First report of urease activity in the novel systemic fungal pathogen Emergomyces africanus: a comparison with the neurotrope Cryptococcus neoformans

Barbra Lerm, Chris Kenyon, Ilan S Schwartz, Heinrich Kroukamp, Riaan de Witt, Nelesh P Govender, G Sybren de Hoog, Alfred Botha

Research output: Contribution to journalA1: Web of Science-article

Abstract

Cryptococcus neoformans is an opportunistic pathogen responsible for the AIDS-defining illness, cryptococcal meningitis. During the disease process, entry of cryptococcal cells into the brain is facilitated by virulence factors that include urease enzyme activity. A novel species of an Emmonsia-like fungus, recently named Emergomyces africanus, was identified as a cause of disseminated mycosis in HIV-infected persons in South Africa. However, in contrast to C. neoformans, the enzymes produced by this fungus, some of which may be involved in pathogenesis, have not been described. Using a clinical isolate of C. neoformans as a reference, the study aim was to confirm, characterise and quantify urease activity in E. africanus clinical isolates. Urease activity was tested using Christensen's urea agar, after which the presence of a urease gene in the genome of E. africanus was confirmed using gene sequence analysis. Subsequent evaluation of colorimetric enzyme assay data, using Michaelis-Menten enzyme kinetics, revealed similarities between the substrate affinity of the urease enzyme produced by E. africanus (Km ca. 26.0 mM) and that of C. neoformans (Km ca. 20.6 mM). However, the addition of 2.5 g/l urea to the culture medium stimulated urease activity of E. africanus, whereas nutrient limitation notably increased cryptococcal urease activity.

Original languageEnglish
JournalFEMS Yeast Research
Volume17
Issue number7
Pages (from-to)fox069
ISSN1567-1356
DOIs
Publication statusPublished - 2017

Keywords

  • Journal Article

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