New antimicrobial properties of products derived from Humulus lupulus L. such as antiadherent and antibiofilm activities were evaluated. The growth of gram-positive but not gram-negative bacteria was inhibited to different extents by these compounds. An extract of hop cones containing 51% xanthohumol was slightly less active against S. aureus strains (MIC range 31.2–125.0 μg/mL) than pure xanthohumol (MIC range 15.6–62.5 μg/mL). The spent hop extract, free of xanthohumol, exhibited lower but still relevant activity (MIC range 1-2 mg/mL). There were positive coactions of hop cone, spent hop extracts, and xanthohumol with oxacillin against MSSA and with linezolid against MSSA and MRSA. Plant compounds in the culture medium at sub-MIC concentrations decreased the adhesion of Staphylococci to abiotic surfaces, which in turn caused inhibition of biofilm formation. The rate of mature biofilm eradication by these products was significant. The spent hop extract at MIC reduced biofilm viability by 42.8%, the hop cone extract by 74.8%, and pure xanthohumol by 86.5%. When the hop cone extract or xanthohumol concentration was increased, almost complete biofilm eradication was achieved (97–99%). This study reveals the potent antibiofilm activity of hop-derived compounds for the first time.

In summary, platelets even after the medical expiry date are still a good source of antimicrobial low molecular weight proteins (PMPs). Testing of bacterial resistance to PMPs may be advisable as a predictive indicator of susceptibility to treatment of infections such as infective endocarditis and other local infections of biofilm nature.

The objective was an assessment of the impact of Leonurus cardiaca L. extract (LCE) and ursolic acid (UA) on the adhesive properties of Staphylococus aureus NCTC 8325 strain, expressing virulence factors important in the pathogenesis of infective endocarditis. The adhesion and biofilm formation of bacteria cultured in the presence of subinhibitory concentrations of LCE or UA on the abiotic surface or covered with fibrinogen, fibronectin or collagen, were evaluated. Inhibitory effects of LCE and UA on staphylococcal adherence to both types of surface were demonstrated. This, in the case of UA, resulted in a significant reduction of biofilm formation.

Abstract:The aim was to provide the insight into the biology of C. albicans influenced by undescribed yet properties of saponin-rich (80%-98%) fractions (SAPFs), isolated from extracts of Trifolium alexandrinum, T. incarnatum, T. resupinatum var. resupinatum aerial parts. Their concentrations below 0.5 mg/mL were arbitrarily considered as subMICs for C. albicans ATCC 10231 and were further used. SAPFs affected yeast enzymatic activity, lowered tolerance to the oxidative stress, to the osmotic stress and to the action of the cell wall disrupting agent. In their presence, germ tubes formation was significantly and irreversibly inhibited, as well as Candida invasive capacity. The evaluation of SAPFs interactions with anti-mycotics showed synergistic activity, mainly with azoles. Fluconazole MIC was lowered-susceptible C. albicans ATCC 10231 was more susceptible, and resistant C. glabrata (clinical strain) become more susceptible (eightfold). Moreover, the tested samples showed no hemolytic activity and at the concentrations up to 0.5 mg/mL did not reduce viability of fibroblasts L929. This study provided the original evidence that SAPFs of Trifolium spp. aerial part exhibit significant antimicrobial activity, OPEN ACCESSMolecules 2014, 19 10602 by reduce the expression/quantity of important Candida virulence factors and have good potential for the development of novel antifungal products supporting classic drugs.

The aim of the study was to determine whether Leonurus cardiaca L. herb extract (LCE) used at subinhibitory concentration modifies the characteristics of Staphylococcus aureus, which is important in the pathogenesis of invasive infections originating from the bloodstream, in a way favourable for the human host. Polyphenol-rich LCE, a common ingredient in pharmaceutical products used for various cardiovascular and nervous system disorders, had shown interesting antibacterial and antibiofilm properties in our previous studies. Our current findings indicate that the following S. aureus characteristics decreased, depending on the LCE concentration: (i) formation of aggregates in plasma, (ii) adherence to a fibrin-coated surface, (iii) staphylocoagulase-dependent plasma clotting, (iv) bacterial survival in whole human blood in an ex vivo model, (v) expression of cell surface protein A and (vi) synthesis of α-toxin. However, staphylococcal tolerance to exogenous hydrogen peroxide was enhanced after pre-incubation with LCE, possibly due to the increased activity of bacterial antioxidant enzymes, a possibility confirmed by the higher production of superoxide dismutase and slightly higher production of catalase. The use of LCE at sub-MIC in in vitro and ex vivo models resulted in the weakening of some important staphylococcal immunoprotective attributes but the strengthening of such virulence factors as those responsible for oxidative stress tolerance. Some of these results and the fact that LCE has direct anticoagulant properties, reflected in a reduced thrombin-dependent fibrinogen polymerization rate, suggest a risk of adverse effects, which could be important in the context of S. aureus survival in the host.