Synergism of flavonoids with bacteriostatic action against Staphylococcus aureus ATCC 25 923 and Escherichia coli ATCC 25 922

In our previous studies, bacteriostatic action of flavonoids against Staphylococcus aureus ATCC 25 923 and Escherichia coli ATCC 25 922 was demostrated. In the present work synergism of their combinations in order to improve the bacteriostatic action against the same microorganisms was determined. The experiences were made in nutritive broth, maintaining constant one drug concentration (20 µg/ml) and increasing the other one. A turbidimetric kinetic method was used and by means of a mechanism previously proposed, the minimal inhibitory concentrations (MIC's) of each flavonoid combination were determined. The MIC's for assayed combinations against S. aureus were: variable morin - constant rutin: 157.44 µg/ml and variable quercetin - constant morin: 29.9 µg/ml. The values obtained against E. coli were: variable morin - constant rutin: 78.5 µg/ml; variable quercetin -constant rutin: 47.4 µg/ml; variable quercetin - constant morin: 25 µg/ml; variable morin - constant quercetin: 27.4 µg/ml.

A comparative study of bacteriostatic activity of synthetic hydroxylated flavonoids

Among other properties, flavonoids present a notable bacteriostatic activity. In this paper, minimal inhibitory concentrations (MICs) of 5,7,4'-trihydroxyflavanone (naringenin), 5,7-dihydroxyflavone and 2',4',4- trihydroxychalcone (isoliquitirigenin) against Staphylococcus aureus ATCC 25 923 were determined and compared to values obtained for other chalcones and flavanones previously investigated. Specific growth rates and MICs were determined by a turbidimetric kinetic method. The observed sequence MICflavanone (inactive) >MIC7-hidroxyflavanone (197.6 µgml-1)>MIC5,7,4'-trihydroxyflavanone (120 µgml-1) showed that the introduction of an electron donating group (-OH) causes an increase in bioactivity. On the other hand, the comparisons MIC5,7,4'-trihydroxyflavanone (120 µgml-1) >>> MIC2',4',4-trihydroxychalcone (29 µgml-1) and MIC5,7-dihydroxyflavone (105 µgml-1) >>> MIC2',4'-dihydroxychalcone (28.8 µgml-1) indicated that the chalcone structure is the most favourable for bacteriostatic activity within the flavonoid family.

Structure-biological activity relationship of synthetic trihydroxilated chalcones

The bacteriostatic activity of 2',4',2'-trihydroxychalcone; 2',4',3'-trihydroxychalcone and 2',4',4'-trihydroxychalcone, prepared by condensation of 2,4-dihydroxyacetophenone and benzaldehyde substituted, against "Staphylococcus aureus" ATCC 25923 was assayed by agar plate method. The three compounds presented important inhibition halos. In order to elucidate structure-activity relationships, the minimal inhibitory concentrations against "S. aureus"were determined by the broth dilution method and the results obtained were compared to that of 2',4'-(OH)2>MIC 2',4',4'-(OH)3>>MIC 2',4',2-(OH)3. these results showed that the introduction of an electron donating group (-OH) in the aromatic B-ring causes an increase in bioactivity, and that the intensity of action depends on the position of the OH substitute.