scholarly journals Outer membrane permeability of the antibiotic-supersusceptible lipid A mutants of Escherichia coli to hydrophobic steroid probes

1999 ◽  
Vol 43 (4) ◽  
pp. 608-610 ◽  
Author(s):  
P. Plesiat ◽  
M. Vaara
Keyword(s):  
Escherichia Coli ◽  
Membrane Permeability ◽  
Outer Membrane ◽  
Lipid A ◽  
Outer Membrane Permeability

scholarly journals Outer Membrane Permeability Barrier in Escherichia coli Mutants That Are Defective in the Late Acyltransferases of Lipid A Biosynthesis

1999 ◽  
Vol 43 (6) ◽  
pp. 1459-1462 ◽  
Author(s):  
Martti Vaara ◽  
Marjatta Nurminen
Keyword(s):  
Escherichia Coli ◽  
Membrane Permeability ◽  
Outer Membrane ◽  
Lipid A ◽  
Enteric Bacteria ◽  
Normal Function ◽  
Permeability Barrier ◽  
Core Oligosaccharide ◽  
Hydrophobic Solutes ◽  
Outer Membrane Permeability

ABSTRACT The tight packing of six fatty acids in the lipid A constituent of lipopolysaccharide (LPS) has been proposed to contribute to the unusually low permeability of the outer membrane of gram-negative enteric bacteria to hydrophobic antibiotics. Here it is shown that theEscherichia coli msbB mutant, which elaborates defective, penta-acylated lipid A, is practically as resistant to a representative set of hydrophobic solutes (rifampin, fusidic acid, erythromycin, clindamycin, and azithromycin) as the parent-type control strain. The susceptibility index, i.e., the approximate ratio between the MIC for the msbB mutant and that for the parent-type control, was maximally 2.7-fold. In comparison, the rfa mutant defective in the deep core oligosaccharide part of LPS displayed indices ranging from 20 to 64. The lpxA and lpxD lipid A mutants had indices higher than 512. Furthermore, the msbBmutant was resistant to glycopeptides (vancomycin, teicoplanin), whereas the rfa, lpxA, and lpxDmutants were susceptible. The msbB htrB double mutant, which elaborates even-more-defective, partially tetra-acylated lipid A, was still less susceptible than the rfa mutant. These findings indicate that hexa-acylated lipid A is not a prerequisite for the normal function of the outer membrane permeability barrier.

scholarly journals YejM Controls LpxC Levels by Regulating Protease Activity of the FtsH/YciM Complex of Escherichia coli

2020 ◽  
Vol 202 (18) ◽  
Author(s):  
Daniel Nguyen ◽  
Keilen Kelly ◽  
Nan Qiu ◽  
Rajeev Misra
Keyword(s):  
Escherichia Coli ◽  
Membrane Permeability ◽  
Outer Membrane ◽  
Lipid A ◽  
Novel Mutation ◽  
Lipid Homeostasis ◽  
Permeability Barrier ◽  
Suppressor Mutations ◽  
Common Precursor ◽  
Outer Membrane Permeability

ABSTRACT LpxC is a deacetylase that catalyzes the first committed step of lipid A biosynthesis in Escherichia coli. LpxC competes for a common precursor, R-3-hydroxymyristoyl-UDP-GlcNAc, with FabZ, whose dehydratase activity catalyzes the first committed step of phospholipid biosynthesis. To maintain the optimum flow of the common precursor to these two competing pathways, the LpxC level is controlled by FtsH/YciM-mediated proteolysis. It is not known whether this complex or another protein senses the status of lipid A synthesis to control LpxC proteolysis. The work carried out in this study began with a novel mutation, yejM1163, which causes hypersensitivity to large antibiotics such as vancomycin and erythromycin. Isolates resistant to these antibiotics carried suppressor mutations in the ftsH and yciM genes. Western blot analysis showed a dramatically reduced LpxC level in the yejM1163 background, while the presence of ftsH or yciM suppressor mutations restored LpxC levels to different degrees. Based on these observations, it is proposed that YejM is a sensor of lipid A synthesis and controls LpxC levels by modulating the activity of the FtsH/YciM complex. The truncation of the periplasmic domain in the YejM1163 protein causes unregulated proteolysis of LpxC, thus diverting a greater pool of R-3-hydroxymyristoyl-UDP-GlcNAc toward phospholipid synthesis. This imbalance in lipid synthesis perturbs the outer membrane permeability barrier, causing hypersensitivity toward vancomycin and erythromycin. yejM1163 suppressor mutations in ftsH and yciM lower the proteolytic activity toward LpxC, thus restoring lipid homeostasis and the outer membrane permeability barrier. IMPORTANCE Lipid homeostasis is critical for proper envelope functions. The level of LpxC, which catalyzes the first committed step of lipopolysaccharide (LPS) synthesis, is controlled by an essential protease complex comprised of FtsH and YciM. Work carried out here suggests YejM, an essential envelope protein, plays a central role in sensing the state of LPS synthesis and controls LpxC levels by regulating the activity of FtsH/YciM. All four essential proteins are attractive targets of therapeutic development.

