Suppression of planktonic and biofilm of Escherichia coli by the synergistic lantibiotics-polymyxins combinations

Escherichia coli are generally resistant to the lantibiotic's action (nisin and warnerin), but we have shown increased sensitivity of E. coli to lantibiotics in the presence of subinhibitory concentrations of polymyxins. Synergistic lantibiotic-polymyxin combinations were found for polymyxins B and M. The killing of cells at the planktonic and biofilm levels was observed for two collection and four clinical multidrug-resistant E. coli strains after treatment with lantibiotic-polymyxin B combinations. Thus, 24-h treatment of E. coli mature biofilms with warnerin-polymyxin B or nisin-polymyxin B leads to five to tenfold decrease in the number of viable cells, depending on the strain. AFM revealed that the warnerin and polymyxin B combination caused the loss of the structural integrity of biofilm and the destruction of cells within the biofilm. It has been shown that pretreatment of cells with polymyxin B leads to an increase of Ca2+ and Mg2+ ions in the culture medium, as detected by atomic absorption spectroscopy. The subsequent exposure to warnerin caused cell death with the loss of K+ ions and cell destruction with DNA and protein release. Thus, polymyxins display synergy with lantibiotics against planktonic and biofilm cells of E. coli, and can be used to overcome the resistance of Gram-negative bacteria to lantibiotics.

The Molecular Mechanisms of Oleanane Aldehyde-β-enone Cytotoxicity against Doxorubicin-Resistant Cancer Cells

Oleanane aldehyde-β-enone (OA), being the semi-synthetic derivative of the triterpenoid betulin, effectively inhibits the proliferation of HBL-100 and K562 cancer cells (IC50 0.47–0.53 µM), as well as the proliferation of their resistant subclones with high P-gp expression HBL-100/Dox, K562/i-S9 and K562/i-S9_Dox (IC50 0.45−1.24 µM). A molecular docking study, rhodamine efflux test, synergistic test with Dox, and ABC transporter gene expression were used to investigate the ability of OA to act as a P-gp substrate or inhibitor against Dox-resistant cells. We noted a trend toward a decrease in ABCB1, ABCC1 and ABCG2 expression in HBL-100 cells treated with OA. The in silico and in vitro methods suggested that OA is neither a direct inhibitor nor a competitive substrate of P-gp in overexpressing P-gp cancer cells. Thus, OA is able to overcome cellular resistance and can accumulate in Dox-resistant cells to realize toxic effects. The set of experiments suggested that OA toxic action can be attributed to activating intrinsic/extrinsic or only intrinsic apoptosis pathways in Dox-sensitive and Dox-resistant cancer cells, respectively. The cytotoxicity of OA in resistant cells is likely mediated by a mitochondrial cell death pathway, as demonstrated by positive staining with Annexin V–FITC, an increasing number of cells in the subG0/G1 phase, reactive oxygen species generation, mitochondrial dysfunction, cytochrome c migration and caspases-9,-6 activation.

The effect of sucrose-induced osmotic stress on the sensitivity ofEscherichia colito bacteriocins

Bacteriocins are antimicrobial peptides, produced by Gram-positive bacteria such as lactococci and staphylococci, that have limited bactericidal action against Gram-negative bacteria. The aim of this paper was to study the sensitivity of three strains of Escherichia coli to bacteriocins: nisin (as Nisaplin®) and two staphylococcal peptides (warnerin and hominin) during sucrose-induced osmotic stress. We found that all peptides in a 0.3 g·mL−1sucrose solution significantly reduced the number of viable E. coli. The most pronounced antibacterial effect was achieved by nisin against E. coli K-12 (3 log reduction). Slightly less bactericidal effects were observed with warnerin (1 mg·mL−1) and hominin (1 mg·mL−1) in sucrose solution. The lytic activity of staphylococcal peptides was detected by decreased optical density and viable cell counts. Moreover, it was confirmed by the increased amount of DNA and protein in the medium and the morphological changes detected by atomic force microscopy after 20 h of treatment. Zymographic analysis revealed the release of lytic enzymes from E. coli cells after treatment with staphylococcal peptides and sucrose. These results indicated that the antimicrobial action of peptides can be extended to Gram-negative bacteria via combination with high concentrations of sucrose.

Quinidine blocks adenosine 5'-triphosphate-sensitive potassium channels in heart

The ATP-sensitive potassium channel current (IK-ATP) was studied in excised inside-out patches from rat ventricular cells at 20-23 degrees C. The bath solution contained 140 mM KF, and the pipette solution contained 140 mM KCl and 1.2 mM MgCl2. ATP (0.5 mM) in the bath inhibited IK-ATP. In the absence of ATP, 10 microM quinidine decreased open probability 67 +/- 1% (n = 6) at -50 mV and 28 +/- 12% at -130 mV (n = 5) without affecting single channel conductance (48-52 pS). The block increased with 25 and 50 microM quinidine and could be reversed on washing quinidine for several minutes. Interburst (closed) intervals were increased by quinidine, whereas open and closed time distributions within bursts were not changed. We conclude that quinidine blocks IK-ATP in a "slow" and voltage-dependent manner in clinically relevant concentrations. Because of the postulated role for IK-ATP in cardiac ischemia, quinidine block of this channel may play a role in ischemic arrhythmias.