Use of non-thermal plasma pre-treatment to enhance antibiotic action against mature Pseudomonas aeruginosa biofilms.

Non-thermal plasma (NTP), generated at atmospheric pressure by DC cometary discharge with a metallic grid, and antibiotics (gentamicin-GTM, ceftazidime-CFZ and polymyxin B-PMB), either alone or in combination, were used to eradicate the mature biofilm of Pseudomonas aeruginosa formed on Ti-6Al-4V alloy. Our aim was to find the conditions for NTP pre-treatment capable of enhancing the action of the antibiotics and thus reducing their effective concentrations. The NTP treatment increased the efficacy of relatively low concentrations of antibiotics. Generally, the highest effect was achieved with GTM, which was able to suppress the metabolic activity of pre-formed P. aeruginosa biofilms in the concentration range of 4-9 mg/L by up to 99%. In addition, an apparent decrease of biofilm-covered area was confirmed after combined NTP treatment and GTM action by SYTO®13 staining using fluorescence microscopy. Scanning electron microscopy confirmed a complete eradication of P. aeruginosa ATCC 15442 mature biofilm from Ti-6Al-4V alloy when using 0.25 h NTP treatment and subsequent treatment by 8.5 mg/L GTM. Therefore, NTP may be used as a suitable antibiofilm agent in combination with antibiotics for the treatment of biofilm-associated infections caused by this pathogen.

Aspergillus fumigatus DBM 4057 biofilm formation is inhibited by chitosan, in contrast to baicalein and rhamnolipid.

The biofilms of filamentous-forming fungi are a novel and still insufficiently understood research topic. We have studied Aspergillus fumigatus, an ubiquitous opportunistic pathogenic fungus, as a representative model for a study of biofilm formation by filamentous fungi and for assessing the potential anti-biofilm activity of natural substances. The activity of antibiotic amphotericin B and selected natural substances: baicalein, chitosan and rhamnolipid was studied. The minimum suspension inhibitory concentrations (MIC) were determined and the biofilm susceptibility was investigated by determining the metabolic activity of sessile cells (XTT assay) and total biofilm biomass (crystal violet staining). Significant time-dependent differences in substances' anti-biofilm activity were observed. Images of A. fumigatus biofilm were obtained by Cellavista automatic light microscope and spinning disc confocal microscopy. Baicalein and rhamnolipid were not found as suitable substances for inhibition of the A. fumigatus biofilm formation, as neither of the substances inhibited the sessile cells metabolic activity or the total biofilm biomass even at tenfold MIC after 48 h. In contrast, chitosan at 10 × MIC (25 µg mL-1), suppressed the biofilm metabolic activity by 90 % and the total biofilm biomass by 80 % even after 72 h of cultivation. Amphotericin B inhibited only 14 % of total biofilm biomass (crystal violet staining) and 35 % of metabolic activity (XTT assay) of adherent cells under the same conditions. Our results therefore suggest chitosan as potential alternative for treating A. fumigatus biofilm-associated infections.

Non-thermal plasma causes Pseudomonas aeruginosa biofilm release to planktonic form and inhibits production of Las-B elastase, protease and pyocyanin.

The increasing risk of antibiotic failure in the treatment of Pseudomonas aeruginosa infections is largely related to the production of a wide range of virulence factors. The use of non-thermal plasma (NTP) is a promising alternative to antimicrobial treatment. Nevertheless, there is still a lack of knowledge about the effects of NTP on the virulence factors production. We evaluated the ability of four NTP-affected P. aeruginosa strains to re-form biofilm and produce Las-B elastase, proteases, lipases, haemolysins, gelatinase or pyocyanin. Highly strains-dependent inhibitory activity of NTP against extracellular virulence factors production was observed. Las-B elastase activity was reduced up to 82% after 15-min NTP treatment, protease activity and pyocyanin production by biofilm cells was completely inhibited after 60 min, in contrast to lipases and gelatinase production, which remained unchanged. However, for all strains tested, a notable reduction in biofilm re-development ability was depicted using spinning disc confocal microscopy. In addition, NTP exposure of mature biofilms caused disruption of biofilm cells and their dispersion into the environment, as shown by transmission electron microscopy. This appears to be a key step that could help overcome the high resistance of P. aeruginosa and its eventual elimination, for example in combination with antibiotics still highly effective against planktonic cells.

