Evaluation of natural compounds derived from plants on planktonic and sessile form of staphylococci

Abstract number: P1818

Avanzolini C., Cellini A., Papa R., Scoarughi G.L., Bombardelli E., Morazzoni P., Artini M., Selan L.

Objective: In this study the activity of different compounds of natural origin on planktonic and sessile cultures of S. aureus and S. epidermidis was tested. We used: i) a synthetic derivative of the dihydroxybenzofuran (DHBF), originally isolated from Krameria lappacea; ii) two quaternary benzo[c]phenanthridine alkaloids (QBAs), sanguinarine (SA) and chelerythrine (CH), extracted from Papaveraceae and Fumariaceae; iii) proanthocyanidin (proAC) and a standardised extract prepared from Vaccinium myrtillus L (BB).

Methods:S. aureus 6538P and S. epidermidis RP62A strains were used, reference strains for the biofilm formation. Determination of MIC and MBC for all natural compounds used was carried out. The influence on biofilm formation was assessed by a modified Christensen technique. The effect of the tested compounds on surface proteins and autolysins of the studied strains was evaluated by SDS-PAGE and zymogram, respectively. Surface proteins were extracted from bacteria cultured in the absence and in the presence of sub-inhibiting concentration of each compound.

Results: In planktonic cultures, both proAC and BB do not show an antibacterial activity in the range of used concentration, while DHBF and both QBAs show a clear bacteriostatic and/or bactericidal activity on the two tested strains. Interestingly, inhibition of biofilm formation was observed for all tested compounds, including proAC and BB. Moreover, DHBF, proAC and SA reduced S. epidermidis preformed biofilm despite the active concentration required are quite high. SDS-PAGE and zymogram analyses revealed diverse modification of surface protein pattern for treated bacteria in comparison with that of untreated bacteria, depending on the specific molecule used. In particular, the protein pattern of DHBF-treated samples is similar to the untreated samples. Furthermore, the modification profile observed for each strain is similar for both polyphenols (proAC and BB) and QBAs.

Conclusion: Our data suggest that some of the analyzed compounds could be proposed as antibacterial drugs in infection sustained by Staphylococcus spp. Their action on sessile phenotype renders them particularly interesting for a possible application in biofilm infections in synergic therapy.