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Malassezia restricta: An Underdiagnosed Causative Agent of Blood Culture-Negative Infective Endocarditis

Linda Houhamdi Hammou1, Yvonne Benito1, André Boibieux2

  • 1Laboratoire de Bactériologie. Institut des Agents Infectieux. Hôpital de la Croix Rousse, Hospices Civils de Lyon, Lyon, France.

Clinical Infectious Diseases : an Official Publication of the Infectious Diseases Society of America
|May 19, 2021
PubMed
Abstract

Insights

An ultra-sensitive molecular technique successfully identified the cause of infective endocarditis (IE) in all microbiologically nondocumented cases. Malassezia restricta, a fungus resistant to common treatments, was identified as an underestimated IE agent.

Area of Science:

  • Infectious Diseases
  • Microbiology
  • Molecular Diagnostics

Background:

  • Infective endocarditis (IE) is a serious condition where identifying the causative microorganism is crucial for effective treatment.
  • A significant percentage of IE cases (5.2%) remain microbiologically undiagnosed using conventional methods.
  • Current diagnostic limitations necessitate improved techniques for identifying pathogens in IE.

Purpose of the Study:

  • To enhance the diagnosis of IE by employing an ultra-sensitive molecular method.
  • To investigate microbiologically nondocumented IE (NDIE) cases using advanced molecular techniques on cardiac samples.
  • To identify etiological agents in IE cases that were negative by culture and conventional PCR.

Main Methods:

  • Retrospective analysis of cardiac samples from patients with definite IE over a 5-year period.
  • Definition of NDIE based on Duke criteria with negative cultures, bacterial amplification, and serologies.
  • Application of an ultra-sensitive molecular diagnostic kit (Universal Microbe Detection) for microbial DNA detection.
  • Fungal identification confirmed via 26S-rDNA and internal transcribed spacer amplifications, histology, and serological assays.

Main Results:

  • Microbial DNA was detected in all 16 NDIE cases analyzed.
  • Typical bacterial IE pathogens were identified in 13 cases.
  • Malassezia restricta was identified in the remaining 3 NDIE cases, confirmed by histological and serological analyses.

Conclusions:

  • Malassezia restricta is an underrecognized cause of NDIE.
  • Serological cross-reactivity between M. restricta and Candida albicans can lead to misdiagnosis.
  • The intrinsic resistance of M. restricta to echinocandins highlights the clinical significance of accurate identification.
Keywords:
Malassezia restrictablood culture-negative endocarditisfungal endocarditisinfective endocarditismolecular biology

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