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Related Concept Videos

Formation of Lipopolysaccharides01:19

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Lipopolysaccharides (LPS) are crucial components of the outer membrane of Gram-negative bacteria, serving both structural and functional roles. It contributes to membrane stability and protects bacteria from host immune responses. LPS is composed of three major regions—lipid A, a core oligosaccharide, and an O antigen. The biosynthesis and assembly of LPS involve a highly coordinated set of enzymatic reactions and transport mechanisms. Additionally, LPS is recognized as an endotoxin,...
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The outermost layers of prokaryotic cells play a critical role in their survival, virulence, and interaction with the environment. These layers, often composed of polysaccharides, polypeptides, or proteins, form protective and adhesive structures that vary in organization and function.Capsules and Slime LayersCapsules are highly organized, tightly bound layers that firmly attach to the bacterial cell wall. Capsules are usually made of polysaccharides, though some are made of polypeptides. These...
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Polymorphism refers to the existence of a drug substance in multiple crystalline forms, known as polymorphs. Recently, this term has been expanded to include solvates (forms containing a solvent), amorphous forms (non-crystalline forms), and desolvated solvates (forms from which the solvent has been removed).
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Metabolic activity is crucial for polymyxin B (PmB) antibiotic effectiveness against bacteria like Escherichia coli. Stationary-phase bacteria become tolerant unless metabolically active, revealing a key factor in antibiotic tolerance.

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Area of Science:

  • Microbiology
  • Antibiotic Resistance
  • Bacterial Physiology

Background:

  • Polymyxin antibiotics, including polymyxin B (PmB), target lipopolysaccharides (LPSs) in bacterial membranes.
  • The precise mechanism of bacterial killing by polymyxins remains incompletely understood.

Purpose of the Study:

  • To investigate the role of metabolic activity in polymyxin B lethality.
  • To elucidate the mode of action of polymyxin B in Escherichia coli.

Main Methods:

  • Utilized atomic force microscopy to observe bacterial surface changes.
  • Assessed LPS loss from the outer membrane.
  • Investigated the impact of metabolic state (exponential vs. stationary phase) and nutrient availability on antibiotic efficacy.
  • Examined the effect of the MCR-1 resistance determinant.

Main Results:

  • Polymyxin B lethality against Escherichia coli is dependent on bacterial metabolic activity.
  • Stationary-phase bacteria exhibited tolerance to PmB unless a carbon source was provided.
  • Antibiotic treatment induced outer membrane disruptions and LPS loss, requiring LPS synthesis and transport.
  • The MCR-1 resistance determinant blocked PmB-mediated LPS loss.
  • Outer membrane disruption facilitated PmB entry to the inner membrane, causing cell death via energy-independent permeabilization.

Conclusions:

  • Metabolic activity is essential for polymyxin B's lethal effects.
  • Metabolic inactivity confers tolerance to polymyxin antibiotics.
  • Understanding this mechanism can inform strategies against polymyxin-resistant bacteria.