scholarly journals Autotransporter-Based Antigen Display in Bacterial Ghosts

2014 ◽  
Vol 81 (2) ◽  
pp. 726-735 ◽  
Author(s):  
Anna Hjelm ◽  
Bill Söderström ◽  
David Vikström ◽  
Wouter S. P. Jong ◽  
Joen Luirink ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Flow Cytometry ◽  
Fluorescence Microscopy ◽  
Surface Display ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Bacterial Ghosts ◽  
Cell Envelopes

ABSTRACTBacterial ghosts are empty cell envelopes of Gram-negative bacteria that can be used as vehicles for antigen delivery. Ghosts are generated by releasing the bacterial cytoplasmic contents through a channel in the cell envelope that is created by the controlled production of the bacteriophage ϕX174 lysis protein E. While ghosts possess all the immunostimulatory surface properties of the original host strain, they do not pose any of the infectious threats associated with live vaccines. Recently, we have engineered theEscherichia coliautotransporter hemoglobin protease (Hbp) into a platform for the efficient surface display of heterologous proteins in Gram-negative bacteria, HbpD. Using theMycobacterium tuberculosisvaccine target ESAT6 (early secreted antigenic target of 6 kDa), we have explored the application of HbpD to decorateE. coliandSalmonellaghosts with antigens. The use of different promoter systems enabled the concerted production of HbpD-ESAT6 and lysis protein E. Ghost formation was monitored by determining lysis efficiency based on CFU, the localization of a set of cellular markers, fluorescence microscopy, flow cytometry, and electron microscopy. Hbp-mediated surface display of ESAT6 was monitored using a combination of a protease accessibility assay, fluorescence microscopy, flow cytometry and (immuno-)electron microscopy. Here, we show that the concerted production of HbpD and lysis protein E inE. coliandSalmonellacan be used to produce ghosts that efficiently display antigens on their surface. This system holds promise for the development of safe and cost-effective vaccines with optimal intrinsic adjuvant activity and exposure of heterologous antigens to the immune system.

scholarly journals A High-Throughput Approach To Identify Compounds That Impair Envelope Integrity in Escherichia coli

2016 ◽  
Vol 60 (10) ◽  
pp. 5995-6002 ◽  
Author(s):  
Kristin R. Baker ◽  
Bimal Jana ◽  
Henrik Franzyk ◽  
Luca Guardabassi
Keyword(s):  
Escherichia Coli ◽  
High Throughput ◽  
High Throughput Screening ◽  
Gram Negative Bacteria ◽  
Chromogenic Substrate ◽  
Intrinsic Resistance ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Screening Platform

ABSTRACTThe envelope of Gram-negative bacteria constitutes an impenetrable barrier to numerous classes of antimicrobials. This intrinsic resistance, coupled with acquired multidrug resistance, has drastically limited the treatment options against Gram-negative pathogens. The aim of the present study was to develop and validate an assay for identifying compounds that increase envelope permeability, thereby conferring antimicrobial susceptibility by weakening of the cell envelope barrier in Gram-negative bacteria. A high-throughput whole-cell screening platform was developed to measureEscherichia colienvelope permeability to a β-galactosidase chromogenic substrate. The signal produced by cytoplasmic β-galactosidase-dependent cleavage of the chromogenic substrate was used to determine the degree of envelope permeabilization. The assay was optimized by using known envelope-permeabilizing compounds andE. coligene deletion mutants with impaired envelope integrity. As a proof of concept, a compound library comprising 36 peptides and 45 peptidomimetics was screened, leading to identification of two peptides that substantially increased envelope permeability. Compound 79 reduced significantly (from 8- to 125-fold) the MICs of erythromycin, fusidic acid, novobiocin and rifampin and displayed synergy (fractional inhibitory concentration index, <0.2) with these antibiotics by checkerboard assays in two genetically distinctE. colistrains, including the high-risk multidrug-resistant, CTX-M-15-producing sequence type 131 clone. Notably, in the presence of 0.25 μM of this peptide, both strains were susceptible to rifampin according to the resistance breakpoints (R> 0.5 μg/ml) for Gram-positive bacterial pathogens. The high-throughput screening platform developed in this study can be applied to accelerate the discovery of antimicrobial helper drug candidates and targets that enhance the delivery of existing antibiotics by impairing envelope integrity in Gram-negative bacteria.

