Surasak Limsuwan

Rhodomyrtone: A new candidate as natural antibacterial drug from Rhodomyrtus tomentosa

Rhodomyrtone [6,8-dihydroxy-2,2,4,4-tetramethyl-7-(3-methyl-1-oxobutyl)-9-(2-methylpropyl)-4,9-dihydro-1H-xanthene-1,3(2H)-di-one] from Rhodomyrtus tomentosa (Aiton) Hassk. displayed significant antibacterial activities against gram-positive bacteria including Bacillus cereus, Bacillus subtilis, Enterococcus faecalis, Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Staphylococcus epidermidis, Streptococcus gordonii, Streptococcus mutans, Streptococcus pneumoniae, Streptococcus pyogenes, and Streptococcus salivarius. Especially noteworthy was the activity against MRSA with a minimum inhibitory concentration (MIC) and a minimum bactericidal concentration (MBC) ranging from 0.39 to 0.78 microg/ml. As shown for S. pyogenes, no surviving cells were detected within 5 and 6h after treatment with the compound at 8MBC and 4MBC concentrations, respectively. Rhodomyrtone displays no bacteriolytic activity, as determined by measurement of the optical density at 620 nm. A rhodomyrtone killing test with S. mutans using phase contrast microscopy showed that this compound caused a few morphological changes as the treated cells were slightly changed in color and bigger than the control when they were killed. Taken together, the results support the view that rhodomyrtone has a strong bactericidal activity on gram-positive bacteria, including major pathogens.

Boesenbergia pandurata (Roxb.) Schltr., Eleutherine americana Merr. and Rhodomyrtus tomentosa (Aiton) Hassk. as antibiofilm producing and antiquorum sensing in Streptococcus pyogenes

Biofilm formation has been demonstrated as a potentially important mechanism contributing to antibiotic treatment failure on Streptococcus pyogenes. It could play a significant role in recurrent and chronic infections. Boesenbergia pandurata (Roxb.) Schltr., Eleutherine americana Merr. and Rhodomyrtus tomentosa (Aiton) Hassk. have been previously reported from our laboratory as effective agents against S. pyogenes. Therefore, in the present study, we observed the effect of these plants on biofilm formation. The bacterial biofilms were quantified by safranin staining and absorbance at 492 nm. The results clearly demonstrated that all subinhibitory concentrations [1/32-1/2 minimal inhibitory concentration (MIC)] of E. americana (7.81-125 microg mL(-1)) and R. tomentosa (0.24-7.81 microg mL(-1)) extracts significantly prevented biofilm formation while 1/2MIC (7.81 microg mL(-1)) of B. pandurata extract produced this effect. The issue of antiquorum sensing of this pathogenic bacterium has been further explored. A correlation between antiquorum-sensing and antibiofilm-producing activities was demonstrated. Strong inhibition on quorum sensing was displayed with the extract of R. tomentosa. Eleutherine americana extract showed partial inhibition, while B. pandurata did not show this activity. By contrast, an assay of microbial adhesion to hydrocarbon revealed no changes in the cell-surface hydrophobicity of the treated organisms. Active organisms with the ability to inhibit quorum sensing and biofilm formation are worth studying as they may provide complimentary medicine for biofilm-associated infections.

Medicinal Plant Extracts as Anti-Escherichia coli O157:H7 Agents and Their Effects on Bacterial Cell Aggregation

Ethanolic extracts of eight Thai medicinal plants (representing five families) that are used as traditional remedies for treating diarrhea were examined with a salt aggregation test for their ability to modulate cell surface hydrophobicity of enterohemorrhagic Escherichia coli strains, including E. coli O157:H7. Four of these medicinal plants, Acacia catechu, Peltophorum pterocarpum, Punica granatum, and Quercus infectoria, have high bacteriostatic and bactericidal activities. The ethanolic extract of Q. infectoria was the most effective against all strains of E. coli, with MICs of 0.12 to 0.98 mg/ml and MBCs of 0.98 to 3.91 mg/ml. The ethanolic extract of P. granatum had MICs of 0.49 to 1.95 mg/ml and MBCs of 1.95 to 3.91 mg/ml. Ethanolic extracts of Q. infectoria, P. pterocarpum, and P. granatum were among the most effective extracts against the two strains of E. coli O157:H7. The other four plants, Andrographis paniculata, Pluchia indica, Tamarindus indica, and Walsura robusta, did not have high bacteriostatic and bactericidal activities but were able to affect hydrophobicity characteristics on their outermost surface. All plants except Q. infectoria had some ability to increase cell surface hydrophobicity. There appears to be no correlation between antibacterial activity and cell aggregative properties.

