Host-guest chemistry of the peptidoglycan

Antibacterial Properties of Graphene-Based Nanomaterials

Bacteria mediated infections may cause various acute or chronic illnesses and antibiotic resistance in pathogenic bacteria has become a serious health problem around the world due to their excessive use or misuse. Replacement of existing antibacterial agents with a novel and efficient alternative is the immediate demand to alleviate this problem. Graphene-based materials have been exquisitely studied because of their remarkable bactericidal activity on a wide range of bacteria. Graphene-based materials provide advantages of easy preparation, renewable, unique catalytic properties, and exceptional physical properties such as a large specific surface area and mechanical strength. However, several queries related to the mechanism of action, significance of size and composition toward bacterial activity, toxicity criteria, and other issues are needed to be addressed. This review summarizes the recent efforts that have been made so far toward the development of graphene-based antibacterial materials to face current challenges to combat against the bacterial targets. This review describes the inherent antibacterial activity of graphene-family and recent advances that have been made on graphene-based antibacterial materials covering the functionalization with silver nanoparticles, other metal ions/oxides nanoparticles, polymers, antibiotics, and enzymes along with their multicomponent functionalization. Furthermore, the review describes the biosafety of the graphene-based antibacterial materials. It is hoped that this review will provide valuable current insight and excite new ideas for the further development of safe and efficient graphene-based antibacterial materials.

Vancomycin-conjugated polythiophene for the detection and imaging of Gram-positive bacteria

Vancomycin-conjugated polythiophene was synthesized for the discrimination and elimination of Gram-positive bacteria.

Biofilm formation in total hip arthroplasty: prevention and treatment

This review assesses the current knowledge on treatments, pathogenesis and the prevention of infections associated with orthopaedic implants, with a focus on total hip arthroplasty.

Glycopeptide antibiotic analogs for selective inactivation and two-photon imaging of vancomycin-resistant strains

Theranostic divalent vancomycin systems exhibit selective antibacterial activity against vancomycin-resistant strains and can be applied for two-photon fluorescence imaging.

Structure and cell wall cleavage by modular lytic transglycosylase MltC of Escherichia coli

The lytic transglycosylases are essential bacterial enzymes that catalyze the nonhydrolytic cleavage of the glycan strands of the bacterial cell wall. We describe here the structural and catalytic properties of MltC, one of the seven lytic transglycosylases found in the genome of the Gram-negative bacterium Escherichia coli. The 2.3 Å resolution X-ray structure of a soluble construct of MltC shows a unique, compared to known lytic transglycosylase structures, two-domain structure characterized by an expansive active site of 53 Å length extending through an interface between the domains. The structures of three complexes of MltC with cell wall analogues suggest the positioning of the peptidoglycan in the active site both as a substrate and as a product. One complex is suggested to correspond to an intermediate in the course of sequential and exolytic cleavage of the peptidoglycan. Moreover, MltC partitioned its reactive oxocarbenium-like intermediate between trapping by the C6-hydroxyl of the muramyl moiety (lytic transglycosylase activity, the major path) and by water (muramidase activity). Genomic analysis identifies the presence of an MltC homologue in no less than 791 bacterial genomes. While the role of MltC in cell wall assembly and maturation remains uncertain, we propose a functional role for this enzyme as befits the uniqueness of its two-domain structure.

Early insights into the interactions of different β-lactam antibiotics and β-lactamase inhibitors against soluble forms of Acinetobacter baumannii PBP1a and Acinetobacter sp. PBP3

