Comparative study on the antibacterial activity of some flavonoids and their sulfonic derivatives

The antibacterial activity of quercetin, morin, sodium salt of quercetin-5'-sulfonic acid (NaQSA) and sodium salt of morin-5'-sulfonic acid (NaMSA) were tested against six bacterial strains: Escherichia coli (ATCC 25922 and clinical isolates--ESBL), Pseudomonas aeruginosa (ATCC 27853 and clinical isolates--carbapenem resistant), Staphylococcus aureus (ATCC 29213 and clinical isolats- MRSA). The most effective inhibitors against the model strain S. aureus are NaQSA and NaMSA (MIC = 3.9 microg/mL). Among polyhydroxyflavones used in this investigation, morin exhibits the highest antibacterial activity against tested strains. The structure-activity relationship indicates that 2',4'-dihydroxylation of the B ring in the flavanone structure is important for significant antibacterial activity and that substitution of the sulfo group at position 5' on the lateral phenyl ring enhances antistaphylococcal activity of flavonoids.