scholarly journals A pmrA Constitutive Mutant Sensitizes Escherichia coli to Deoxycholic Acid

2006 ◽  
Vol 188 (3) ◽  
pp. 1180-1183 ◽  
Author(s):  
Jamie M. Froelich ◽  
Khoa Tran ◽  
Daniel Wall
Keyword(s):  
Escherichia Coli ◽  
Sequence Analysis ◽  
Outer Membrane ◽  
Missense Mutation ◽  
Lipid A ◽  
Deoxycholic Acid ◽  
Barrier Properties ◽  
Polymyxin B ◽  
Iron And Zinc ◽  
Constitutive Mutant

ABSTRACT An Escherichia coli mutant was isolated and shown to be polymyxin B resistant. Mapping and sequence analysis revealed a missense mutation at codon 53 within the pmrA (basR) gene that results in a G-to-V substitution. Fusions of promoters from the pmrC, yibD, and pmrH genes with the lacZ reporter showed that they were constitutively expressed in pmrA53 cells. In pmrA + strains, these promoters were induced by iron and zinc, while a ΔpmrA mutation blocked induction. The PmrA regulon regulates genes whose products remodel the composition and charge of lipid A and hence the barrier properties of the outer membrane. Along these lines, the pmrA53 mutant was also found to be hypersensitive to the anionic bile detergent deoxycholic acid.

scholarly journals Antibiotic-Mediated Modulations of Outer Membrane Vesicles in Enterohemorrhagic Escherichia coli O104:H4 and O157:H7

2017 ◽  
Vol 61 (9) ◽  
Author(s):  
Andreas Bauwens ◽  
Lisa Kunsmann ◽  
Helge Karch ◽  
Alexander Mellmann ◽  
Martina Bielaszewska
Keyword(s):  
Escherichia Coli ◽  
Outer Membrane ◽  
Shiga Toxin ◽  
Membrane Vesicles ◽  
Polymyxin B ◽  
Outer Membrane Vesicles ◽  
Enterohemorrhagic Escherichia Coli ◽  
Content Type ◽  
E Coli ◽  
Major Virulence Factor

ABSTRACT Ciprofloxacin, meropenem, fosfomycin, and polymyxin B strongly increase production of outer membrane vesicles (OMVs) in Escherichia coli O104:H4 and O157:H7. Ciprofloxacin also upregulates OMV-associated Shiga toxin 2a, the major virulence factor of these pathogens, whereas the other antibiotics increase OMV production without the toxin. These two effects might worsen the clinical outcome of infections caused by Shiga toxin-producing E. coli. Our data support the existing recommendations to avoid antibiotics for treatment of these infections.

scholarly journals Yersinia pestis Is Viable with Endotoxin Composed of Only Lipid A

2005 ◽  
Vol 187 (18) ◽  
pp. 6599-6600 ◽  
Author(s):  
Li Tan ◽  
Creg Darby
Keyword(s):  
Escherichia Coli ◽  
Yersinia Pestis ◽  
Outer Membrane ◽  
Salmonella Enterica ◽  
Lipid A ◽  
Gram Negative Bacteria ◽  
Membrane Component ◽  
Gram Negative ◽  
Serovar Typhimurium

ABSTRACT Lipopolysaccharide (LPS) is the major outer membrane component of gram-negative bacteria. The minimal LPS structure for viability of Escherichia coli and Salmonella enterica serovar Typhimurium is lipid A glycosylated with 3-deoxy-D-manno-octulosonic acid (Kdo) residues. Here we show that another member of the Enterobacteriaceae, Yersinia pestis, can survive without Kdo in its LPS.

scholarly journals Structure and Association of Human Lactoferrin Peptides with Escherichia coli Lipopolysaccharide

2004 ◽  
Vol 48 (6) ◽  
pp. 2190-2198 ◽  
Author(s):  
Daniel S. Chapple ◽  
Rohanah Hussain ◽  
Christopher L. Joannou ◽  
Robert E. W. Hancock ◽  
Edward Odell ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Outer Membrane ◽  
Bactericidal Activity ◽  
Membrane Surface ◽  
Polymyxin B ◽  
Cd Spectroscopy ◽  
Time Dependent ◽  
Human Lactoferrin ◽  
Lag Phase ◽  
Ligand Interaction

ABSTRACT An 11-amino-acid amphipathic synthetic peptide homologous to a helical region on helix 1 of human lactoferrin HLP-2 exhibited bactericidal activity against Escherichia coli serotype O111, whereas an analogue synthesized with Pro substituted for Met, HLP-6, had greatly reduced antimicrobial activity. The bactericidal activity of HLP-2 was 10-fold greater than that of HLP-6 in both buffer and growth medium by time-kill assays. These assays also showed a pronounced lag phase that was both concentration and time dependent and that was far greater for HLP-2 than for HLP-6. Both peptides, however, were shown to be equally efficient in destabilizing the outer membrane when the hydrophobic probe 1-N-phenylnaphthylamine was used and to have the same lipopolysaccharide (LPS) binding affinity, as shown by polymyxin B displacement. Circular dichroism (CD) spectroscopy was used to study the structure and the organization of the peptides in solution and upon interaction with E. coli LPS. In the presence of LPS, HLP-2 and HLP-6 were found to bind and adopt a β-strand conformation rather than an α-helix, as shown by nonimmobilized ligand interaction assay-CD spectroscopy. Furthermore, this assay was used to show that there is a time-dependent association of peptide that results in an ordered formation of peptide aggregates. The rate of interpeptide association was far greater in HLP-2 LPS than in HLP-6 LPS, which was consistent with the lag phase observed on the killing curves. These results allow us to propose a mechanism by which HLP-2 folds and self-assembles at the outer membrane surface before exerting its activity.