Acinetobacter baumannii is an increasingly problematic pathogen in United States hospitals. Antibiotics that can treat A. baumannii are becoming more limited. Little is known about the contributions of penicillin binding proteins (PBPs), the target of β-lactam antibiotics, to β-lactam-sulbactam susceptibility and β-lactam resistance in A. baumannii. Decreased expression of PBPs as well as loss of binding of β-lactams to PBPs was previously shown to promote β-lactam resistance in A. baumannii. Using an in vitro assay with a reporter β-lactam, Bocillin, we determined that the 50% inhibitory concentrations (IC(50)s) for PBP1a from A. baumannii and PBP3 from Acinetobacter sp. ranged from 1 to 5 μM for a series of β-lactams. In contrast, PBP3 demonstrated a narrower range of IC(50)s against β-lactamase inhibitors than PBP1a (ranges, 4 to 5 versus 8 to 144 μM, respectively). A molecular model with ampicillin and sulbactam positioned in the active site of PBP3 reveals that both compounds interact similarly with residues Thr526, Thr528, and Ser390. Accepting that many interactions with cell wall targets are possible with the ampicillin-sulbactam combination, the low IC(50)s of ampicillin and sulbactam for PBP3 may contribute to understanding why this combination is effective against A. baumannii. Unraveling the contribution of PBPs to β-lactam susceptibility and resistance brings us one step closer to identifying which PBPs are the best targets for novel β-lactams.

Messenger functions of the bacterial cell wall-derived muropeptides

Bacterial muropeptides are soluble peptidoglycan structures central to recycling of the bacterial cell wall and messengers in diverse cell signaling events. Bacteria sense muropeptides as signals that antibiotics targeting cell-wall biosynthesis are present, and eukaryotes detect muropeptides during the innate immune response to bacterial infection. This review summarizes the roles of bacterial muropeptides as messengers, with a special emphasis on bacterial muropeptide structures and the relationship of structure to the biochemical events that the muropeptides elicit. Muropeptide sensing and recycling in both Gram-positive and Gram-negative bacteria are discussed, followed by muropeptide sensing by eukaryotes as a crucial event in the innate immune response of insects (via peptidoglycan-recognition proteins) and mammals (through Nod-like receptors) to bacterial invasion.

Identification of products of inhibition of GES-2 beta-lactamase by tazobactam by x-ray crystallography and spectrometry

The GES-2 β-lactamase is a class A carbapenemase, the emergence of which in clinically important bacterial pathogens is a disconcerting development as the enzyme confers resistance to carbapenem antibiotics. Tazobactam is a clinically used inhibitor of class A β-lactamases, which inhibits the GES-2 enzyme effectively, restoring susceptibility to β-lactam antibiotics. We have investigated the details of the mechanism of inhibition of the GES-2 enzyme by tazobactam. By the use of UV spectrometry, mass spectroscopy, and x-ray crystallography, we have documented and identified the involvement of a total of seven distinct GES-2·tazobactam complexes and one product of the hydrolysis of tazobactam that contribute to the inhibition profile. The x-ray structures for the GES-2 enzyme are for both the native (1.45 Å) and the inhibited complex with tazobactam (1.65 Å). This is the first such structure of a carbapenemase in complex with a clinically important β-lactam inhibitor, shedding light on the structural implications for the inhibition process.

Bactericidal core-shell paramagnetic nanoparticles functionalized with poly(hexamethylene biguanide)

Bactericidal paramagnetic particles were obtained either through the attachment of a conjugate of poly(ethyleneimine) (PEI) and poly(hexamethylene biguanide) (PHMBG) to the surface of magnetite (Fe(3)O(4)) particles, or via the sol-gel encapsulation of magnetite particles with a functional silane (3-glycidoxypropyl trimethoxysilane) and subsequent binding of the polysiloxane shell by the amine/imine groups of PHMBG. The encapsulated core-shell particles possess a high saturation magnetization, which is preserved for more than 10 months while in contact with air in aqueous suspensions. The minimum inhibitory concentration (MIC) of the encapsulated particles for eight types of bacteria was size-dependent, with polydisperse submillimeter particles possessing a several-fold higher MIC than analogous particles sized below 250 nm. The encapsulated particles are biocompatible and nontoxic to mammalian cells such as mouse fibroblasts. The particles efficiently bind both glycopeptide components mimicking the gram-positive bacteria membranes and whole bacteria, and possess broad-range bactericidal activity. The cell-particle complexes can be captured, manipulated, and removed by means of a magnet.