title: Matrix-assisted laser desorption ionization time-of-flight mass spectrometry for rapid identification of mold and yeast cultures of Penicillium marneffei.
abstract: BACKGROUND
  Penicillium marneffei is the most important thermal dimorphic fungus causing systemic mycosis in HIV-infected and other immunocompromised patients in Southeast Asia. However, laboratory diagnosis of penicilliosis, which relies on microscopic morphology and mycelial-to-yeast conversion, is time-consuming and expertise-dependent, thus delaying diagnosis and treatment. Although matrix -assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is useful for identification of various medically important fungi, its performance for identification of P. marneffei is less clear.
  
  
  RESULTS
  We evaluated the performance of the Bruker MALDI-TOF MS system for identification of mold and yeast cultures of 59 clinical strains and the type strain of P. marneffei using the direct transfer method, with results compared to four phylogenetically closely related species, P. brevi-compactum, P. chrysogenum, Talaromyces aurantiacus and T. stipitatus. Using the Bruker original database combined with BDAL v4.0.0.1 and Filamentous Fungi Library 1.0, MALDI-TOF MS failed to identify the 60 P. marneffei strains grown in mold and yeast phase (identified as P. funiculosum and P. purpurogenum with scores <1.7 respectively). However, when the combined database was expanded with inclusion of spectra from 21 P. marneffei strains in mold and/or yeast phase, all the remaining 39 P. marneffei strains grown in mold or phase were correctly identified to the species level with score >2.0. The MS spectra of P. marneffei exhibited significant difference to those of P. brevi-compactum, P. chrysogenum, T. aurantiacus and T. stipitatus. However, MALDI-TOF MS failed to identify these four fungi to the species level using the combined database with or without spectra from P. marneffei.
  
  
  CONCLUSIONS
  MALDI-TOF MS is useful for rapid identification of both yeast and mold cultures of P. marneffei and differentiation from related species. However, accurate identification to the species level requires database expansion using P. marneffei strains.
authors.affiliation: State Key Laboratory of Emerging Infectious Diseases, The University of Hong Kong, Hong Kong, China. skplau@hkucc.hku.hk.|Research Centre of Infection and Immunology, The University of Hong Kong, University Pathology Building, Queen Mary Hospital, Hong Kong, China. skplau@hkucc.hku.hk.|Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, China. skplau@hkucc.hku.hk.|Department of Microbiology, The University of Hong Kong, Hong Kong, China. skplau@hkucc.hku.hk.
authors.forename: Susanna K P
authors.initials: SK
authors.lastname: Lau
authors.affiliation: Hong Kong Sanatorium Hospital, Hong Kong, China.
authors.forename: Clare S K
authors.initials: CS
authors.lastname: Lam
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Antonio H Y
authors.initials: AH
authors.lastname: Ngan
authors.affiliation: Department of Microbiology, The University of Hong Kong, Hong Kong, China.
authors.forename: Wang-Ngai
authors.initials: WN
authors.lastname: Chow
authors.affiliation: Department of Pathology, Pamela Youde Nethersole Eastern Hospital, Hong Kong, China.
authors.forename: Alan K L
authors.initials: AK
authors.lastname: Wu
authors.affiliation: Department of Pathology, Queen Elizabeth Hospital, Hong Kong, China.
authors.forename: Dominic N C
authors.initials: DN
authors.lastname: Tsang
authors.affiliation: Department of Pathology, Kwong Wah Hospital, Hong Kong, China.
authors.forename: Cindy W S
authors.initials: CW
authors.lastname: Tse
authors.affiliation: Department of Pathology, Tuen Mun Hospital, Hong Kong, China.
authors.forename: Tak-Lun
authors.initials: TL
authors.lastname: Que
authors.affiliation: Hong Kong Sanatorium Hospital, Hong Kong, China.
authors.forename: Bone S F
authors.initials: BS
authors.lastname: Tang
authors.affiliation: State Key Laboratory of Emerging Infectious Diseases, The University of Hong Kong, Hong Kong, China. pcywoo@hkucc.hku.hk.|Research Centre of Infection and Immunology, The University of Hong Kong, University Pathology Building, Queen Mary Hospital, Hong Kong, China. pcywoo@hkucc.hku.hk.|Carol Yu Centre for Infection, The University of Hong Kong, Hong Kong, China. pcywoo@hkucc.hku.hk.|Department of Microbiology, The University of Hong Kong, Hong Kong, China. pcywoo@hkucc.hku.hk.
authors.forename: Patrick C Y
authors.initials: PC
authors.lastname: Woo
mesh_terms: D005658:Fungi / Q000737:chemistry / Q000145:classification / Q000302:isolation & purification; D006801:Humans; D016533:Mycological Typing Techniques / Q000379:methods*; D009181:Mycoses / Q000382:microbiology*; D010407:Penicillium / Q000737:chemistry* / Q000302:isolation & purification*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*
keywords: Identification; MALDI-TOF; MS; Pencillium; Rapid; marneffei