scholarly journals Heterogeneous and Flexible Transmission ofmcr-1in Hospital-AssociatedEscherichia coli

mBio ◽  
2018 ◽  
Vol 9 (4) ◽  
Author(s):  
Yingbo Shen ◽  
Zuowei Wu ◽  
Yang Wang ◽  
Rong Zhang ◽  
Hong-Wei Zhou ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Genomic Analysis ◽  
Multidrug Resistant ◽  
Fluoroquinolone Resistance ◽  
Gram Negative Bacteria ◽  
Colistin Resistance ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Genes Encoding

ABSTRACTThe recent emergence of a transferable colistin resistance mechanism, MCR-1, has gained global attention because of its threat to clinical treatment of infections caused by multidrug-resistant Gram-negative bacteria. However, the possible transmission route ofmcr-1amongEnterobacteriaceaespecies in clinical settings is largely unknown. Here, we present a comprehensive genomic analysis ofEscherichia coliisolates collected in a hospital in Hangzhou, China. We found thatmcr-1-carrying isolates from clinical infections and feces of inpatients and healthy volunteers were genetically diverse and were not closely related phylogenetically, suggesting that clonal expansion is not involved in the spread ofmcr-1. Themcr-1gene was found on either chromosomes or plasmids, but in most of theE. coliisolates,mcr-1was carried on plasmids. The genetic context of the plasmids showed considerable diversity as evidenced by the different functional insertion sequence (IS) elements, toxin-antitoxin (TA) systems, heavy metal resistance determinants, and Rep proteins of broad-host-range plasmids. Additionally, the genomic analysis revealed nosocomial transmission ofmcr-1and the coexistence ofmcr-1with other genes encoding β-lactamases and fluoroquinolone resistance in theE. coliisolates. These findings indicate thatmcr-1is heterogeneously disseminated in both commensal and pathogenic strains ofE. coli, suggest the high flexibility of this gene in its association with diverse genetic backgrounds of the hosts, and provide new insights into the genome epidemiology ofmcr-1among hospital-associatedE. colistrains.IMPORTANCEColistin represents one of the very few available drugs for treating infections caused by extensively multidrug-resistant Gram-negative bacteria. The recently emergentmcr-1colistin resistance gene threatens the clinical utility of colistin and has gained global attention. Howmcr-1spreads in hospital settings remains unknown and was investigated by whole-genome sequencing ofmcr-1-carryingEscherichia coliin this study. The findings revealed extraordinary flexibility ofmcr-1in its spread among genetically diverseE. colihosts and plasmids, nosocomial transmission ofmcr-1-carryingE. coli, and the continuous emergence of novel Inc types of plasmids carryingmcr-1and newmcr-1variants. Additionally,mcr-1was found to be frequently associated with other genes encoding β-lactams and fluoroquinolone resistance. These findings provide important information on the transmission and epidemiology ofmcr-1and are of significant public health importance as the information is expected to facilitate the control of this significant antibiotic resistance threat.

scholarly journals National Surveillance of Antimicrobial Susceptibility of Bacteremic Gram-Negative Bacteria with Emphasis on Community-Acquired Resistant Isolates: Report from the 2019 Surveillance of Multicenter Antimicrobial Resistance in Taiwan (SMART)

