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° 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°C. We recomend that D. constricta be viewed as a potential pathogen when isolated from clinical specimens.