scholarly journals Importance of Real-Time Assays To Distinguish Multidrug Efflux Pump-Inhibiting and Outer Membrane-Destabilizing Activities in Escherichia coli

2015 ◽  
Vol 197 (15) ◽  
pp. 2479-2488 ◽  
Author(s):  
Rajeev Misra ◽  
Keith D. Morrison ◽  
Hyun Jae Cho ◽  
Thanh Khuu
Keyword(s):  
Escherichia Coli ◽  
Membrane Permeability ◽  
Outer Membrane ◽  
Real Time ◽  
Efflux Pump ◽  
Membrane Integrity ◽  
Efflux Pumps ◽  
Permeability Barrier ◽  
Multidrug Efflux ◽  
Outer Membrane Permeability

ABSTRACTThe constitutively expressed AcrAB multidrug efflux system ofEscherichia colishows a high degree of homology with the normally silent AcrEF system. Exposure of a strain withacrABdeleted to antibiotic selection pressure frequently leads to the insertion sequence-mediated activation of the homologous AcrEF system. In this study, we used strains constitutively expressing either AcrAB or AcrEF from their normal chromosomal locations to resolve a controversy about whether phenylalanylarginine β-naphthylamide (PAβN) inhibits the activities of AcrAB and AcrEF and/or acts synergistically with antibiotics by destabilizing the outer membrane permeability barrier. Real-time efflux assays allowed a clear distinction between the efflux pump-inhibiting activity of PAβN and the outer membrane-destabilizing action of polymyxin B nonapeptide (PMXBN). When added in equal amounts, PAβN, but not PMXBN, strongly inhibited the efflux activities of both AcrAB and AcrEF pumps. In contrast, when outer membrane destabilization was assessed by the nitrocefin hydrolysis assay, PMXBN exerted a much greater damaging effect than PAβN. Strong action of PAβN in inhibiting efflux activity compared to its weak action in destabilizing the outer membrane permeability barrier suggests that PAβN acts mainly by inhibiting efflux pumps. We concluded that at low concentrations, PAβN acts specifically as an inhibitor of both AcrAB and AcrEF efflux pumps; however, at high concentrations, PAβN in the efflux-proficient background not only inhibits efflux pump activity but also destabilizes the membrane. The effects of PAβN on membrane integrity are compounded in cells unable to extrude PAβN.IMPORTANCEThe increase in multidrug-resistant bacterial pathogens at an alarming rate has accelerated the need for implementation of better antimicrobial stewardship, discovery of new antibiotics, and deeper understanding of the mechanism of drug resistance. The work carried out in this study highlights the importance of employing real-time fluorescence-based assays in differentiating multidrug efflux-inhibitory and outer membrane-destabilizing activities of antibacterial compounds.

scholarly journals Role of Porins in Sensitivity of Escherichia coli to Antibacterial Activity of the Lactoperoxidase Enzyme System

2005 ◽  
Vol 71 (7) ◽  
pp. 3512-3518 ◽  
Author(s):  
Philipp De Spiegeleer ◽  
Jan Sermon ◽  
Kristof Vanoirbeek ◽  
Abram Aertsen ◽  
Chris W. Michiels
Keyword(s):  
Escherichia Coli ◽  
Membrane Permeability ◽  
Outer Membrane ◽  
Enzyme System ◽  
Polyacrylamide Gel Electrophoresis ◽  
Sodium Dodecyl ◽  
Core Oligosaccharide ◽  
Nitrophenyl Phosphate ◽  
Oligosaccharide Moiety ◽  
Outer Membrane Permeability

ABSTRACT Lactoperoxidase is an enzyme that contributes to the antimicrobial defense in secretory fluids and that has attracted interest as a potential biopreservative for foods and other perishable products. Its antimicrobial activity is based on the formation of hypothiocyanate (OSCN−) from thiocyanate (SCN−), using H2O2 as an oxidant. To gain insight into the antibacterial mode of action of the lactoperoxidase enzyme system, we generated random transposon insertion mutations in Escherichia coli MG1655 and screened the resultant mutants for an altered tolerance of bacteriostatic concentrations of this enzyme system. Out of the ca. 5,000 mutants screened, 4 showed significantly increased tolerance, and 2 of these had an insertion, one in the waaQ gene and one in the waaO gene, whose products are involved in the synthesis of the core oligosaccharide moiety of lipopolysaccharides. Besides producing truncated lipopolysaccharides and displaying hypersensitivity to novobiocin and sodium dodecyl sulfate (SDS), these mutants were also shown by urea-SDS-polyacrylamide gel electrophoresis analysis to have reduced amounts of porins in their outer membranes. Moreover, they showed a reduced degradation of p-nitrophenyl phosphate and an increased resistance to ampicillin, two indications of a decrease in outer membrane permeability for small hydrophilic solutes. Additionally, ompC and ompF knockout mutants displayed levels of tolerance to the lactoperoxidase system similar to those displayed by the waa mutants. These results suggest that mutations which reduce the porin-mediated outer membrane permeability for small hydrophilic molecules lead to increased tolerance to the lactoperoxidase enzyme system because of a reduced uptake of OSCN−.

