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 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.

Activity of Goats' Milk Lactoperoxidase System on Pseudomonas fluorescens and Escherichia coli at Refrigeration Temperatures

1995 ◽  
Vol 58 (10) ◽  
pp. 1136-1138 ◽  
Author(s):  
PALOMA ZAPICO ◽  
PILAR GAYA ◽  
MANUEL NUÑEZ ◽  
MARGARITA MEDINA
Keyword(s):  
Escherichia Coli ◽  
Pseudomonas Fluorescens ◽  
Bactericidal Activity ◽  
Inhibitory Activity ◽  
Initial Level ◽  
Lag Phase ◽  
E Coli ◽  
Lactoperoxidase System ◽  
System Activation ◽  
Control Milk

Bactericidal activity of the lactoperoxidase (LP) system against Pseudomonas fluorescens was observed in refrigerated raw goats' milk. Mean decreases in the levels of P. fluorescens of 1.69 log units at 4°C and 1.85 log units at 8°C were achieved during the first 24 h by LP-system activation. Inhibitory activity depended on temperature and length of incubation. P. fluorescens counts lower than the initial level were recorded in activated LP-system milk for 5 days at 4°C and 3 days at 8°C. Escherichia coli did not grow in raw goats' milk at 4°C, and the influence of LP-system activation at this temperature on E. coli counts was negligible. At 8°C, E. coli was able to grow in control milk with no apparent lag phase. In contrast, a lag phase of 2 days was observed in activated LP-system milk at 8°C, resulting in lower E. coli counts than those of control milk during the first 5 days.

scholarly journals Plasmid-determined resistance to serum bactericidal activity: a major outer membrane protein, the traT gene product, is responsible for plasmid-specified serum resistance in Escherichia coli

1980 ◽  
Vol 28 (2) ◽  
pp. 359-367 ◽  
Author(s):  
A Moll ◽  
P A Manning ◽  
K N Timmis
Keyword(s):  
Escherichia Coli ◽  
Outer Membrane ◽  
Gene Product ◽  
Bactericidal Activity ◽  
Transfer Functions ◽  
Rabbit Serum ◽  
Insertion Mutant ◽  
Serum Resistance ◽  
Major Structural Component ◽  
Mutant Derivative

Resistance to the bactericidal activity of serum appears to be an important virulence property of invasive bacteria. The conjugative multiple-antibiotic-resistance plasmid R6-5 was found to confer upon Escherichia coli host bacteria increased resistance against rabbit serum. Gene-cloning techniques were used to localize the serum resistance determinant of R6-5 to a segment of the plasmid that encodes conjugal transfer functions, and a pACYC184 hybrid plasmid, designated pKT107, that contains this segment was constructed. The generation and analysis of deletion and insertion mutant derivatives of the pKT107 plasmid that no longer specify serum resistance permitted precise localization of the serum-resistance cistron on the R6-5 map and demonstrated that this locus is coincident with that of traT, one of the two surface exclusion genes of R6-5. Examination of the proteins synthesized in E. coli minicells of pKT107 and its serum-sensitive mutant derivative plasmids confirmed that the serum-resistance gene product of R6-5 is the traT protein and showed that this protein is a major structural component (about 21,000 copies per cell) of the bacterial outer membrane.

High-resolution, low-dose electron cryomicroscopy of sugar embedded porin, a transmembrane protein from Eschrichia coli outer membrane

1987 ◽  
Vol 45 ◽  
pp. 790-791
Author(s):  
H. J. Sass ◽  
A. Massalski ◽  
F. Zemlin ◽  
E. Beckman ◽  
M. van Heel ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Outer Membrane ◽  
Low Dose ◽  
Quaternary Structure ◽  
Transmembrane Protein ◽  
Membrane Surface ◽  
Electron Cryomicroscopy ◽  
Hydrophobic Residues ◽  
Voltage Dependent ◽  
Hydrophilic Residues

The secondary structure of porin, which form voltage-dependent channels across outer membrane of Escherichia coli, consists mostly (two-thirds of polypeptides) of anti-parallel (β-pleated strands. However, information on the tertiary and quaternary structure of porin is still far from complete. The β-pleated strands, which have a mean length of 10-12 residues, span the outer membrane in an orientation approximately perpendicular to the membrane surface. Porins are so far the only class of membrane proteins for which the predominant β-structure has been established unequivocally. However, the exact arrangement of β-strands (β- barrels or stacked sheets) is still unknown. Depending on the method of investigation, one being the turn identification, and the second the Raman spectroscopy, 16 or 18 β-strands respectively were calculated as a building block required for one protein monomer. Both models predict the β-strands delineating the pore, as amphipatic molecules with hydrophobic residues forming protein-lipid interface and hydrophilic residues facing the lumen of the pore.

