Lipid-Polymer Hybrid Nanoparticles Enhance the Potency of Ampicillin against Enterococcus faecalis in a Protozoa Infection Model.

Enterococcus faecalis (E. faecalis) biofilms are implicated in endocarditis, urinary tract infections, and biliary tract infections. Coupled with E. faecalis internalization into host cells, this opportunistic pathogen poses great challenges to conventional antibiotic therapy. The inability of ampicillin (Amp) to eradicate bacteria hidden in biofilms and intracellular niches greatly reduces its efficacy against complicated E. faecalis infections. To enhance the potency of Amp against different forms of E. faecalis infections, Amp was loaded into Lipid-Polymer hybrid Nanoparticles (LPNs), a highly efficient nano delivery platform consisting of a unique combination of DOTAP lipid shell and PLGA polymeric core. The antibacterial activity of these nanoparticles (Amp-LPNs) was investigated in a protozoa infection model, achieving a much higher multiplicity of infection (MOI) compared with studies using animal phagocytes. A significant reduction of total E. faecalis was observed in all groups receiving 250 µg/mL Amp-LPNs compared with groups receiving the same concentration of free Amp during three different interventions, simulating acute and chronic infections and prophylaxis. In early intervention, no viable E. faecalis was observed after 3 h LPNs treatment whereas free Amp did not clear E. faecalis after 24 h treatment. Amp-LPNs also greatly enhanced the antibacterial activity of Amp at late intervention and boosted the survival rate of protozoa approaching 400%, where no viable protozoa were identified in the free Amp groups at the 40 h postinfection treatment time point. Prophylactic effectiveness with Amp-LPNs at a concentration of 250 µg/mL was exhibited in both bacteria elimination and protozoa survival toward subsequent infections. Using protozoa as a surrogate model for animal phagocytes to study high MOI infections, this study suggests that LPN-formulated antibiotics hold the potential to significantly improve the therapeutic outcome in highly complicated bacterial infections.

Informed Molecular Design of Conjugated Oligoelectrolytes To Increase Cell Affinity and Antimicrobial Activity.

Membrane-intercalating conjugated oligoelectrolytes (COEs) are emerging as potential alternatives to conventional, yet increasingly ineffective, antibiotics. Three readily accessible COEs, belonging to an unreported series containing a stilbene core, namely D4, D6, and D8, were designed and synthesized so that the hydrophobicity increases with increasing side-chain length. Decreased aqueous solubility correlates with increased uptake by E. coli. The minimum inhibitory concentration (MIC) of D8 is 4 µg mL-1 against both E. coli and E. faecalis, with an effective uptake of 72 %. In contrast, the MIC value of the shortest COE, D4, is 128 µg mL-1 owing to the low cellular uptake of 3 %. These findings demonstrate the application of rational design to generate efficacious antimicrobial COEs that have potential as low-cost antimicrobial agents.

Nanoscale architecture of cadherin-based cell adhesions.

Multicellularity in animals requires dynamic maintenance of cell-cell contacts. Intercellularly ligated cadherins recruit numerous proteins to form supramolecular complexes that connect with the actin cytoskeleton and support force transmission. However, the molecular organization within such structures remains unknown. Here we mapped protein organization in cadherin-based adhesions by super-resolution microscopy, revealing a multi-compartment nanoscale architecture, with the plasma-membrane-proximal cadherin-catenin compartment segregated from the actin cytoskeletal compartment, bridged by an interface zone containing vinculin. Vinculin position is determined by α-catenin, and following activation, vinculin can extend ∼30 nm to bridge the cadherin-catenin and actin compartments, while modulating the nanoscale positions of the actin regulators zyxin and VASP. Vinculin conformational activation requires tension and tyrosine phosphorylation, regulated by Abl kinase and PTP1B phosphatase. Such modular architecture provides a structural framework for mechanical and biochemical signal integration by vinculin, which may differentially engage cadherin-catenin complexes with the actomyosin machinery to regulate cell adhesions.