Misidentification of Aspergillus nomius and Aspergillus tamarii as Aspergillus flavus: characterization by internal transcribed spacer, β-Tubulin, and calmodulin gene sequencing, metabolic fingerprinting, and matrix-assisted laser desorption ionization-time of flight mass spectrometry.
Aspergillus nomius and Aspergillus tamarii are Aspergillus species that phenotypically resemble Aspergillus flavus. In the last decade, a number of case reports have identified A. nomius and A. tamarii as causes of human infections. In this study, using an internal transcribed spacer, β-tubulin, and calmodulin gene sequencing, only 8 of 11 clinical isolates reported as A. flavus in our clinical microbiology laboratory by phenotypic methods were identified as A. flavus. The other three isolates were A. nomius (n = 2) or A. tamarii (n = 1). The results corresponded with those of metabolic fingerprinting, in which the A. flavus, A. nomius, and A. tamarii strains were separated into three clusters based on ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC MS) analysis. The first two patients with A. nomius infections had invasive aspergillosis and chronic cavitary and fibrosing pulmonary and pleural aspergillosis, respectively, whereas the third patient had A. tamarii colonization of the airway. Identification of the 11 clinical isolates and three reference strains by matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) showed that only six of the nine strains of A. flavus were identified correctly. None of the strains of A. nomius and A. tamarii was correctly identified. β-Tubulin or the calmodulin gene should be the gene target of choice for identifying A. flavus, A. nomius, and A. tamarii. To improve the usefulness of MALDI-TOF MS, the number of strains for each species in MALDI-TOF MS databases should be expanded to cover intraspecies variability.
Department of Microbiology, The University of Hong Kong, Pokfulam, Hong Kong.
Emily W T
EW
Tam
Jonathan H K
JH
Chen
Eunice C L
EC
Lau
Antonio H Y
AH
Ngan
Kitty S C
KS
Fung
Kim-Chung
KC
Lee
Ching-Wan
CW
Lam
Kwok-Yung
KY
Yuen
Susanna K P
SK
Lau
Patrick C Y
PC
Woo
D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001228:Aspergillosis / Q000382:microbiology*; D001230:Aspergillus / Q000737:chemistry / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification; D002147:Calmodulin / Q000235:genetics; D016000:Cluster Analysis; D004271:DNA, Fungal / Q000737:chemistry / Q000235:genetics; D018509:DNA, Helminth / Q000737:chemistry / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000737:chemistry / Q000235:genetics; D005260:Female; D006801:Humans; D008297:Male; D055442:Metabolome; D008828:Microbiological Techniques / Q000379:methods*; D008875:Middle Aged; D008969:Molecular Sequence Data; D010802:Phylogeny; D017422:Sequence Analysis, DNA; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; D014404:Tubulin / Q000235:genetics
D002147:Calmodulin; D004271:DNA, Fungal; D018509:DNA, Helminth; D021903:DNA, Ribosomal Spacer; D014404:Tubulin