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 Evaluating Polymyxin B-Based Combinations against Carbapenem-Resistant Escherichia coli in Time-Kill Studies and in a Hollow-Fiber Infection Model

2016 ◽  
Vol 61 (1) ◽  
Author(s):  
Yiying Cai ◽  
Tze-Peng Lim ◽  
Jocelyn Qi-Min Teo ◽  
Suranthran Sasikala ◽  
Eric Chun Yong Chan ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Growth Rate ◽  
Bactericidal Activity ◽  
Hollow Fiber ◽  
Polymyxin B ◽  
Phenotypic Characterization ◽  
Infection Model ◽  
Content Type ◽  
Carbapenem Resistant ◽  
Time Kill

ABSTRACT Polymyxin B-based combinations have emerged as a mainstay treatment against carbapenem-resistant Escherichia coli (CREC). We investigated the activity of polymyxin B-based two-antibiotic combinations against CREC using time-kill studies (TKS) and validated the findings in a hollow-fiber infection model (HFIM). TKS were conducted using 5 clinical CREC strains at 5 log10 CFU/ml against 10 polymyxin B-based two-antibiotic combinations at maximum clinically achievable concentrations. HFIMs simulating dosing regimens with polymyxin B (30,000U/kg/day) and tigecycline (100 mg every 12 h) alone and in combination were conducted against two CREC strains at 5 log10 CFU/ml over 120 h. Emergence of resistance was quantified using antibiotic-containing media. Phenotypic characterization (growth rate and stability of resistant phenotypes) of the resistant isolates was performed. All five CREC strains harbored carbapenemases. Polymyxin B and tigecycline MICs ranged from 0.5 mg/liter to 2 mg/liter and from 0.25 mg/liter to 8 mg/liter, respectively. All antibiotics alone did not have bactericidal activity at 24 h in the TKS, except for polymyxin B against two strains. In combination TKS, only polymyxin B plus tigecycline demonstrated both bactericidal activity and synergy in two out of five strains. In the HFIM, polymyxin B alone was bactericidal against both CREC strains before regrowth was observed at 8 h. Phenotypically stable polymyxin B-resistant mutants were observed for both strains, with a reduced growth rate observed in one strain. Tigecycline alone resulted in a slow reduction in bacterial counts. Polymyxin B plus tigecycline resulted in rapid and sustained bactericidal killing up to 120 h. Polymyxin B plus tigecycline is a promising combination against CREC. The clinical relevance of our results warrants further investigations.

scholarly journals Direct Observation of Conversion From Walled Cells to Wall-Deficient L-Form and Vice Versa in Escherichia coli Indicates the Essentiality of the Outer Membrane for Proliferation of L-Form Cells

2021 ◽  
Vol 12 ◽  
Author(s):  
Taiki Chikada ◽  
Tomomi Kanai ◽  
Masafumi Hayashi ◽  
Taishi Kasai ◽  
Taku Oshima ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Outer Membrane ◽  
Polymyxin B ◽  
Cell Deformation ◽  
Gram Negative Bacteria ◽  
Physical Force ◽  
Synthesis Inhibitor ◽  
Hypertonic Medium ◽  
Gram Negative ◽  
E Coli

Gram-negative bacteria such as Escherichia coli are surrounded by an outer membrane, which encloses a peptidoglycan layer. Even if thinner than in many Gram-positive bacteria, the peptidoglycan in E. coli allows cells to withstand turgor pressure in hypotonic medium. In hypertonic medium, E. coli treated with a cell wall synthesis inhibitor such as penicillin G form wall-deficient cells. These so-called L-form cells grow well under anaerobic conditions (i.e., in the absence of oxidative stress), becoming deformed and dividing as L-form. Upon removal of the inhibitor, they return to the walled rod-shaped state. Recently, the outer membrane was reported to provide rigidity to Gram-negative bacteria and to strengthen wall-deficient cells. However, it remains unclear why L-form cells need the outer membrane for growth. Using a microfluidic system, we found that, upon treatment with the outer membrane-disrupting drugs polymyxin B and polymyxin B nonapeptide or with the outer membrane synthesis inhibitor CHIR-090, the cells lysed during cell deformation and division, indicating that the outer membrane was important even in hypertonic medium. L-form cells could return to rod-shaped when trapped in a narrow space, but not in a wide space, likely due to insufficient physical force. Outer membrane rigidity could be compromised by lack of outer membrane proteins; Lpp, OmpA, or Pal. Deletion of lpp caused cells to lyse during cell deformation and cell division. In contrast, ompA and pal mutants could be deformed and return to small oval cells even when less physical force was exerted. These results strongly suggest that wall-deficient E. coli cells require a rigid outer membrane to survive, but not too rigid to prevent them from changing cell shape.

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