Gram-negative

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Pseudomonas aeruginosa Gram negative bacteria.jpg
The gram-negative bacterial cell walls are one of the two types of bacterial cell walls which can be identified by the Gram stain test. After the Gram stain test Gram-negative bacteria appear red or pink when observed under the microscope as they do not retain the crystal violet dye after rinsing and red safranin dye enters the cell wall when counterstaining all due to thin peptidoglycan layer.

Gram-negative bacteria include Haemophilus influenzae, Escherichia coli[1] and other bacteria.

Contents

Cell wall structure of the Gram-negative bacteria

The cell envelope of Gram-negative bacteria contains two membranes (outer membrane and inner (cell) membrane). In-between these membranes lies a thin peptidoglycan layer and the aqueous periplasm where various nutrient-transporting enzymes and transporters are found. The outer membrane of Gram-negative cell walls is porous to ions, contains toxic lipid parts of lipopolysaccharides[2] and has defensive properties[3].

Characteristics

Infections caused by Gram-negative bacteria and treatment implications

Gram-negative bacteria cause such infections as pneumonia and septicaemia[4]. Gram-negative bacterial cell walls are more complex than Gram-positive bacterial cell walls as the former possess two membranes and their outer membrane contains porin proteins that limit the size of molecules entering the cell, therefore, preventing large quantities of antibiotics from entering the cell wall where they would take effect[5]. As many antibiotics inhibit enzymes important in the assembly of peptidoglycan layer which in Gram-negative bacteria lies between two membranes, many antibiotics that are effective against Gram-positive bacteria are ineffective against Gram-negative bacteria as they cannot go through the outer membrane and access the peptidoglycan layer inside the cell envelope[6].

References

  1. Walsh C. Antibiotics: actions, origins, resistance. Washington: ASM Press. 2003
  2. Reece JB et al. Campbell Biology. 9th ed. San Francisco: Pearson Education Inc. 2011
  3. Slonczewski J, Foster JW. Microbiology: an evolving science. 4th ed. New York: W. W. Norton & Company. 2016
  4. Walsh C. Antibiotics: actions, origins, resistance. Washington: ASM Press. 2003
  5. Walsh C. Antibiotics: actions, origins, resistance. Washington: ASM Press. 2003
  6. Walsh C. Antibiotics: actions, origins, resistance. Washington: ASM Press. 2003

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