2020 ◽  
Vol 64 (10) ◽  
Author(s):  
Po-Yu Liu ◽  
Yu-Lin Lee ◽  
Min-Chi Lu ◽  
Pei-Lan Shao ◽  
Po-Liang Lu ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Pseudomonas Aeruginosa ◽  
Antimicrobial Resistance ◽  
Klebsiella Pneumoniae ◽  
Gram Negative Bacteria ◽  
National Surveillance ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Carbapenem Resistant

ABSTRACT A multicenter collection of bacteremic isolates of Escherichia coli (n = 423), Klebsiella pneumoniae (n = 372), Pseudomonas aeruginosa (n = 300), and Acinetobacter baumannii complex (n = 199) was analyzed for susceptibility. Xpert Carba-R assay and sequencing for mcr genes were performed for carbapenem- or colistin-resistant isolates. Nineteen (67.8%) carbapenem-resistant K. pneumoniae (n = 28) and one (20%) carbapenem-resistant E. coli (n = 5) isolate harbored blaKPC (n = 17), blaOXA-48 (n = 2), and blaVIM (n = 1) genes.

scholarly journals Discovery of a Novel Class of Boron-Based Antibacterials with Activity against Gram-Negative Bacteria

2013 ◽  
Vol 57 (3) ◽  
pp. 1394-1403 ◽  
Author(s):  
Vincent Hernandez ◽  
Thibaut Crépin ◽  
Andrés Palencia ◽  
Stephen Cusack ◽  
Tsutomu Akama ◽  
...  
Keyword(s):  
Resistance Mechanisms ◽  
Trna Synthetase ◽  
Gram Negative Bacteria ◽  
Aminoacyl Trna Synthetase ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Drug Classes ◽  
Medical Need ◽  
Infection Models

ABSTRACTGram-negative bacteria cause approximately 70% of the infections in intensive care units. A growing number of bacterial isolates responsible for these infections are resistant to currently available antibiotics and to many in development. Most agents under development are modifications of existing drug classes, which only partially overcome existing resistance mechanisms. Therefore, new classes of Gram-negative antibacterials with truly novel modes of action are needed to circumvent these existing resistance mechanisms. We have previously identified a new a way to inhibit an aminoacyl-tRNA synthetase, leucyl-tRNA synthetase (LeuRS), in fungi via the oxaborole tRNA trapping (OBORT) mechanism. Herein, we show how we have modified the OBORT mechanism using a structure-guided approach to develop a new boron-based antibiotic class, the aminomethylbenzoxaboroles, which inhibit bacterial leucyl-tRNA synthetase and have activity against Gram-negative bacteria by largely evading the main efflux mechanisms inEscherichia coliandPseudomonas aeruginosa. The lead analogue, AN3365, is active against Gram-negative bacteria, includingEnterobacteriaceaebearing NDM-1 and KPC carbapenemases, as well asP. aeruginosa. This novel boron-based antibacterial, AN3365, has good mouse pharmacokinetics and was efficacious againstE. coliandP. aeruginosain murine thigh infection models, which suggest that this novel class of antibacterials has the potential to address this unmet medical need.

scholarly journals DpaA Detaches Braun’s Lipoprotein from Peptidoglycan

mBio ◽  
2021 ◽  
Vol 12 (3) ◽  
Author(s):  
Matthias Winkle ◽  
Víctor M. Hernández-Rocamora ◽  
Karthik Pullela ◽  
Emily C. A. Goodall ◽  
Alessandra M. Martorana ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Cell Envelope ◽  
Stress Conditions ◽  
Permeability Barrier ◽  
Gram Negative Bacteria ◽  
Sequence Motifs ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Impermeable Barrier