scholarly journals Biological Characterization of Endotoxins Released from Antibiotic-Treated Pseudomonas aeruginosa and Escherichia coli

1998 ◽  
Vol 42 (5) ◽  
pp. 1015-1021 ◽  
Author(s):  
Teruo Kirikae ◽  
Fumiko Kirikae ◽  
Shinji Saito ◽  
Kaoru Tominaga ◽  
Hirohi Tamura ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Pseudomonas Aeruginosa ◽  
Lipid A ◽  
Biological Activities ◽  
Polymyxin B ◽  
Mitogen Activated Protein Kinase ◽  
No Production ◽  
Endotoxic Activity

ABSTRACT The supernatants taken from Pseudomonas aeruginosa andEscherichia coli cultures in human sera or chemically defined M9 medium in the presence of ceftazidime (CAZ) contained high levels of endotoxin, while those taken from the same cultures in the presence of imipenem (IPM) yielded a very low level of endotoxin. The biological activities of endotoxin in the supernatants were compared with those of phenol water-extracted lipopolysaccharide (LPS). The endotoxin released from the organisms as a result of CAZ treatment (CAZ-released endotoxin) contained a large amount of protein. The protein, however, lacked endotoxic activity, since the endotoxin did not show any in vivo toxic effects in LPS-hyporesponsive C3H/HeJ mice sensitized with d-(+)-galactosamine (GalN) or any activation of C3H/HeJ mouse macrophages in vitro. The activities of CAZ- and IPM-released endotoxin (as assessed by a chromogenicLimulus test) were fundamentally the same as those ofP. aeruginosa LPS, since their regression lines were parallel. The CAZ-released endotoxin was similar to purified LPS with respect to the following biological activities in LPS-responsive C3H/HeN mice and LPS-hyporesponsive C3H/HeJ mice: lethal toxicity in GalN-sensitized mice, in vitro induction of tumor necrosis factor- and NO production by macrophages, and mitogen-activated protein kinase activation in macrophages. The macrophage activation by CAZ-released endotoxin as well as LPS was mainly dependent on the presence of serum factor and CD14 antigen. Polymyxin B blocked the activity. These findings indicate that the endotoxic activity of CAZ-released endotoxin is due primarily to LPS (lipid A).

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 Interactions of polymyxin B in combination with aztreonam, minocycline, meropenem and rifampicin against Escherichia coli producing NDM and OXA-48-group carbapenemases

2021 ◽  
Author(s):  
Anna Olsson ◽  
Marcus Hong ◽  
Hissa Al-Farsi ◽  
Christian G. Giske ◽  
Pernilla Lagerbäck ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Lipid A ◽  
Time Lapse ◽  
Polymyxin B ◽  
Positive Interactions ◽  
Exact Test ◽  
E Coli ◽  
Genes Encoding ◽  
Severe Infections

Objectives. Carbapenemase-producing Enterobacterales pose an increasing medical threat. Combination therapy is often used for severe infections; however, there is little evidence supporting the optimal selection of drugs. This study aimed to determine the in vitro effects of polymyxin B combinations against carbapenemase-producing Escherichia coli . Methods. The interactions of polymyxin B in combination with aztreonam, meropenem, minocycline or rifampicin against 20 clinical isolates of NDM and OXA-48-group-producing E. coli were evaluated using time-lapse microscopy. 24-h samples were spotted on plates with and without 4 x MIC polymyxin B for viable counts. Whole-genome sequencing was applied to identify resistance genes and mutations. Finally, potential associations between combination effects and bacterial genotypes were assessed using Fisher’s exact test. Results. Synergistic and bactericidal effects were observed with polymyxin B and minocycline against 11/20 strains and with polymyxin B and rifampicin against 9/20 strains. The combinations of polymyxin B and aztreonam or meropenem showed synergy against 2/20 strains. Negligible resistance development against polymyxin B was detected. Synergy with polymyxin B and minocycline was associated with genes involved in efflux (presence of tet(B) , wildtype soxR and the marB mutation H44Q) and lipopolysaccharide synthesis ( eptA C27Y, lpxB mutations and lpxK L323S). Synergy with polymyxin B and rifampicin was associated with sequence variations in arnT , which plays a role in lipid A modification. Conclusion. Polymyxin B in combination with minocycline or rifampicin frequently showed positive interactions against NDM- and OXA-48-group-producing E. coli . Synergy was associated with genes encoding efflux and components of the bacterial outer membrane.

