Silver Nanoparticle Conjugated Star PCL-b-AMPs Copolymer as Nanocomposite Exhibits Efficient Antibacterial Properties.

The traditional antibiotics have specific intracellular targets and disinfect in chemical ways, and the drug-resistance induced by the antibiotics has grown into an emerging threat. It is urgent to call for novel strategies and antibacterial materials to control this situation. Herein, we report a class of silver-decorated nanocomposite AgNPs@PCL-b-AMPs as potent nanoantibiotic, constructed by ring-opening polymerization of the monomers ε-caprolactone, Z-Lys-N-carboxyanhydrides (NCAs), and Phe-NCAs, then decorated with AgNPs, and characterized by SEM, TEM, and DLS. The biological assays revealed that the nanocomposite possessed strong antibacterial efficacy against both Gram-positive and Gram-negative bacteria including clinical isolated bacteria MRSA, VRE, P. aeruginosa, and K. pneumonia, exhibiting a MIC value range in 2-8 µg/mL. Importantly, the S. aureus and P. aeruginosa treated with the nanocomposite did not show drug-resistance even after 21 passages. Also, in vivo anti-infective assays showed that the nanocomposite was able to effectively kill bacteria in the infected viscera of mice. The study of the sterilization mechanism showed that the nanocomposite exhibited a multimodal antimicrobial mechanism, including irreversibly damaging the membrane structure, making the leakage of intracellular ions and subsequently inducing generation of the reactive oxygen species (ROS), ultimately sterilizing the bacteria. The nanocomposite exhibits effective broad-spectrum antibacterial properties and shows low toxicity to the mammalian cells/animal. Overall, the AgNPs@PCL-b-AMPs gained in this work show great potential as a highly promising antibacterial material for biomedical applications including drug-resistant bacterial infection.

Construction, mechanism, and antibacterial resistance insight into polypeptide-based nanoparticles.

The emergence of drug-resistant bacteria poses a serious threat to public health. The traditional antibiotics have specific intracellular targets and disinfect via chemical ways, which easily lead to the development of drug resistance, therefore, cationic peptides as promising antibiotic agents have attracted extensive attention due to their unique properties. Herein, we report a class of amphiphilic peptide-based pectinate polymers with primary amino groups. The polymers spontaneously self-assembled into the positively charged nanoparticles, which were evaluated and confirmed by scanning electron microscopy (SEM) and dynamic light scattering (DLS). Biological assays revealed that the nanoparticles showed broad-spectrum antibacterial efficacy against both Gram-positive and Gram-negative bacteria, exhibiting a MIC of 16 µg mL-1 against six clinical bacteria, namely, E. faecalis, S. aureus, MRSA, VRE, P. aeruginosa, and K. pneumonia, and three bacterial strains E. coli and E. coli producing NDM-1 and ImiS, and showed a sterilization rate of 95.6% and 94.7% on S. aureus and E. coli, respectively. Importantly, the nanoparticles did not result in drug-resistance for both the normal and drug-resistant bacteria tested after 14 passages and showed low toxicity on the mouse fibroblast cells (L929). The fluorescence staining, electrical conductivity, SEM, and surface plasmon resonance (SPR) characterization suggested that the nanoparticles initially bound to the surface of the bacteria, then pierced into the membranes of the bacteria with their phenyl groups, and finally disrupted the membranes, resulting in ions leaking out and thus exhibiting broad-spectrum antibacterial efficacy. This bactericidal mechanism that the nanoparticles employed does not lead the bacteria susceptible to developing drug resistance. This study provides a promising pathway for the development of the efficient antibacterial materials.

Real-time monitoring of D-Ala-D-Ala dipeptidase activity of VanX in living bacteria by isothermal titration calorimetry.

The d,d-dipeptidase enzyme VanX is the main cause of vancomycin resistance in gram-positive bacteria because of hydrolysis of the D-Ala-D-Ala dipeptide used in cell-wall biosynthesis. Continuous assay of VanX has proven challenging due to lack of a chromophoric substrate. Here, we report a direct approach for continuous assay of VanX in vitro and in vivo from hydrolysis of D-Ala-D-Ala, based on the heat-rate changes measured with isothermal titration calorimetry (ITC). With the ITC approach, determination of kinetic parameters of VanX hydrolyzing D-Ala-D-Ala and the inhibition constant of d-cysteine inhibitor yielded KM of 0.10 mM, kcat of 11.5 s-1, and Ki of 18.8 µM, which are consistent with the data from ninhydrin/Cd(II) assays. Cell-based ITC studies demonstrated that the VanX expressed in E. coli and in clinical strain VRE was inhibited by d-cysteine with IC50 values of 29.8 and 28.6 µM, respectively. Also, the total heat from D-Ala-D-Ala (4 mM) hydrolysis decreases strongly (in absolute value) from 1.26 mJ for VRE to 0.031 mJ for E. faecalis, which is consistent with the large MIC value of vancomycin of 512 µg/mL for VRE and the much smaller value of 4 µg/mL for E. faecalis. The ITC approach proposed here could be applied to screen and evaluate small molecule inhibitors of VanX or to identify drug resistant bacteria.

Amino Acid Thioesters Exhibit Inhibitory Activity against B1-B3 Subclasses of Metallo-ß-lactamases.

Superbug infection caused by metallo-ß-lactamases (MßLs) is a global public health threat. Previous studies reported that the thioesters specifically inhibited the B3 subclass MßL L1. In this work, nine amino acid thioesters 1-9 were synthesized, the activity evaluation revealed that all of these molecules exhibited broad-spectrum inhibitory efficacy against ImiS, IMP-1, NDM-1, and L1, with IC50 values range of 0.02-54.9 µM (except 5 and 7 on NDM-1), and 1 was found to be the best inhibitor with IC50 range of 0.02-16.63 µM. Minimal inhibitory concentration (MIC) assays showed that thioesters 1, 5 and 9 restored 2-32-fold antibacterial activity of cefazolin and/or imipenem against both Escherichia coli BL21 and DH10B strain expressing ImiS, L1, IMP-1 and NDM-1 (except 5 on NDM-1), and also, thioester 1 increased 2-4-fold antimicrobial activity of cefazolin on two clinical strains Pseudomonas aeruginosa and Klebsiella pneumoniae producing NDM-1. Stability evaluation indicated that thioester 1 was partially hydrolysed by MßLs to be converted into the mercaptoacetic acid, revealing that the thioester and its hydrolysate mercaptoacetic acid jointly inhibit MßLs. Isothermal titration calorimetry (ITC) monitoring showed that thioester 1 exhibited dose-dependent inhibition on four MßLs tested, and the binding of 1/L1 showed mainly enthalpy driven, while 1/NDM-1 was found to be more entropy driven. Docking studies suggested that 1 bound to Zn(II) ion(s) preferentially via its carboxylate group, while other moieties interacted mostly with the conserved active site residues.