ABSTRACT Gram-negative bacteria have a unique cell envelope with a lipopolysaccharide-containing outer membrane that is tightly connected to a thin layer of peptidoglycan. The tight connection between the outer membrane and peptidoglycan is needed to maintain the outer membrane as an impermeable barrier for many toxic molecules and antibiotics. Enterobacteriaceae such as Escherichia coli covalently attach the abundant outer membrane-anchored lipoprotein Lpp (Braun’s lipoprotein) to tripeptides in peptidoglycan, mediated by the transpeptidases LdtA, LdtB, and LdtC. LdtD and LdtE are members of the same family of ld-transpeptidases but they catalyze a different reaction, the formation of 3-3 cross-links in the peptidoglycan. The function of the sixth homologue in E. coli, LdtF, remains unclear, although it has been shown to become essential in cells with inhibited lipopolysaccharide export to the outer membrane. We now show that LdtF hydrolyzes the Lpp-peptidoglycan linkage, detaching Lpp from peptidoglycan, and have renamed LdtF to peptidoglycan meso-diaminopimelic acid protein amidase A (DpaA). We show that the detachment of Lpp from peptidoglycan is beneficial for the cell under certain stress conditions and that the deletion of dpaA allows frequent transposon inactivation in the lapB (yciM) gene, whose product downregulates lipopolysaccharide biosynthesis. DpaA-like proteins have characteristic sequence motifs and are present in many Gram-negative bacteria, of which some have no Lpp, raising the possibility that DpaA has other substrates in these species. Overall, our data show that the Lpp-peptidoglycan linkage in E. coli is more dynamic than previously appreciated. IMPORTANCE Gram-negative bacteria have a complex cell envelope with two membranes and a periplasm containing the peptidoglycan layer. The outer membrane is firmly connected to the peptidoglycan by highly abundant proteins. The outer membrane-anchored Braun’s lipoprotein (Lpp) is the most abundant protein in E. coli, and about one-third of the Lpp molecules become covalently attached to tripeptides in peptidoglycan. The attachment of Lpp to peptidoglycan stabilizes the cell envelope and is crucial for the outer membrane to function as a permeability barrier for a range of toxic molecules and antibiotics. So far, the attachment of Lpp to peptidoglycan has been considered to be irreversible. We have now identified an amidase, DpaA, which is capable of detaching Lpp from peptidoglycan, and we show that the detachment of Lpp is important under certain stress conditions. DpaA-like proteins are present in many Gram-negative bacteria and may have different substrates in these species.

scholarly journals Identification and Characterization of the Major Porin of Desulfovibrio vulgaris Hildenborough

2017 ◽  
Vol 199 (23) ◽  
Author(s):  
Lucy Zeng ◽  
Etsuko Wooton ◽  
David A. Stahl ◽  
Peter J. Walian
Keyword(s):  
Electron Microscopy ◽  
Sequence Analysis ◽  
Model Organism ◽  
Desulfovibrio Vulgaris ◽  
Gram Negative Bacteria ◽  
Diverse Range ◽  
Gram Negative ◽  
Content Type ◽  
Sulfate Reducing

ABSTRACT Due in large part to their ability to facilitate the diffusion of a diverse range of solutes across the outer membrane (OM) of Gram-negative bacteria, the porins represent one of the most prominent and important bacterial membrane protein superfamilies. Notably, for the Gram-negative bacterium Desulfovibrio vulgaris Hildenborough, a model organism for studies of sulfate-reducing bacteria, no genes for porins have been identified or proposed in its annotated genome. Results from initial biochemical studies suggested that the product of the DVU0799 gene, which is one of the most abundant proteins of the D. vulgaris Hildenborough OM and purified as a homotrimeric complex, was a strong porin candidate. To investigate this possibility, this protein was further characterized biochemically and biophysically. Structural analyses via electron microscopy of negatively stained protein identified trimeric particles with stain-filled depressions and structural modeling suggested a β-barrel structure for the monomer, motifs common among the known porins. Functional studies were performed in which crude OM preparations or purified DVU0799 was reconstituted into proteoliposomes and the proteoliposomes were examined for permeability against a series of test solutes. The results obtained establish DVU0799 to be a pore-forming protein with permeability properties similar to those observed for classical bacterial porins, such as those of Escherichia coli. Taken together, these findings identify this highly abundant OM protein to be the major porin of D. vulgaris Hildenborough. Classification of DVU0799 in this model organism expands the database of functionally characterized porins and may also extend the range over which sequence analysis strategies can be used to identify porins in other bacterial genomes. IMPORTANCE Porins are membrane proteins that form transmembrane pores for the passive transport of small molecules across the outer membranes of Gram-negative bacteria. The present study identified and characterized the major porin of the model sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough, observing its preference for anionic sugars over neutral ones. Its predicted architecture appears to be novel for a classical porin, as its core β-barrel structure is of a type typically found in solute-specific channels. Broader use of the methods employed here, such as assays for channel permeability and electron microscopy of purified samples, is expected to help expand the database of confirmed porin sequences and improve the range over which sequence analysis-based strategies can be used to identify porins in other Gram-negative bacteria. Functional characterization of these critical gatekeeping proteins from divergent Desulfovibrio species should offer an improved understanding of the physiological features that determine their habitat range and supporting activities.

