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Rapid identification of capsulated Acinetobacter baumannii using a density-dependent gradient test

Authors
  • Kon, Hadas1
  • Schwartz, David1
  • Temkin, Elizabeth1
  • Carmeli, Yehuda1, 2
  • Lellouche, Jonathan1
  • 1 Tel-Aviv Sourasky Medical Center, 6 Weizmann St, Tel-Aviv, 6423906, Israel , Tel-Aviv (Israel)
  • 2 Tel-Aviv University, Tel-Aviv, Israel , Tel-Aviv (Israel)
Type
Published Article
Journal
BMC Microbiology
Publisher
Springer (Biomed Central Ltd.)
Publication Date
Sep 16, 2020
Volume
20
Issue
1
Identifiers
DOI: 10.1186/s12866-020-01971-9
Source
Springer Nature
Keywords
License
Green

Abstract

BackgroundGram-negative bacterial capsules are associated with production of carbohydrates, frequently resulting in a mucoid phenotype. Infections caused by capsulated or mucoid A. baumannii are associated with increased clinical severity. Therefore, it is clinically and epidemiologically important to identify capsulated A. baumannii. Here, we describe a density-dependent gradient test to distinguish between capsulated and thin/non-capsulated A. baumannii.ResultsThirty-one of 57 A. baumannii isolates displayed a mucoid phenotype. The density-dependent gradient test was comprised of two phases, with silica concentrations of 30% (top phase) and 50% (bottom phase). Twenty-three isolates migrated to the bottom phase, indicating thin or non-capsulated strains, and 34 migrated to the top phase, suggesting strains suspected to be capsulated. There was agreement between the mucoid and the non-mucoid phenotypes and the density-dependent gradient test for all but three isolates. Total carbohydrates extracted from strains suspected to be capsulated were significantly higher. Transmission electron microscopy confirmed the presence of a capsule in the six representative strains suspected to be capsulated.ConclusionsThe density-dependent gradient test can be used to verify capsule presence in mucoid-appearing A. baumannii strains. Identifying capsulated strains can be useful for directing infection control measures to reduce the spread of hypervirulent strains.

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