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High vancomycin MICs within the susceptible range in Staphylococcus aureus bacteraemia isolates are associated with

Rocío Falcón1, Alba Martínez2, Eliseo Albert1

  • 1Microbiology Service, Hospital Clínico Universitario de Valencia, Fundación INCLIVA, Valencia, Spain.

International Journal of Antimicrobial Agents
|April 9, 2016
PubMed

Insights

High vancomycin MICs in Staphylococcus aureus (S. aureus) bloodstream infections correlate with thicker bacterial cell walls. This may explain reduced killing by human immune cells, impacting patient outcomes.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Immunology

Background:

  • Vancomycin minimum inhibitory concentrations (MICs) near the susceptible limit for Staphylococcus aureus (S. aureus) are linked to poor outcomes in bloodstream infections.
  • The precise mechanisms underlying this association require further investigation.

Purpose of the Study:

  • To test if high vancomycin MICs in S. aureus bacteraemia isolates correlate with increased cell wall thickness.
  • To determine if high vancomycin MICs are associated with suboptimal bacterial internalization or lysis by human phagocytes.

Main Methods:

  • Evaluated 95 S. aureus isolates for vancomycin MICs using Etest.
  • Assessed bacterial killing by human phagocytes via a whole blood assay.
  • Investigated bacterial internalization using flow cytometry and cell wall thickness via transmission electron microscopy.

Main Results:

  • Isolates with suboptimal phagocyte killing (<60% killing index) exhibited significantly higher vancomycin MICs (P=0.006).
  • Bacterial cell wall thickness was significantly greater in isolates with lower killing efficiency (P=0.03).
  • Bacterial internalization by neutrophils and monocytes was comparable between groups; no genotypic differences were identified.

Conclusions:

  • High vancomycin MICs in S. aureus bacteraemia are associated with increased cell wall thickness.
  • Thicker cell walls may contribute to reduced intracellular killing by phagocytes, potentially explaining poorer clinical outcomes.
Keywords:
Cell wall thicknessHuman phagocytesIntracellular killingMinimum inhibitory concentration (MIC)Staphylococcus aureusVancomycin

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