MCR-1 is a lipid A modifying enzyme that confers resistance to the antibiotic colistin. Here, we analyse the impact of MCR-1 expression on E. coli morphology, fitness, competitiveness, immune stimulation and virulence. Increased expression of mcr-1 results in decreased growth rate, cell viability, competitive ability and significant degradation in cell membrane and cytoplasmic structures, compared to expression of catalytically inactive MCR-1 (E246A) or MCR-1 soluble component. Lipopolysaccharide (LPS) extracted from mcr-1 strains induces lower production of IL-6 and TNF, when compared to control LPS. Compared to their parent strains, high-level colistin resistance mutants (HLCRMs) show reduced fitness (relative fitness is 0.41–0.78) and highly attenuated virulence in a Galleria mellonella infection model. Furthermore, HLCRMs are more susceptible to most antibiotics than their respective parent strains. Our results show that the bacterium is challenged to find a delicate equilibrium between expression of MCR-1-mediated colistin resistance and minimalizing toxicity and thus ensuring cell survival.

Acquisition of a mucoid phenotype by Pseudomonas sp. in the lungs of cystic fibrosis (CF) patients, with subsequent over-production of extracellular polymeric substance (EPS), plays an important role in mediating the persistence of multi-drug resistant (MDR) infections. The ability of a low molecular weight (Mn = 3200 g mol−1) alginate oligomer (OligoG CF-5/20) to modify biofilm structure of mucoid Pseudomonas aeruginosa (NH57388A) was studied in vitro using scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) with Texas Red (TxRd®)-labelled OligoG and EPS histochemical staining. Structural changes in treated biofilms were quantified using COMSTAT image-analysis software of CLSM z-stack images, and nanoparticle diffusion. Interactions between the oligomers, Ca2+ and DNA were studied using molecular dynamics (MD) simulations, Fourier transform infrared spectroscopy (FTIR) and isothermal titration calorimetry (ITC). Imaging demonstrated that OligoG treatment (≥0.5%) inhibited biofilm formation, revealing a significant reduction in both biomass and biofilm height (P < 0.05). TxRd®-labelled oligomers readily diffused into established (24 h) biofilms. OligoG treatment (≥2%) induced alterations in the EPS of established biofilms; significantly reducing the structural quantities of EPS polysaccharides, and extracellular (e)DNA (P < 0.05) with a corresponding increase in nanoparticle diffusion (P < 0.05) and antibiotic efficacy against established biofilms. ITC demonstrated an absence of rapid complex formation between DNA and OligoG and confirmed the interactions of OligoG with Ca2+ evident in FTIR and MD modelling. The ability of OligoG to diffuse into biofilms, potentiate antibiotic activity, disrupt DNA-Ca2+-DNA bridges and biofilm EPS matrix highlights its potential for the treatment of biofilm-related infections.

This paper describes the synthesis and structure-activity relationships (SAR) leading to the first rational design of "dipeptoid" analogues of the neuropeptide cholecystokinin (CCK). Compounds [R-(R*,S*)]-4-[2-[3-(1H-indol-3-yl)-2-methyl-1-oxo-2-[(tricyclo [3.3.1.1(3,7)]dec-2-yloxy)carbonyl]amino]propyl]amino]-3- phenylpropyl]-amino]-4-oxo-2-butenoic acid, [R-(R*,R*)]-4-[2-[3-(1H-indol-3-yl)-2-methyl-1-oxo-2-[(tricyclo [3.3.1.1(3,7)]dec-2-oxy)carbonyl]amino]propyl]amino]-1- phenylethyl]amino]-4-oxo-2-butenoic acid, and [R-(R*,R*)]-4-[2-[3-(1H-indol-3-yl)-2-methyl-1-oxo-2-[(tricyclo [3.3.1.1(3,7)]dec-2-yloxy)carbonyl]amino]propyl]amino]-1- phenylethyl]amino]-4-oxobutanoic acid (29d) have CCK-B binding affinities of IC50 = 0.8, 0.7, and 1.7 nM with a CCK-A/CCK-B ratio of 550, 1100, and 2500, respectively. Compound 27 is well-absorbed and is equiactive by the subcutaneous (sc) and intravenous (iv) routes of administration in the Ghosh and Schild test in rats in inhibiting pentagastrin stimulated gastric acid secretion with ED50 = 0.07 (0.01-0.34) mumol/kg. Compound 29d is anxiolytic in mice in the black-white test box over the range 0.0001-30 mg/kg sc, comparable in activity to diazepam over the range 0.125-1 mg/kg ip), and also active in this test when dosed orally over a wide range from 0.0001 to 10 mg/kg.

The host- and bacteria-derived extracellular polysaccharide coating of the lung is a considerable challenge in chronic respiratory disease and is a powerful barrier to effective drug delivery. A low molecular weight 12-15-mer alginate oligosaccharide (OligoG CF-5/20), derived from plant biopolymers, was shown to modulate the polyanionic components of this coating. Molecular modeling and Fourier transform infrared spectroscopy demonstrated binding between OligoG CF-5/20 and respiratory mucins. Ex vivo studies showed binding induced alterations in mucin surface charge and porosity of the three-dimensional mucin networks in cystic fibrosis (CF) sputum. Human studies showed that OligoG CF-5/20 is safe for inhalation in CF patients with effective lung deposition and modifies the viscoelasticity of CF-sputum. OligoG CF-5/20 is the first inhaled polymer therapy, represents a novel mechanism of action and therapeutic approach for the treatment of chronic respiratory disease, and is currently in Phase IIb clinical trials for the treatment of CF.

Pseudomonas aeruginosa (PA) biofilm-associated infections are a common cause of morbidity in chronic respiratory disease and represent a therapeutic challenge. Recently, the ability of a novel alginate oligomer (OligoG) to potentiate the effect of antibiotics against gram-negative, multi-drug-resistant bacteria and inhibit biofilm formation in vitro has been described. Interaction of OligoG with the cell surface of PA was characterized at the nanoscale using atomic force microscopy (AFM), zeta potential measurement (surface charge), and sizing measurements (dynamic light scattering). The ability of OligoG to modify motility was studied in motility assays. AFM demonstrated binding of OligoG to the bacterial cell surface, which was irreversible after exposure to hydrodynamic shear (5,500 × g). Zeta potential analysis (pH 5-9; 0.1-0.001 M NaCl) demonstrated that binding was associated with marked changes in the bacterial surface charge (-30.9 ± 0.8 to -47.0 ± 2.3 mV; 0.01 M NaCl [pH 5]; P < 0.001). Sizing analysis demonstrated that alteration of surface charge was associated with cell aggregation with a 2- to 3-fold increase in mean particle size at OligoG concentrations greater than 2% (914 ± 284 to 2599 ± 472 nm; 0.01 M NaCl [pH 5]; P < 0.001). These changes were associated with marked dose-dependent inhibition in bacterial swarming motility in PA and Burkholderia spp. The ability of OligoG to bind to a bacterial surface, modulate surface charge, induce microbial aggregation, and inhibit motility represents important direct mechanisms by which antibiotic potentiation and biofilm disruption is affected. These results highlight the value of combining multiple nanoscale technologies to further our understanding of the mechanisms of action of novel antibacterial therapies.