scholarly journals Nonclonal Emergence of Colistin Resistance Associated with Mutations in the BasRS Two-Component System in Escherichia coli Bloodstream Isolates

mSphere ◽  
2020 ◽  
Vol 5 (2) ◽  
Author(s):  
Axel B. Janssen ◽  
Toby L. Bartholomew ◽  
Natalia P. Marciszewska ◽  
Marc J. M. Bonten ◽  
Rob J. L. Willems ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Lipid A ◽  
Gram Negative Bacteria ◽  
Colistin Resistance ◽  
Anionic Lipid ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Two Component ◽  
Resistant Strains

ABSTRACT Infections by multidrug-resistant Gram-negative bacteria are increasingly common, prompting the renewed interest in the use of colistin. Colistin specifically targets Gram-negative bacteria by interacting with the anionic lipid A moieties of lipopolysaccharides, leading to membrane destabilization and cell death. Here, we aimed to uncover the mechanisms of colistin resistance in nine colistin-resistant Escherichia coli strains and one Escherichia albertii strain. These were the only colistin-resistant strains of 1,140 bloodstream Escherichia isolates collected in a tertiary hospital over a 10-year period (2006 to 2015). Core-genome phylogenetic analysis showed that each patient was colonized by a unique strain, suggesting that colistin resistance was acquired independently in each strain. All colistin-resistant strains had lipid A that was modified with phosphoethanolamine. In addition, two E. coli strains had hepta-acylated lipid A species, containing an additional palmitate compared to the canonical hexa-acylated E. coli lipid A. One E. coli strain carried the mobile colistin resistance (mcr) gene mcr-1.1 on an IncX4-type plasmid. Through construction of chromosomal transgene integration mutants, we experimentally determined that mutations in basRS, encoding a two-component signal transduction system, contributed to colistin resistance in four strains. We confirmed these observations by reversing the mutations in basRS to the sequences found in reference strains, resulting in loss of colistin resistance. While the mcr genes have become a widely studied mechanism of colistin resistance in E. coli, sequence variation in basRS is another, potentially more prevalent but relatively underexplored, cause of colistin resistance in this important nosocomial pathogen. IMPORTANCE Multidrug resistance among Gram-negative bacteria has led to the use of colistin as a last-resort drug. The cationic colistin kills Gram-negative bacteria through electrostatic interaction with the anionic lipid A moiety of lipopolysaccharides. Due to increased use in clinical and agricultural settings, colistin resistance has recently started to emerge. In this study, we used a combination of whole-genome sequence analysis and experimental validation to characterize the mechanisms through which Escherichia coli strains from bloodstream infections can develop colistin resistance. We found no evidence of direct transfer of colistin-resistant isolates between patients. The lipid A of all isolates was modified by the addition of phosphoethanolamine. In four isolates, colistin resistance was experimentally verified to be caused by mutations in the basRS genes, encoding a two-component regulatory system. Our data show that chromosomal mutations are an important cause of colistin resistance among clinical E. coli isolates.

