Antistaphylococcal and biofilm inhibitory activities of Frangula alnus bark ethyl-acetate extract

•Frangula alnus bark extract was chemically characterized.•Antibiofilm effect of Frangula alnus bark extract on clinical isolates was detected.•The extract caused changes in bacterial respiration in planktonic/biofilm form.•Scanning electron microscopy confirmed the changes in biofilm structure. Staphylococcus aureus is one of the leading causative of numerous infections that is resistant to various antibiotics. Since that we are facing with a serious problem of bacterial resistance it is necessary to find a new antibacterial agents in fight with it. Frangula alnus is traditionally used plant but its antibiofilm potential is poorly investigated. The aim of the study was to investigate antibiofilm activity of F. alnus ethyl-acetate extract (FA) toward S. aureus ATCC strains and clinical isolates as well as its influence on respiration in planktonic and biofilm form. The qualitative GCxGC–MS and quantitative LC–MS/MS analysis revealed that FA extract was rich in phenols and flavonoids and emodin, chatechin, and ester 4-ethoxy benzoic acid were the most dominant components. Results obtained through microdillution assay showed that FA possesses strong antibacterial activity. Furthermore, crystal violet staining of biofilm biomass demonstrated that extract had strong effect on biofilm formation of all tested strains while effect on preformed biofilms was less pronounced. The effect on biofilm was confirmed with scanning electron microscopy where the changes in biofilm structure were noticed. The activity of extract on the consumption of O2 and production of CO2 was monitored using the Micro-Oxymax respirometer. Interestingly, respiration of the most strains was decreased in planktonic form as well as in biofilms. Results obtained in this study are a good basis for further research in order to discover the mechanism of action of the FA extract on connection between biofilm and respiration.