Synergistic activity and molecular modelling of fosfomycin combinations with some antibiotics against multidrug resistant Helicobacter pylori.

Antibiotic resistance represents the main challenge of Helicobacter pylori infection worldwide. This study investigates the potential bactericidal effects of fosfomycin combinations with clarithromycin, metronidazole, ciprofloxacin, amoxicillin, rifampicin, and doxycycline against thirty-six H. pylori strains using the checkerboard and time-kill assay methods. The results showed that ≥ 50% of the strains were resistant to the six antibiotics. Remarkably, only six strains exerted resistance to these antibiotics, with the minimum inhibitory concentrations (MICs) ranges of (3.2-12.8 mg/l), (32-256 mg/l), (3.2-51.2 mg/l), (3.2-25.6 mg/l), (1.6-3.2 mg/l), and (25.6 > 51.2 mg/l), respectively. The seven antibiotics were evaluated through in silico studies for their permeability and ability to bind UDP-N-acetylglucosamine1-carboxyvinyltransferase (MurA) of H. pylori. The results indicated that fosfomycin exhibited the highest predicted membrane permeability (membrane ∆G insert = - 37.54 kcal/mol) and binding affinity (docking score = - 5.310 kcal/mol) for H. pylori MurA, compared to other tested antibiotics. The combinations of fosfomycin with these antibiotics exerted synergistic interactions (Fractional inhibitory concentration, FIC index < 1) against the six strains. Importantly, the combinations of fosfomycin with clarithromycin, doxycycline and rifampicin achieved bactericidal effects (reduction ≥ 3.0 Log10 cfu/ml) against the most resistant H. pylori strain. Notably, these effects increased with presence of metronidazole, which enhanced the activity of the fosfomycin combination with amoxicillin from a weak inhibition to bactericidal effect. This study provides evidence that the combination of fosfomycin with either clarithromycin, amoxicillin, doxycycline, or rifampicin (especially with the presence of metronidazole) could be a promising option for treating MDR H. pylori infection.

Effect of kitasamycin and nitrofurantoin at subinhibitory concentrations on quorum sensing regulated traits of Chromobacterium violaceum.

Quorum sensing (QS) is a mechanism of intercellular communication in bacteria that received substantial attention as alternate strategy for combating bacterial resistance and the development of new anti-infective agents. The present investigation reports on the assessment of using subinhibitory concentrations of antibiotics for the inhibition of QS-regulated phenotypes in Chromobacterium violaceum. Primarily, the minimum inhibitory concentrations of a series of antibiotics were determined by a microdilution method. Subsequently, the inhibitory effects of selected antibiotics on QS-regulated traits, namely violacein and chitinase production, biofilm formation and motility were evaluated using C. violaceum CV026 and C. violaceum ATCC 12472. Results revealed that kitasamycin and nitrofurantoin exhibited the highest quorum sensing inhibitory (QSI) activity. The amount of violacein produced by C. violaceum was significantly reduced in the presence of either kitasamycin or nitrofurantoin. Moreover, the chitinolytic activity, biofilm formation, and motility were also impaired in kitasamycin or nitrofurantoin-treated cultures. We further confirmed QSI effects at the molecular level using molecular docking and real-time quantitative polymerase chain reaction (RT-qPCR). Results of molecular docking suggested that both antibiotics can interact with CviR transcriptional regulator of C. violaceum. Furthermore, RT-qPCR revealed the suppressive effect of kitasamycin and nitrofurantoin on five genes under the control of the CviI/CviR system: cviI, cviR, vioB, vioC, and vioD. Giving that kitasamycin and nitrofurantoin are being safely used for decades, this study emphasizes their potential application as antivirulence agents to disarm resistant bacterial strains, making their removal an easier task for the immune system or for another antibacterial agent.

Antibacterial and anti-quorum sensing activities of a substituted thiazole derivative against methicillin-resistant Staphylococcus aureus and other multidrug-resistant bacteria.

Management of infections caused by methicillin-resistant Staphylococcus aureus (MRSA) is still challenging. We herein report the antibacterial and anti-quorum sensing (anti-QS) activities of 5-acetyl-4-methyl-2-(3-pyridyl) thiazole (AMPT) against MRSA and other multidrug-resistant bacteria. Minimum inhibitory concentrations (MICs) were determined by agar dilution method and bactericidal activity was assessed by a time-kill assay. The anti-QS activity was evaluated using Chromobacterium violaceum. The effect of AMPT on virulence factors production by MRSA and biofilm formation by MRSA, C. violaceum and Pseudomonas aeruginosa was also assessed. AMPT was superior to vancomycin and teichoplanin against MRSA isolates. MIC50/90 values of AMPT (2/4 mg/L) were 2-4 folds lower than the values for vancomycin (4/16 mg/L) and 2-fold lower than the values for teichoplanin (4/8 mg/L). Results of time-kill assay against two multidrug-resistant MRSA isolates revealed bactericidal effect of AMPT after 4 h of treatment, with no bacterial cells detected after 24 h. Remarkably, AMPT exhibited anti-QS activity against both C. violaceum and MRSA at subinhibitory concentrations. Moreover, AMPT reduced haemolysin and protease production by MRSA and inhibited biofilm formation by MRSA, C. violaceum and P. aeruginosa but had no dispersion effect on preformed ones. Furthermore, molecular docking analysis revealed promising interactions between AMPT and AgrA as well as SarA in S. aureus confirming the antivirulence and antibiofilm activities. Favourably, no significant cytotoxicity of AMPT was observed on murine macrophage cell line. Taken altogether, these results suggest that AMPT could be considered an interesting lead compound in the search for treatment of MRSA infections.

The cell envelope structure and properties of Mycobacterium smegmatis mc(2)155: is there a clue for the unique transformability of the strain?

Mycobacterium smegmatis is often used as a surrogate host for pathogenic mycobacteria, especially since the isolation of the transformable smooth morphotype strain mc(2)155 from the isogenic rough wild-type strain ATCC 607. Biochemical analysis of the cell envelope components revealed a lack of polar glycolipids, namely the lipooligosaccharides and the polar subfamilies of glycopeptidolipids, in the mc(2)155 strain. In addition, the latter strain differs from its parent by the distribution of various species of glycolipids and phospholipids between the outermost and deeper layers of the cell envelope. The presence of filamentous and rope-like structures at the cell surface of mc(2)155 cells grown in complex media further supported an ultrastructural change in the cell envelope of the mutant. Importantly, a significantly more rapid uptake of the hydrophobic chenodeoxycholate was observed for the mutant compared to wild-type cells. Taken together, these data indicate that the nature of the surface-exposed and envelope constituents is crucial for the surface properties, cell wall permeability and bacterial phenotype, and suggest that the transformable character of the mc(2)155 strain may be in part explained by these profound modifications of its cell envelope.