Cell envelope analysis of Coxiella Burneti phase I and phase II

1974 ◽  
Vol 20 (10) ◽  
pp. 1465-1470 ◽  
Author(s):  
T. R. Jerrells ◽  
David J. Hinrichs ◽  
L. P. Mallavia
Keyword(s):  
Electron Microscopy ◽  
Phase I ◽  
Phase Ii ◽  
Cell Envelope ◽  
Diaminopimelic Acid ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Carbohydrate Concentration ◽  
Morphological Studies ◽  
Cell Envelopes

Cell envelopes of Coxiella burneti, Nine Mile, phase I and phase II were examined by electron microscopy and analyzed chemically in an attempt to characterize the phase phenomenon noted in this organism. Electron microscopy of intact organisms as well as cell envelope fractions revealed a morphology similar to many gram-negative bacteria and other rickettsiae. Morphological studies revealed no differences between C. burneti in phase I or II. Chemical analyses revealed a basic composition similar to that reported for members of the genus Rickettsia and many gram-negative bacteria. Cell envelopes of both phase types of this organism (I and II) contained similar amounts of extractable lipid, similar amino acid composition, and the amino sugars glucosamine and muramic acid. Diaminopimelic acid (DAP) was demonstrated in the cell envelope of both phase types. Coxiella burneti phase I differed from the phase II form in carbohydrate composition as well as protein and carbohydrate concentration. Glucuronic acid, glucose, and galactose were found in C. burneti phase I envelopes, whereas only glucose and galactose were present in phase II envelopes.

scholarly journals Bacterial Metal Resistance: Coping with Copper without Cooperativity?

mBio ◽  
2021 ◽  
Author(s):  
Nicholas P. Greene ◽  
Vassilis Koronakis
Keyword(s):  
Escherichia Coli ◽  
Cell Division ◽  
Cell Envelope ◽  
Metal Resistance ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Content Type ◽  
E Coli ◽  
Rnd Transporter ◽  
Entire Cell

In Escherichia coli and other Gram-negative bacteria, tripartite efflux pumps (TEPs) span the entire cell envelope and serve to remove noxious molecules from the cell. CusBCA is a TEP responsible for copper and silver detoxification in E. coli powered by the resistance-nodulation-cell division (RND) transporter, CusA.

How does lysozyme affect Escherichia coli: questions arising from impact frozen and freeze-substitutet bacteria

1995 ◽  
Vol 53 ◽  
pp. 876-877
Author(s):  
A. Gabrieli ◽  
P. Wild ◽  
E.M. Schraner ◽  
A. Pellegrini ◽  
R. von Fellenberg
Keyword(s):  
Electron Microscopy ◽  
Outer Membrane ◽  
Gram Negative Bacteria ◽  
Chemical Fixation ◽  
Copper Block ◽  
Gram Negative ◽  
E Coli ◽  
Muramidase Activity ◽  
Bacterial Structure ◽  
Per Se

Since the discovery by Fleming in 1922 that lysozyme has the ability to lyse Grampositive bacteria but not Gram-negative bacteria the assumption was established that lysozyme per se cannot affect Gram-negative bacteria. One basis of this assumption is that lysozyme is an enzyme with muramidase activity acting on the peptidoglycan. In E. coli, the peptoglycan layer is protected by the outer membrane, and, thus lysozyme has no access to it unless the outer membrane is destroyed, e.g. by EDTA or complement1. Accidentally, Pellegrini et al. found that lysozyme kills but does not lyse E. coli. Electron microscopy of bacteria fixed with aldehydes revealed that affected E. coli were often enlarged, the cytoplasm destroyed to various extend, but the cell membranes seem to remain intact (Fig. 1).Chemical fixation is proved to induce dramatic changes in bacterial structure. Thus we immobilized bacteria after exposure to lysozyme at 37°C for 15 min by impact freezing on a liquid nitrogen cooled copper block.

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