Maxime Mourer

Cationic compounds with activity against multidrug-resistant bacteria: interest of a new compound compared with two older antiseptics, hexamidine and chlorhexidine

Use of antiseptics and disinfectants is essential in infection control practices in hospital and other healthcare settings. In this study, the in vitro activity of a new promising compound, para-guanidinoethylcalix[4]arene (Cx1), has been evaluated in comparison with hexamidine (HX) and chlorhexidine (CHX), two older cationic antiseptics. The MICs for 69 clinical isolates comprising methicillin-resistant Staphylococcus aureus, methicillin-sensitive S. aureus, coagulase-negative staphylococci (CoNS) (with or without mecA), vancomycin-resistant enterococci, Enterobacteriaceae producing various beta-lactamases and non-fermenting bacilli (Pseudomonas aeruginosa, Acinetobacter baumanii, Stenotrophomonas maltophilia) were determined. Cx1 showed similar activity against S. aureus, CoNS and Enterococcus spp., irrespective of the presence of mecA or van genes, or associated resistance genes, with very good activity against CoNS (MIC <1 mg/L). Variable activities were observed against Enterobacteriaceae; the MICs determined seemed to be dependent both on the genus (MICs of 2, 8 and 64 mg/L for Escherichia coli, Klebsiella pneumoniae and Yersinia enterocolitica, respectively) and on the resistance phenotype production of [Extended Spectrum beta-Lactase (ESBLs) or other beta-lactamases; overproduction of AmpC]. Poor activity was found against non-fermenting bacilli, irrespective of the resistance phenotype. CHX appeared to be the most active compound against all strains, with broad-spectrum and conserved activity against multidrug-resistant strains. HX showed a lower activity, essentially against Gram-positive strains. Consequently, the differences observed with respect to Cx1 suggest that they are certainly not the consequence of antibiotic resistance phenotypes, but rather the result of membrane composition modifications (e.g. of lipopolysaccharide), or of the presence of (activated) efflux-pumps. These results raise the possibility that Cx1 may be a potent new antibacterial agent of somewhat lower activity but significantly lower toxicity than CHX.

Nanoscale analysis of the effects of antibiotics and CX1 on a Pseudomonas aeruginosa multidrug-resistant strain

Drug resistance is a challenge that can be addressed using nanotechnology. We focused on the resistance of the bacteria Pseudomonas aeruginosa and investigated, using Atomic Force Microscopy (AFM), the behavior of a reference strain and of a multidrug resistant clinical strain, submitted to two antibiotics and to an innovative antibacterial drug (CX1). We measured the morphology, surface roughness and elasticity of the bacteria under physiological conditions and exposed to the antibacterial molecules. To go further in the molecules action mechanism, we explored the bacterial cell wall nanoscale organization using functionalized AFM tips. We have demonstrated that affected cells have a molecularly disorganized cell wall; surprisingly long molecules being pulled off from the cell wall by a lectin probe. Finally, we have elucidated the mechanism of action of CX1: it destroys the outer membrane of the bacteria as demonstrated by the results on artificial phospholipidic membranes and on the resistant strain.

Towards calixarene-based prodrugs: Drug release and antibacterial behaviour of a water-soluble nalidixic acid/calix[4]arene ester adduct

A water-soluble calixarene-based heterocyclic podand incorporating a quinolone antibiotic subunit, the nalidixic acid, was synthesised and fully characterised. Its prodrug behaviour was assessed in vitro by HPLC, demonstrating the release of the tethered quinolone in model biological conditions. Microbiological studies performed on various Gram-positive and Gram-negative reference strains showed very interesting antibacterial activities.

Antiseptic properties of two calix[4]arenes derivatives on the human coronavirus 229E

Abstract Facing the lack in specific antiviral treatment, it is necessary to develop new means of prevention. In the case of the Coronaviridae this family is now recognized as including potent human pathogens causing upper and lower respiratory tract infections as well as nosocomial ones. Within the purpose of developing new antiseptics molecules, the antiseptic virucidal activity of two calix[4]arene derivatives, the tetra-para-sulfonato-calix[4]arene (C[4]S) and the 1,3-bis(bithiazolyl)-tetra-para-sulfonato-calix[4]arene (C[4]S-BTZ) were evaluated toward the human coronavirus 229E (HCoV 229E). Comparing these results with some obtained previously with chlorhexidine and hexamidine, (i) these two calixarenes did not show any cytotoxicity contrary to chlorhexidine and hexamidine, (ii) C[4]S showed as did hexamidine, a very weak activity against HCoV 229E, and (iii) the C[4]S-BTZ showed a stronger activity than chlorhexidine, i.e. 2.7 and 1.4log10 reduction in viral titer after 5min of contact with 10−3 molL−1 solutions of C[4]S-BTZ and chlorhexidine, respectively. Thus, the C[4]S-BTZ appeared as a promising virucidal (antiseptic) molecule.

