Page 161 - Ebook-Book JCMS 2025

The Role of Intracellular Conditions in Transition of Thermally
Dimorphic Talaromyces marneffei
Sriwarom A1, Boonchird K2, Vijitjammaree T2, Suchartlikitwong P3,4, Meesilpavikkai K3*
1 Medical Microbiology, Interdisciplinary Program, Graduate School, Chulalongkorn University
2 Doctor of Medicine Program, Faculty of Medicine, Chulalongkorn University
3 Department of Microbiology, Faculty of Medicine, Chulalongkorn University
4 Division of Infectious Diseases, Department of Medicine, Faculty of Medicine, Chulalongkorn University
*Corresponding Author E-mail: kornvalee.m@chula.md
Background: Abstract
Talaromyces marneffei, thermally dimorphic fungi, causes invasive fungal infections in
immunocompromised individuals in endemic areas. It typically exhibits a mold form at
25°C in the environment and transitions to a pathogenic yeast form at 37°C within the host.
Despite exposure to 37°C, T. marneffei cultured in hemoculture bottles often displays mold
instead of the yeast form.
Objectives: Methods: This study investigates whether the morphological transformation of T. marneffei
depends on intracellular conditions and whether the hyphal transformation observed in the
hemoculture system results from cell lytic agents in hemoculture bottles routinely used in
hospitals.
THP-1 human monocytic cells were co-incubated with T. marneffei conidia to study intracellular
transformation into yeast/mold forms. Saponin and cytochalasin D (a phagocytosis inhibitor)
were used to confirm extracellular yeast and conidia transformations. To mimic the routine
hemoculture system, conidial suspension, macrophage-phagocytosed conidia, and yeast were
injected into hemoculture bottles and incubated at 37°C in an automated hemoculture system.
Results: Conclusion: After two days of co-incubation with THP-1 cells, T. marneffei conidia were phagocytosed
and transformed into yeast cells. When saponin, a cell lytic agent, was added, macrophage-
containing yeast cells were lysed, releasing yeasts into the supernatant, and complete
transformation into mold was observed after four days. In the control condition, THP-1
treated with cytochalasin D revealed hyphal transformation without the yeast phase. To
simulate the hemoculture process, conidia, macrophage-phagocytosed conidia, and
macrophage-phagocytosed yeast were injected into hemoculture bottles and incubated at
37°C. After positive signals were detected, hyphal forms were found in all conditions.
Both temperature and intracellular conditions influence the morphology of T. marneffei.
It is crucial for medical practitioners not to overlook the possibility of the mold form of
T. marneffei when culturing in hemoculture bottles.
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