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Morphologic and physiologic studies of three dematiaceous pathogens
Abstract:
Uncertainty in identifying a dematiaceous mold from a human bronchial washing precipitated a study of Dactylaria gallopava (Cooke) Bhatt et Kendrick and its relationship to Scolecobasidium constrictum Abbott. Morphologic and physiologic studies were conducted with representative isolates and subcultures derived from the isolates used to prepare the type specimens of these two fungi, as well as a third dark mold, Ochroconis constricta (Abbott) de Hoog et von Arx. All test isolates were morphologically similar in that two-celled, cylindrical blastoconidia with a rhexolytic mode of dehiscence were the predominant and most consistent anamorphic structures. Sympodial development of the conidiophore was too variable to distinguish the isolates. Based on their morphologic similarity, we propose a new combination within the genus Dactylaria as amended by Bhatt and Kendrick, D. constricta (Abbott) Dixon et Salkin. However, D. constricta could be differentiated into two groups on the basis of physiologic tests--a subgroup in which isolates grow at 37 and 45 degrees C, give a delayed positive gelatin reaction, and are inhibited on Mycosel agar; and a second subgroup in which isolates grow on Mycosel agar and give a rapid positive gelatin reaction, but do not grow at 37 or 45 degrees C. We recommend that D. constricta be viewed as a potential pathogen when isolated from clinical specimens.
Insights
This study clarifies the identification of dematiaceous molds, proposing Dactylaria constricta as a new combination. Dactylaria constricta exhibits distinct physiologic groups and is a potential pathogen in clinical settings.
Area of Science:
- Medical Mycology
- Fungal Taxonomy
- Clinical Microbiology
Background:
- Uncertainty in identifying dematiaceous molds from human bronchial washings.
- Need to clarify the relationship between Dactylaria gallopava, Scolecobasidium constrictum, and Ochroconis constricta.
Purpose of the Study:
- To investigate the morphologic and physiologic characteristics of specific dark molds.
- To resolve taxonomic ambiguities and propose a new fungal combination.
- To assess the clinical significance of these fungi.
Main Methods:
- Morphologic examination of fungal isolates and type specimens.
- Physiologic testing, including growth at different temperatures and biochemical reactions (gelatin hydrolysis).
- Comparative analysis of anamorphic structures and conidiophore development.
Main Results:
- All tested isolates exhibited similar morphologic features, primarily two-celled, cylindrical blastoconidia.
- Sympodial conidiophore development was not a reliable distinguishing feature.
- Two distinct physiologic subgroups of Dactylaria constricta were identified based on growth at 37/45°C, gelatinase activity, and Mycosel agar growth.
Conclusions:
- A new combination, Dactylaria constricta, is proposed for Scolecobasidium constrictum based on morphologic similarity.
- Physiologic differences differentiate D. constricta into two subgroups.
- Dactylaria constricta should be considered a potential pathogen in clinical specimens.