Composition and Biological Activity of Vitis vinifera Winter Cane Extract on Candida Biofilm.

Vitis vinifera canes are waste material of grapevine pruning and thus represent cheap source of high-value polyphenols. In view of the fact that resistance of many pathogenic microorganisms to antibiotics is a growing problem, the antimicrobial activity of plant polyphenols is studied as one of the possible approaches. We have investigated the total phenolic content, composition, antioxidant activity, and antifungal activity against Candida biofilm of an extract from winter canes and a commercially available extract from blue grapes. Light microscopy and confocal microscopy imaging as well as crystal violet staining were used to quantify and visualize the biofilm. We found a decrease in cell adhesion to the surface depending on the concentration of resveratrol in the cane extract. The biofilm formation was observed as metabolic activity of Candida albicans, Candida parapsilosis and Candida krusei biofilm cells and the minimum biofilm inhibitory concentrations were determined. The highest inhibition of metabolic activity was observed in Candida albicans biofilm after treatment with the cane extract (30 mg/L) and blue grape extract (50 mg/L). The composition of cane extract was analyzed and found to be comparatively different from blue grape extract. In addition, the content of total phenolic groups in cane extract was three-times higher (12.75 gGA/L). The results showed that cane extract was more effective in preventing biofilm formation than blue grape extract and winter canes have proven to be a potential source of polyphenols for antimicrobial and antibiofilm treatment.

Effect of resveratrol and Regrapex-R-forte on Trichosporon cutaneum biofilm.

Microorganisms that cause chronic infections exist predominantly as surface-attached stable communities known as biofilms. Microbial cells in biofilms are highly resistant to conventional antibiotics and other forms of antimicrobial treatment; therefore, modern medicine tries to develop new drugs that exhibit anti-biofilm activity. We investigated the influence of a plant polyphenolic compound resveratrol (representative of the stilbene family) on the opportunistic pathogen Trichosporon cutaneum. Besides the influence on the planktonic cells of T. cutaneum, the ability to inhibit biofilm formation and to eradicate mature biofilm was studied. We have tested resveratrol as pure compound, as well as resveratrol in complex plant extract-the commercially available dietary supplement Regrapex-R-forte, which contains the extract of Vitis vinifera grape and extract of Polygonum cuspidatum root. Regrapex-R-forte is rich in stilbenes and other biologically active substances. Light microscopy imaging, confocal microscopy, and crystal violet staining were used to quantify and visualize the biofilm. The metabolic activity of biofilm-forming cells was studied by the tetrazolium salt assay. Amphotericin B had higher activity against planktonic cells; however, resveratrol and Regrapex-R-forte showed anti-biofilm effects, both in inhibition of biofilm formation and in the eradication of mature biofilm. The minimum biofilm eradicating concentration (MBEC80) for Regrapex-R-forte was found to be 2222 mg/L (in which resveratrol concentration is 200 mg/L). These methods demonstrated that Regrapex-R-forte can be employed as an anti-biofilm agent, as it has similar effect as amphotericin B (MBEC80 = 700 mg/L), which is routinely used in clinical practice.

Resveratrol, pterostilbene, and baicalein: plant-derived anti-biofilm agents.

Microbial adhesion to surfaces and the subsequent biofilm formation may result in contamination in food industry and in healthcare-associated infections and may significantly affect postoperative care. Some plants produce substances with antioxidant and antimicrobial properties that are able to inhibit the growth of food-borne pathogens. The aim of our study was to evaluate antimicrobial and anti-biofilm effect of baicalein, resveratrol, and pterostilbene on Candida albicans, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Escherichia coli. We determined the minimum inhibitory concentrations (MIC), the minimum adhesion inhibitory concentration (MAIC), and the minimum biofilm eradication concentration (MBEC) by crystal violet and XTT determination. Resveratrol and pterostilbene have been shown to inhibit the formation of biofilms as well as to disrupt preformed biofilms. Our results suggest that resveratrol and pterostilbene appear potentially very useful to control and inhibit biofilm contaminations by Candida albicans, Staphylococcus epidermidis, and Escherichia coli in the food industry.