Potential antibiotic and anti-infective effects of rhodomyrtone from Rhodomyrtus tomentosa (Aiton) Hassk. on Streptococcus pyogenes as revealed by proteomics.

Rhodomyrtone from Rhodomyrtus tomentosa (Aiton) Hassk. leaf extract has a strong antibacterial activity against the bacterial pathogen Streptococcus pyogenes. Our previous studies indicated that the bactericidal activity of rhodomyrtone might involve intracellular targets. In the present studies we followed a proteomics approach to investigate the mode of action of rhodomyrtone on S. pyogenes. For this purpose, S. pyogenes was cultivated in the presence of 0.39 μg/ml rhodomyrtone, which corresponds to 50% of the minimal inhibitory concentration. The results show that the amounts of various enzymes associated with important metabolic pathways were strongly affected, which is consistent with the growth-inhibiting effect of rhodomyrtone. Additionally, cells of S. pyogenes grown in the presence of rhodomyrtone produced reduced amounts of known virulence factors, such as the glyceraldehyde-3-phosphate dehydrogenase, the CAMP factor, and the streptococcal pyrogenic exotoxin C. Taken together, these findings indicate that rhodomyrtone has both antimicrobial and anti-infective activities, which make it an interesting candidate drug.

Medicinal plants with significant activity against important pathogenic bacteria

Interest in the study of medicinal plants as a source of pharmacologically active compounds has increased worldwide. This study is a broad screening of 31 plant species against a wide range of pathogenic bacteria, including Acinetobacter baumannii, Bacillus cereus, Enterococcus faecalis, Escherichia coli, Klebsiella pneumoniae, Listeria monocytogenes, Pseudomonas aeruginosa, Salmonella spp., Shigella flexneri, Staphylococcus aureus, Streptococcus mutans, and Streptococcus pyogenes. The agar disk diffusion method showed that most plants were more active against gram-positive than gram-negative bacteria. Streptococcus pyogenes was the most sensitive organism inhibited by nearly all of the extracts (97.6%), followed by Bacillus cereus (63.4%) and Staphylococcus aureus (61.0%). The ethanol extracts of Rhodomyrtus tomentosa (Aiton) Hassk. (Myrtaceae) (leaf) and Eleuterine americana Merr. (bulb) exhibited good antibacterial activity against gram-positive bacteria. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of Rhodomyrtus tomentosa ranged from 3.9 to 7.8 and 7.8 to 125 μg/mL, respectively, while those of Eleuterine americana were 120–125 and 250–1000 μg/mL, respectively. Quercus infectoria G. Olivier (Fagaceae) and Piper betle L. (Piperaceae) showed a broad spectrum of activity. The ethanol extract from the nut galls of Quercus infectoria demonstrated significant activity against all important pathogens. It inhibited the growth of all pathogens, with MIC values of 62.5–1000 μg/mL. The MBC ranged from 125 to 1000 μg/mL in most species, except Enterococcus faecalis. The ethanol extract from Piper betle (leaves) demonstrated antibacterial activity against almost all species with the same MIC and MBC values, ranging from 125 to 500 μg/mL.

A new flavellagic acid derivative and phloroglucinol from Rhodomyrtus tomentosa

A new flavellagic acid derivative, 3,3′,4,4′-tetra-O-methylflavellagic acid and six known compounds were isolated from the stems of Rhodomyrtus tomentosa while a new phloroglucinol, named rhodomyrtosone I, and six known compounds were isolated from the fruit. Their structures were elucidated by spectroscopic analyses as well as by comparisons with related compounds.

Antibacterial Activity of Rhodomyrtus tomentosa (Aiton) Hassk. Leaf Extract against Clinical Isolates of Streptococcus pyogenes.

Ethanol extract of Rhodomyrtus tomentosa (Aiton) Hassk. leaf was evaluated for antibacterial activity against 47 clinical isolates of Streptococcus pyogenes. The extract exhibited good anti-S. pyogenes activity against all the tested isolates with similar minimum inhibitory concentration (MIC, 3.91–62.5 μg mL−1) and minimum bactericidal concentration (MBC, 3.91–62.5 μg mL−1) ranges. No surviving cells were detected at 16 h after treatment with 8 × MIC of the extract. The extract-treated cells demonstrated no lysis and cytoplasmic leakage through the bacterial membrane. Electron micrographs further revealed that the extract did not cause any dramatic changes on the treated cells. Rhodomyrtone, an isolated compound, exhibited good anti-S. pyogenes activity (14 isolates), expressed very low MIC (0.39–1.56 μg mL−1) and MBC (0.39-1.56 μg mL−1) values. Rhodomyrtus tomentosa leaf extract and rhodomyrtone displayed promising antibacterial activity against clinical isolates of S. pyogenes.

