%, had minimal inhibitory concentrations in the range of 4.6–9.2 μmol/L for the three strains tested. Interestingly, the MSSA strains were more sensitive to AMG than the MRSA strain. Minimal bactericidal concentrations were 2-fold higher than the minimal inhibitory concentration values for the three strains, indicating that AMG was a bactericidal compound. AMG also prevented biofilm formation effectively, albeit that again the MRSA strain was the most resistant. Interestingly, biofilms of the MRSA strain contained protein as a main component of the extracellular matrix, whereas this was polysaccharide in the MSSA strains. This might relate to the resistance of the MRSA 252 strain to AMG. Assays using human red blood cells indicated that AMG caused significant membrane damage with 50% of cell lysis occurred at concentration of about 36 μmol/L. Conclusions Our results provide evidence that the isolated AMG has inhibitory activity against biofilm formation by S. aureus, including MRSA. Thus, isolated AMG proposes a high potential to develop a novel phytopharmaceutical for the treatment of MRSA.