Sequence analysis of mutations that prevent export of λ receptor, an Escherichia coli outer membrane protein

Nature ◽  
1980 ◽  
Vol 285 (5760) ◽  
pp. 82-85 ◽  
Author(s):  
Scott D. Emr ◽  
Joe Hedgpeth ◽  
Jean-Marie Clément ◽  
Thomas J. Silhavy ◽  
Maurice Hofnung
Keyword(s):  
Escherichia Coli ◽  
Sequence Analysis ◽  
Membrane Protein ◽  
Outer Membrane ◽  
Outer Membrane Protein

scholarly journals LpxT-Dependent Phosphorylation of Lipid A in Escherichia coli Increases Resistance to Deoxycholate and Enhances Gut Colonization

2021 ◽  
Vol 12 ◽  
Author(s):  
Xudong Tian ◽  
Guillaume Manat ◽  
Elise Gasiorowski ◽  
Rodolphe Auger ◽  
Samia Hicham ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Cell Surface ◽  
Lipid A ◽  
Negative Charge ◽  
Polymyxin B ◽  
Gram Negative Bacteria ◽  
Bacterial Cells ◽  
Gram Negative ◽  
E Coli ◽  
Gut Colonization

The cell surface of Gram-negative bacteria usually exhibits a net negative charge mostly conferred by lipopolysaccharides (LPS). This property sensitizes bacterial cells to cationic antimicrobial peptides, such as polymyxin B, by favoring their binding to the cell surface. Gram-negative bacteria can modify their surface to counteract these compounds such as the decoration of their LPS by positively charged groups. For example, in Escherichia coli and Salmonella, EptA and ArnT add amine-containing groups to the lipid A moiety. In contrast, LpxT enhances the net negative charge by catalyzing the synthesis of tri-phosphorylated lipid A, whose function is yet unknown. Here, we report that E. coli has the intrinsic ability to resist polymyxin B upon the simultaneous activation of the two component regulatory systems PhoPQ and PmrAB by intricate environmental cues. Among many LPS modifications, only EptA- and ArnT-dependent decorations were required for polymyxin B resistance. Conversely, the acquisition of polymyxin B resistance compromised the innate resistance of E. coli to deoxycholate, a major component of bile. The inhibition of LpxT by PmrR, under PmrAB-inducing conditions, specifically accounted for the acquired susceptibility to deoxycholate. We also report that the kinetics of intestinal colonization by the E. coli lpxT mutant was impaired as compared to wild-type in a mouse model of infection and that lpxT was upregulated at the temperature of the host. Together, these findings highlight an important function of LpxT and suggest that a tight equilibrium between EptA- and LpxT-dependent decorations, which occur at the same position of lipid A, is critical for the life style of E. coli.

scholarly journals Phosphate Groups of Lipid A Are Essential for Salmonella enterica Serovar Typhimurium Virulence and Affect Innate and Adaptive Immunity

2012 ◽  
Vol 80 (9) ◽  
pp. 3215-3224 ◽  
Author(s):  
Qingke Kong ◽  
David A. Six ◽  
Qing Liu ◽  
Lillian Gu ◽  
Shifeng Wang ◽  
...  
Keyword(s):  
Outer Membrane ◽  
Adaptive Immunity ◽  
Salmonella Enterica ◽  
Lipid A ◽  
Outer Membrane Proteins ◽  
Polymyxin B ◽  
Content Type ◽  
Serovar Typhimurium ◽  
Phosphate Groups

ABSTRACTLipid A is a key component of the outer membrane of Gram-negative bacteria and stimulates proinflammatory responses via the Toll-like receptor 4 (TLR4)-MD2-CD14 pathway. Its endotoxic activity depends on the number and length of acyl chains and its phosphorylation state. InSalmonella entericaserovar Typhimurium, removal of the secondary laurate or myristate chain in lipid A results in bacterial attenuation and growth defectsin vitro. However, the roles of the two lipid A phosphate groups in bacterial virulence and immunogenicity remain unknown. Here, we used anS. TyphimuriummsbB pagL pagP lpxRmutant, carrying penta-acylated lipid A, as the parent strain to construct a series of mutants synthesizing 1-dephosphorylated, 4′-dephosphorylated, or nonphosphorylated penta-acylated lipid A. Dephosphorylated mutants exhibited increased sensitivity to deoxycholate and showed increased resistance to polymyxin B. Removal of both phosphate groups severely attenuated the mutants when administered orally to BALB/c mice, but the mutants colonized the lymphatic tissues and were sufficiently immunogenic to protect the host from challenge with wild-typeS. Typhimurium. Mice receivingS. Typhimurium with 1-dephosphorylated or nonphosphorylated penta-acylated lipid A exhibited reduced levels of cytokines. Attenuated and dephosphorylatedSalmonellavaccines were able to induce adaptive immunity against heterologous (PspA ofStreptococcus pneumoniae) and homologous antigens (lipopolysaccharide [LPS] and outer membrane proteins [OMPs]).

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