Guanidinium compounds with sub-micromolar activities against Mycobacterium tuberculosis. Synthesis, characterization and biological evaluations

Seven polycharged species, incorporating 1, 2, 3, 4 and 6 guanidine arms organized around a benzene core were synthesized and assayed as anti-mycobacterial agents against Mycobacterium tuberculosis. They display MIC values comprised between 25 and 12.5 μM (close to ethambutol EMB) for the mono- and the hexa-substituted derivatives, and 0.8 μM (close to isoniazid and streptomycin) for the tri-substituted derivative. The three bi- and the tetra-substituted analogs displayed MIC values of ca. 6.5-3.0 μM. The latter were also evaluated against the isoniazid-resistant MYC5165 strain, resulting in highly interesting micromolar or sub-micromolar MIC, ca. 4-125 times more active than isoniazid. These preliminary results are attractive for the development of new anti-TB agents.

The selective interactions of cationic tetra-p-guanidinoethylcalix[4]arene with lipid membranes: theoretical and experimental model studies

Behavior of cationic tetra-p-guanidinoethylcalix[4]arene (CX1) and its building block, p-guanidinoethylphenol (mCX1) in model monolayer lipid membranes was investigated using all atom molecular dynamics simulations and surface pressure measurements. Members of two classes of lipids were taken into account: zwitterionic 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) and anionic 1,2-dimyristoyl-sn-glycero-3-phospho-l-serine sodium salt (DMPS) as models of eukaryotic and bacterial cell membranes, respectively. It was demonstrated that CX1 and mCX1 accumulate near the negatively charged DMPS monolayers. The adsorption to neutral monolayers was negligible. In contrast to mCX1, CX1 penetrated into the hydrophobic part of the monolayer. The latter effect, which is possible due to a flip-flop inversion of the CX1 orientation in the lipid layer compared to the aqueous phase, may be responsible for its antibacterial activity.

Poly-guanidinoethylphenylethers organised around a benzene ring: Synthesis and evaluation of their antibacterial and cytotoxic properties

A new family of poly-guanidinium species with a benzene core as the organising agent has been developed. Their antibacterial properties have been evaluated against reference Gram positive and Gram negative bacteria, and their cytotoxicity against eukaryotic cells. Most of these compounds exhibited Minimum Inhibitory Concentrations in the micromolar range.

A bacteriophilic resin, synthesis and E. coli sequestration study

The poly-cationic pyridinium-Merrifield resin I was prepared and characterized by elemental analysis, infrared spectroscopy and SEM, with a loading of 2.96 × 10−3 mol of pyridinium chloride groups per gram. Its sequestering properties towards bacteria were evaluated, using E. coli as a model. The capture of E. coli was followed by Capillary Electrophoresis (CE) that showed the effectiveness and the celerity of the capture, i.e. around 90% of cells after 3 h of contact. The bacterial loading was evaluated at 7 mg bacteria per g resin. The bacteriophilic behaviour of resin I was confirmed by confocal microscopy which evidenced the presence of bacteria at the surface of the beads. Attempts to correlate CE capture results to bacterial counting at the surface of beads are presented.

Synthesis and evaluation of 1,ω-bis(1,2,3,5-thiatriazol-5-yl)alkanes as in vitro and in vivo α-amylase and lipase inhibitors.

Thionyl chloride reacts with 1,ω‐bis‐(1‐tosylamidrazone)alkanes 1 to give a series of 1,ω‐bis‐(4‐alkyl‐2‐tosyl‐1,2,3,5‐thiatriazol‐5‐yl)alkanes 2. All the newly synthesized compounds were characterized by IR, 1H NMR, 13C NMR, elemental analysis, and ESI–MS spectral data. All the new compounds were screened for their inhibitory effect on key enzymes related to diabetes and obesity, such as α‐amylase and lipase. In vitro and in vivo studies revealed that these thiatriazole derivatives exert an inhibitory action against these key enzymes. Moreover the administration of these compounds to surviving diabetic rats induced a significant decrease in plasma glucose level. Additively 2d significantly protected the liver–kidney functions and modulated lipid metabolism, which were evidenced by the decrease in aspartate transaminase (AST), alanine transaminase (ALT), and gamma‐glutamyl transpeptidase (GGT) activities and creatinine, urea albumin, LDL‐cholesterol and triglycerides levels as well as an increase in the HDL‐cholesterol level in surviving diabetic rats. Overall, the findings of the current study indicate that 2d exhibits attractive properties and can, therefore, be considered for future application in the development of anti‐diabetic and hypolipidemic drugs.

Bacteriophilic tetra-p-guanidinoethyl-calix[4]arene derived polymers. Syntheses and E. coli sequestration studies

The antibacterial tetracationic tetra-p-guanidinoethylcalix[4]arene developed by our team has been anchored through bottom-up or top-down pathways to the surface of Merrifield and Wang benzaldehyde resins; the attachment involved either a pyridinium linker or an imine/amine one. The grafting yields were evaluated by elemental analysis through the nitrogen content. Their sequestering properties towards bacteria were evaluated, using E. coli as a model, by capillary electrophoresis (CE) which showed their efficiencies and their bacteriophilic behaviors. All the new materials were compared to two pyridinium-derived Merrifield resins in terms of effective capture, efficiency, and removal coefficients, showing that some of these calixarene-derived resins are good bacteriophilic materials. Confirmation of such behavior has been provided by microscopy.