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Tectorigenin (TTR) is an O-methylated isoflavone derived from the rhizome ofBelamacanda chinensis(L.) DC. It is known to perform a wide spectrum of biological activities such as antioxidant, anti-inflammatory, anti-tumor. The aim of this study is to examine the mechanism of antibacterial activity of TTR against methicillin-resistantStaphylococcus aureus(MRSA). The anti-MRSA activity of TTR was analyzed in combination assays with detergent, ATPase inhibitors, and peptidoglycan (PGN) derived fromS. aureus. Transmission electron microscopy (TEM) was used to monitor survival characteristics and changes inS. aureusmorphology. The MIC values of TTR against all the tested strains were 125 μg/mL. The OD(600) of each suspension treated with a combination of Triton X-100, DCCD, and NaN3with TTR (1/10 × MIC) had been reduced from 68% to 80%, compared to the TTR alone. At a concentration of 125 μg/mL, PGN blocked antibacterial activity of TTR. This study indicates that anti-MRSA action of TTR is closely related to cytoplasmic membrane permeability and ABC transporter, and PGN at 125 μg/mL directly bind to and inhibit TTR at 62.5 μg/mL. These results can be important indication in study on antimicrobial activity mechanism against multidrug resistant strains.

Punica granatumis commonly used in Korea as a traditional medicine for the treatment of pathogenic bacteria. In this study, we investigated thein vitroandin vivoantimicrobial activity ofP. granatumpeel EtOH extract (PGPE) against 16 strains ofSalmonella. The minimal inhibitory concentrations of PGPE were in the range of 62.5–1000 x03BCg mL-1. In addition, thein vivoantibacterial activity of the PGPE extract was examined in aS. typhimuriuminfection mouse model. Mice were initially infected withS. typhimuriumand then with PGPE. The extract was found to have significant effects on mortality and the numbers of viableS. typhimuriumrecovered from feces. Although clinical signs and histological damage were rarely observed in the treated mice, the untreated controls showed signs of lethargy and histological damage in the liver and spleen. Taken together, the results of this study indicate that PGPE has the potential to provide an effective treatment for salmonellosis.

Shikonin (SKN), a highly liposoluble naphthoquinone pigment isolated from the roots ofLithospermum erythrorhizon, is known to exert antibacterial, wound-healing, anti-inflammatory, antithrombotic, and antitumor effects. The aim of this study was to examine SKN antibacterial activity against methicillin-resistantStaphylococcus aureus(MRSA). The SKN was analyzed in combination with membrane-permeabilizing agents Tris and Triton X-100, ATPase inhibitors sodium azide andN,N′-dicyclohexylcarbodiimide, andS. aureus-derived peptidoglycan; the effects on MRSA viability were evaluated by the broth microdilution method, time-kill test, and transmission electron microscopy. Addition of membrane-permeabilizing agents or ATPase inhibitors together with a low dose of SKN potentiated SKN anti-MRSA activity, as evidenced by the reduction of MRSA cell density by 75% compared to that observed when SKN was used alone; in contrast, addition of peptidoglycan blocked the antibacterial activity of SKN. The results indicate that the anti-MRSA effect of SKN is associated with its affinity to peptidoglycan, the permeability of the cytoplasmic membrane, and the activity of ATP-binding cassette (ABC) transporters. This study revealed the potential of SKN as an effective natural antibiotic and of its possible use to substantially reduce the use of existing antibiotic may also be important for understanding the mechanism underlying the antibacterial activity of natural compounds.