Different antibacterial actions of isoflavones isolated from Erythrina poeppigiana against methicillin-resistant Staphylococcus aureus.
OBJECTIVE
To screen six isoflavones isolated from Erythrina poeppigiana (Leguminosae) for their antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA).


RESULTS
Stem bark of E. poeppigiana was macerated with acetone and the methylene chloride-soluble fraction of the residue was applied to repeated silica gel column chromatography and eluted. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) were determined by a broth dilution method. Inactive compounds that failed inhibiting bacterial growth at 25 microg ml(-1) were further investigated for their combination effects with methicillin and oxacillin. Of the isolated isoflavones, 5,7,4'-trihydroxy-8,3'-di(gamma,gamma-dimethylallyl)isoflavone (isolupalbigenin) exhibited the highest anti-MRSA activity (MICs: 1.56-3.13 microg ml(-1); MBCs: 6.25-12.5 microg ml(-1)), followed by 5,7,4'-trihydroxy-6-gamma,gamma-dimethylallylisoflavone (erythrinin B). Inactive compounds were combined with methicillin or oxacillin, 5,4'-dihydroxy-(3'',4''-dihydro-3''-hydroxy)-2'',2''-dimethylpyrano[5'',6'':6,7]isoflavone (M-Wi-2) intensifying the susceptibility of MRSA strains to these antibiotics. In all but one strain, the MIC values of methicillin were reduced from > or =100 to 6.25-12.5 microg ml(-1) in the presence of M-Wi-2 (25 microg ml(-1)).


CONCLUSIONS
Isoflavones from E. poeppigiana showed two different antibacterial activities against MRSA: direct growth inhibition and intensification of methicillin sensitivity.


CONCLUSIONS
Isolupalbigenin and M-Wi-2 could lead to the development of compounds for new approaches against MRSA infection.
Sato
M
M
Department of Oral Pathology, Asahi University School of Dentistry, Gifu, Japan. patho@dent.asahi-u.ac.jp
Tanaka
H
H
Tani
N
N
Nagayama
M
M
Yamaguchi
R
R
D000096:Acetone / Q000737:chemistry; D000900:Anti-Bacterial Agents / Q000302:isolation & purification / Q000494:pharmacology*; D004895:Erythrina / Q000737:chemistry*; D007529:Isoflavones / Q000302:isolation & purification / Q000494:pharmacology*; D008712:Methicillin / Q000494:pharmacology; D016106:Methicillin Resistance / Q000187:drug effects*; D024301:Plant Bark / Q000737:chemistry; D013211:Staphylococcus aureus / Q000187:drug effects*
D000900:Anti-Bacterial Agents; D007529:Isoflavones; D000096:Acetone; D008712:Methicillin