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Polymyxins are antibiotics,[1] with a general structure consisting of a cyclic peptide with a long hydrophobic tail. They disrupt the structure of the bacterial cell membrane by interacting with its phospholipids. They are produced by the Gram-positive bacterium Bacillus polymyxa[2] and are selectively toxic for Gram-negative bacteria due to their specificity for the lipopolysaccharide molecule that exists within many Gram-negative outer membranes.

Polymyxins B and E (also known as colistin) are used in the treatment of Gram-negative bacterial infections. The global problem of advancing antimicrobial resistance has led to a renewed interest in their use recently.[3]

Polymyxin M is also known as "mattacin".[4]

Contents

Mechanism of action

After binding to lipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria, polymyxins disrupt both the outer and inner membranes. The hydrophobic tail is important in causing membrane damage, suggesting a detergent-like mode of action.

Removal of the hydrophobic tail of polymyxin B yields polymyxin nonapeptide, which still binds to LPS but no longer kills the bacterial cell. However, it still detectably increases the permeability of the bacterial cell wall to other antibiotics, indicating that it still causes some degree of membrane disorganization.

Gram-negative bacteria can develop resistance to polymyxins through various modifications of the LPS structure that inhibit the binding of polymyxins to LPS.[5]

Clinical use

Polymyxin antibiotics are considered relatively neurotoxic and nephrotoxic[6] and, though effective, are therefore used only if less toxic antibiotics are ineffective or are contraindicated. Typical use cases are infections with strains of Pseudomonas aeruginosa or Enterobacteriaceae species that are highly resistant to other types of antibiotics such as cephalosporins.

Polymyxins are not absorbed from the gastrointestinal tract and therefore must be administered intravenously.

Use in biomedical research

Polymyxins are used to neutralize or absorb LPS contaminating samples that are intended for use in e.g. immunological experiments. Minimization of LPS contamination can be important because LPS can evoke strong reactions from immune cells and therefore distort experimental results.

See also

References

Further reading

  • Giuliani A, Pirri G, Nicoletto S (2007). "Antimicrobial peptides: an overview of a promising class of therapeutics". Cent. Eur. J. Biol. 2 (1): 1–33. doi:10.2478/s11535-007-0010-5.  
  • Pirri G, Giuliani A, Nicoletto S, Pizutto L, Rinaldi A (2009). "Lipopeptides as anti-infectives: a practical perspective". Cent. Eur. J. Biol. 4 (3): 258–273. doi:10.2478/s11535-009-0031-3.  
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