scholarly journals Antibiotic Trapping by Plasmid-Encoded CMY-2 β-Lactamase Combined with Reduced Outer Membrane Permeability as a Mechanism of Carbapenem Resistance in Escherichia coli

2013 ◽  
Vol 57 (8) ◽  
pp. 3941-3949 ◽  
Author(s):  
Wil H. F. Goessens ◽  
Akke K. van der Bij ◽  
Ria van Boxtel ◽  
Johann D. D. Pitout ◽  
Peter van Ulsen ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Membrane Permeability ◽  
Outer Membrane ◽  
Carbapenem Resistance ◽  
Covalent Modification ◽  
Content Type ◽  
E Coli ◽  
Outer Membrane Permeability

ABSTRACTA liver transplant patient was admitted with cholangitis, for which meropenem therapy was started. Initial cultures showed a carbapenem-susceptible (CS)Escherichia colistrain, but during admission, a carbapenem-resistant (CR)E. colistrain was isolated. Analysis of the outer membrane protein profiles showed that both CS and CRE. colilacked the porins OmpF and OmpC. Furthermore, PCR and sequence analysis revealed that both CS and CRE. colipossessedblaCTX-M-15andblaOXA-1. The CRE. colistrain additionally harboredblaCMY-2and demonstrated a >15-fold increase in β-lactamase activity against nitrocefin, but no hydrolysis of meropenem was detected. However, nitrocefin hydrolysis appeared strongly inhibited by meropenem. Furthermore, the CMY-2 enzyme demonstrated lower electrophoretic mobility after its incubation eitherin vitroorin vivowith meropenem, indicative of its covalent modification with meropenem. The presence of the acyl-enzyme complex was confirmed by mass spectrometry. By transformation of the CMY-2-encoding plasmid into variousE. colistrains, it was established that both porin deficiency and high-level expression of the enzyme were needed to confer meropenem resistance. In conclusion, carbapenem resistance emerged by a combination of elevated β-lactamase production and lack of porin expression. Due to the reduced outer membrane permeability, only small amounts of meropenem can enter the periplasm, where they are trapped but not degraded by the large amount of the β-lactamase. This study, therefore, provides evidence that the mechanism of “trapping” by CMY-2 β-lactamase plays a role in carbapenem resistance.

scholarly journals Effects of Multiple Deletions of Murein Hydrolases on Viability, Septum Cleavage, and Sensitivity to Large Toxic Molecules in Escherichia coli

2002 ◽  
Vol 184 (22) ◽  
pp. 6093-6099 ◽  
Author(s):  
Christoph Heidrich ◽  
Astrid Ursinus ◽  
Jürgen Berger ◽  
Heinz Schwarz ◽  
Joachim-Volker Höltje
Keyword(s):  
Escherichia Coli ◽  
Molecular Weight ◽  
Membrane Permeability ◽  
Outer Membrane ◽  
High Molecular Weight ◽  
Macconkey Agar ◽  
Lytic Transglycosylases ◽  
E Coli ◽  
Murein Hydrolase ◽  
Outer Membrane Permeability

ABSTRACT The multiplicity of murein hydrolases found in most bacteria presents an obstacle to demonstrating the necessity of these potentially autolytic enzymes. Therefore, Escherichia coli mutants with deletions in multiple murein hydrolases, including lytic transglycosylases, amidases, and dd-endopeptidases, were constructed. Even a mutant from which seven different hydrolases were deleted was viable and grew at a normal rate. However, penicillin-induced lysis was retarded. Most of the mutants were affected in septum cleavage, which resulted in the formation of chains of cells. All three enzymes were shown to be capable of splitting the septum. Failure to cleave the septum resulted in an increase in outer membrane permeability, and thus the murein hydrolase mutants did not grow on MacConkey agar plates. In addition, the hydrolase mutants not only could be lysed by lysozyme in the absence of EDTA but also were sensitive to high-molecular-weight antibiotics, such as vancomycin and bacitracin, which are normally ineffective against E. coli.

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