Abstract
Staphylococci growing in the form of biofilm exhibit high resistance to a plethora of antibiotics. The aim of the study was to assess the influence of ethanolic extract of propolis (EEPs) on S. epidermidis ATCC 35984 biofilm using fluorescent microscopy. Propidium iodide (PI) and SYTO 9 were used for differentiation of live and dead cells, and calcofluor white was used to stain the extracellular matrix, the self-produced extracellular polymeric substances (EPS). The outcomes of the research confirm the promising potential of EEPs for eradication of staphylococcal biofilm. However, its activity cannot be classified as fully satisfactory, either in terms of the effectiveness of elimination of bacterial cells or disturbing the EPS structure. A two or even four times higher concentration of EEPs compared to MIC (Minimum Inhibitory Concentration) against planktonic cells (128 µg/mL) was necessary for effective (estimated for 90%) elimination of living cells from the biofilm structure. Unfortunately, even at that concentration of EEPs, the extracellular matrix was only partially disturbed and effectively protected the residual population of living cells of S. epidermidis ATCC 35984. In our opinion, a combination of EEPs with agents disrupting components of EPS, e.g., proteases, lysines, or enzymes degrading extracellular DNA or PIA (polysaccharide intercellular adhesin).
Highlights
Bacteria of the genus Staphylococcus, S. aureus and S. epidermidis, belong to the most common and most dangerous human and animals’ pathogens
The selection of the propolis sample for microscopic studies was based on the outcomes of two preliminary assays: determination of total phenolic content and determination of Minimum Inhibitory Concentration (MIC) values against planktonic cells of selected strains of staphylococci, which were performed according to procedures presented in our previous report [19]
The investigation of Williams and Bloebaum indicated that, after 48 h of growth, the S. epidermidis ATCC 35984 produced a mature biofilm with a significant network of matrix components and found this strain useful for microscopic studies of staphylococcal biofilms [20]
Summary
Bacteria of the genus Staphylococcus, S. aureus and S. epidermidis, belong to the most common and most dangerous human and animals’ pathogens They produce a broad range of virulence factors, are common in the environment, and evolve and acquire resistance to a plethora of antibiotics [1,2,3,4]. Another important feature of these bacteria, both in terms of the frequency of infection and the effectiveness of their treatment, is their ability to grow in the form of biofilm, a community of cells that are embedded in a matrix of self-produced extracellular polymeric substances (EPS) [4,5,6]. This has been proven for both S. aureus and S. epidermidis [7,8]
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