A nanomechanical study of the effects of colistin on the Klebsiella pneumoniae AJ218 capsule

Anna Mularski, Jonathan Wilksch, Eric Hanssen, Jian Li, Takehiro Tomita, Sacha James Pidot, Tim Stinear, Frances Separovic, Dick Strugnell

Research output: Contribution to journalArticleResearchpeer-review

2 Citations (Scopus)

Abstract

Atomic force microscopy measurements of capsule thickness revealed that that the wild-type Klebsiella pneumoniae AJ218 capsular polysaccharides were rearranged by exposure to colistin. The increase in capsule thickness measured near minimum inhibitory/bactericidal concentration (MIC/MBC) is consistent with the idea that colistin displaces the divalent cations that cross-bridge adjacent lipopolysaccharide (LPS) molecules through the capsule network. Cryo-electron microscopy demonstrated that the measured capsule thickness at near MIC/MBC of 1.2 μM was inflated by the disrupted outer membrane, through which the capsule is excreted and LPS is bound. Since wild-type and capsule-deficient strains of K. pneumoniae AJ218 have equivalent MICs and MBCs, the presence of the capsule appeared to confer no protection against colistin in AJ218. A spontaneously arising colistin mutant showed a tenfold increase in resistance to colistin; genetic analysis identified a single amino acid substitution (Q95P) in the PmrB sensor kinase in this colistin-resistant K. pneumoniae AJ218. Modification of the lipid A component of the LPS could result in a reduction of the net-negative charge of the outer membrane, which could hinder binding of colistin to the outer membrane and displacement of the divalent cations that bridge adjacent LPS molecules throughout the capsular polysaccharide network. Retention of the cross-linking divalent cations may explain why measurements of capsule thickness did not change significantly in the colistin-resistant strain after colistin exposure. These results contrast with those for other K. pneumoniae strains that suggest that the capsule confers colistin resistance.

Original languageEnglish
Pages (from-to)351-361
Number of pages11
JournalEuropean Biophysics Journal
Volume46
Issue number4
DOIs
Publication statusPublished - 1 May 2017

Keywords

  • Antimicrobial peptide
  • Atomic force microscopy
  • Capsular polysaccharide
  • Colistin
  • Klebsiella pneumoniae
  • Polymyxin

Cite this

Mularski, Anna ; Wilksch, Jonathan ; Hanssen, Eric ; Li, Jian ; Tomita, Takehiro ; Pidot, Sacha James ; Stinear, Tim ; Separovic, Frances ; Strugnell, Dick. / A nanomechanical study of the effects of colistin on the Klebsiella pneumoniae AJ218 capsule. In: European Biophysics Journal. 2017 ; Vol. 46, No. 4. pp. 351-361.
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Mularski, A, Wilksch, J, Hanssen, E, Li, J, Tomita, T, Pidot, SJ, Stinear, T, Separovic, F & Strugnell, D 2017, 'A nanomechanical study of the effects of colistin on the Klebsiella pneumoniae AJ218 capsule', European Biophysics Journal, vol. 46, no. 4, pp. 351-361. https://doi.org/10.1007/s00249-016-1178-2

A nanomechanical study of the effects of colistin on the Klebsiella pneumoniae AJ218 capsule. / Mularski, Anna; Wilksch, Jonathan; Hanssen, Eric; Li, Jian; Tomita, Takehiro; Pidot, Sacha James; Stinear, Tim; Separovic, Frances; Strugnell, Dick.

In: European Biophysics Journal, Vol. 46, No. 4, 01.05.2017, p. 351-361.

Research output: Contribution to journalArticleResearchpeer-review

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AU - Wilksch, Jonathan

AU - Hanssen, Eric

AU - Li, Jian

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AB - Atomic force microscopy measurements of capsule thickness revealed that that the wild-type Klebsiella pneumoniae AJ218 capsular polysaccharides were rearranged by exposure to colistin. The increase in capsule thickness measured near minimum inhibitory/bactericidal concentration (MIC/MBC) is consistent with the idea that colistin displaces the divalent cations that cross-bridge adjacent lipopolysaccharide (LPS) molecules through the capsule network. Cryo-electron microscopy demonstrated that the measured capsule thickness at near MIC/MBC of 1.2 μM was inflated by the disrupted outer membrane, through which the capsule is excreted and LPS is bound. Since wild-type and capsule-deficient strains of K. pneumoniae AJ218 have equivalent MICs and MBCs, the presence of the capsule appeared to confer no protection against colistin in AJ218. A spontaneously arising colistin mutant showed a tenfold increase in resistance to colistin; genetic analysis identified a single amino acid substitution (Q95P) in the PmrB sensor kinase in this colistin-resistant K. pneumoniae AJ218. Modification of the lipid A component of the LPS could result in a reduction of the net-negative charge of the outer membrane, which could hinder binding of colistin to the outer membrane and displacement of the divalent cations that bridge adjacent LPS molecules throughout the capsular polysaccharide network. Retention of the cross-linking divalent cations may explain why measurements of capsule thickness did not change significantly in the colistin-resistant strain after colistin exposure. These results contrast with those for other K. pneumoniae strains that suggest that the capsule confers colistin resistance.

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KW - Atomic force microscopy

KW - Capsular polysaccharide

KW - Colistin

KW - Klebsiella pneumoniae

KW - Polymyxin

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