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

  • Lerm, Barbra1
  • Kenyon, Chris2, 3
  • Schwartz, Ilan S4, 5
  • Kroukamp, Heinrich1
  • de Witt, Riaan1
  • Govender, Nelesh P3, 6
  • de Hoog, G Sybren7
  • Botha, Alfred1
  • 1 Department of Microbiology, Stellenbosch University, Stellenbosch 7602, Western Cape, South Africa. , (South Africa)
  • 2 Sexually Transmitted Infection Unit, Institute of Tropical Medicine, 2000 Antwerp, Belgium. , (Belgium)
  • 3 Department of Medicine, University of Cape Town, Cape Town 7925, Western Cape, South Africa. , (South Africa)
  • 4 Epidemiology for Global Health Institute, Faculty of Medicine and Health Sciences, University of Antwerp, 2000 Antwerp, Belgium. , (Belgium)
  • 5 Rady College of Medicine, Faculty of Health Sciences, University of Manitoba, Winnipeg, MB R3E 3P5, Canada. , (Canada)
  • 6 National Institute for Communicable Diseases, 2131 Johannesburg, South Africa. , (South Africa)
  • 7 CBS-KNAW Fungal Biodiversity Centre, 3508 AD, Utrecht, The Netherlands. , (Netherlands)
Published Article
FEMS Yeast Research
Oxford University Press
Publication Date
Nov 01, 2017
DOI: 10.1093/femsyr/fox069
PMID: 28934415


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.

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