Thai Herbal Formulas Used for Wound Treatment: A Study of Their Antibacterial Potency, Anti-Inflammatory, Antioxidant, and Cytotoxicity Effects

AIM This present work was aimed to investigate wound healing-related biologic activities of traditional herbal formulas used for wound treatment in southern Thailand. METHODS Water and ethanol extracts of the formulas (THR-SK004, THR-SK010, and THR-SK011) were tested for their antibacterial potency against methicillin-resistant Staphylococcus aureus (MRSA) and -susceptible S. aureus. Anti-inflammatory activities of the extracts were assessed by detection of the inhibition of lipopolysaccharide-induced nitric oxide production. Anti-oxidant activities and cytotoxicity of the extracts were also measured. RESULTS Among the tested formulas, ethanol extract of THR-SK010 consisting of four herbs: Curcuma longa L., Areca catechu L., Oryza sativa L., and Garcinia mangostana L., was found to possess promising antibacterial activities with MIC90 of 4 μg mL(-1) against MRSA isolates. This ethanol extract offered the highest anti-inflammatory activity as well as DPPH and hydroxyl radical scavenging activities. CONCLUSIONS Remarkable antibacterial, anti-inflammatory, and antioxidant activities as well as low toxicity on Vero cells of THR-SK010 ethanol extract provide scientific information to support the topical use of the formula for wound treatment. This information proposes the potential to develop a new generation of phytopharmaceuticals based on traditional knowledge.

Inhibition of microbial adhesion to plastic surface and human buccal epithelial cells by Rhodomyrtus tomentosa leaf extract.

OBJECTIVE The adherence of oral pathogenic microorganisms to host tissues is the initial step for successful process of oral diseases. This study aimed to determine the effect of the Rhodomyrtus tomentosa leaf extract and rhodomyrtone, an antibacterial compound from R. tomentosa leaf, on adhesion of some oral pathogens to polystyrene plastic surface and human buccal epithelial cells. METHODS The minimum inhibitory concentration (MIC) was evaluated using broth microdilution method. The microbial adhesion to the plastic surface and buccal cells was determined using microtiter plate method and microscopy technique. RESULTS The ethanol extract of leaf demonstrated antibacterial activity against oral microorganisms including Staphylococcus aureus ATCC 25923, Streptococcus mutans (clinical isolate), and Candida albicans ATCC 90028 with the MIC values of 31.25, 15.62, and 1000μg/ml, respectively. Rhodomyrtone displayed activity with the MIC values of 0.78 and 0.39μg/ml against S. aureus ATCC 25923 and S. mutans, respectively. The MIC value of the compound against C. albicans ATCC 90028 was more than 100μg/ml which was the highest test concentration. All pathogenic microorganisms treated with the extract and rhodomyrtone at their subinhibitory concentrations resulted in a decrease in their adherence ability to both plastic surface and buccal cells. CONCLUSION It is suggested that R. tomentosa extract and rhodomyrtone may be useful in therapy or as prophylaxis in infections involving oral pathogens.

Chemical constituents and antimicrobial properties of the essential oil and ethanol extract from the stem of Aglaia odorata Lour.

The stem-derived essential oil of Aglaia odorata Lour. was obtained by hydrodistillation using a Clevenger-type system. Gas chromatography–mass spectrometry analysis of the oil revealed the identification of 39 compounds, representing 76.4% of the oil; germacrene D (20.3%), α-humulene (17.1%), α-himachalene (12.7%) and β-caryophyllene (10.2%) were the major components. Ar-turmerone (1) and eichlerialactone (2) were isolated from the stem oil and ethanolic stem extract of this plant species, respectively. Antimicrobial activities of the oil and ethanol extract were tested against both Gram-positive and Gram-negative bacterial strains including Bacillus cereus ATCC 11778, Staphylococcus aureus ATCC 25923, Acinetobacter baumannii ATCC 19606 and Escherichia coli ATCC 25922, as well as three rice fungal pathogens Bipolaris oryzae, Pyricularia oryzae and Rhizoctonia solani using broth microdilution method. The oil and 1 exhibited significant antifungal activity against the three rice pathogens tested, whereas 2 exhibited good antibacterial activity against both the Gram-positive pathogens tested.