Quercetin mediated inhibition of Staphylococcus aureus biofilms and the impact of the isolate phenotype and genotype

Abstract

Aim: This study was designed to assess the antibiofilm activity of quercetin on characterized S. aureus isolates. Methodology: This study evaluated 36 S. aureus isolates, each of which was identified using Gram staining, culture, biochemical, and PCR assays. Isolates were cultured and their biofilm production was evaluated using Congo red agar (CRA) plates, microtiter plate tests and PCR, and the effects of quercetin were examined. Results: The CRA results revealed that eight (22.3%) S. aureus isolates were strongly positive for biofilm production and an additional 18 isolates (50%) showed moderate biofilm capacity. The remaining 10 isolates were negative (27.7%) for biofilm production. S. aureus isolates were divided into strong positive, intermediate, and negative groups, 27.8%, 44.5%, and 27.7%, respectively. Scanning electron microscopy showed that the biofilm-producing isolates appeared as aggregates of cells within a heavy matrix. In addition, PCR assay identified IcaA and IcaD (66.6% for both) biofilm production genes in most isolates and IcaC (61.1%), IcaB, FnbB (33.3% for both), and Fib (22.2%) in several other strains. Quercetin significantly inhibited biofilm activity in biofilm producing S. aureus isolates in a dose-dependent manner, with an inhibition rate of 29.6-87.7%. Interpretation: Biofilm production is dependent on Ica gene phenotype and strains with an IcaABCD or IcaABD phenotype produce more biofilm than strains with IcaAD phenotype. Quercetin significantly inhibited S. aureus biofilm production, irrespective of Ica phenotype.