10 



CULTIVATION AND GROWTH 



sorbose, by a more colonial and less rapid growth on agar (293). The 

 growing hyphal tips are killed and new branches then form and grow 

 laterally (181). 



4. DIMORPHISM 



Several fungi pathogenic to man are found in infected tissues in a 

 unicellular yeastlike form, but when cultivated at room temperature 

 grow out in a mycelial form. The term dimorphism strictly applies to 

 these forms only, but related phenomena in the normally filamentous 

 fungi may provisionally be considered as in the same category. A 

 dimorphic fungus is one, therefore, in which a reversible transforma- 

 tion from a mycelial to a non-mycelial and unicellular growth type 

 occurs. 



Dimorphism is common in the yeasts (262), and unicellular bacteria 

 may be caused experimentally to form filaments by, for example, 

 magnesium deficiency (216, 326). Some normally filamentous fungi, 

 e.g., smut fungi, grow in culture as unicellular budding cells. The 

 fungi listed in Table 1 include both the pathogenic dimorphic fungi 



Table 1. Factors Affecting Non-mycelial Growth in Fungi 



Organism 

 Candida albicans, C. tropicahs 



Blastomyces dermatitidis 



Histoplasma capsulatum 

 Histoplasma farciminosum 

 Paracoccidioides brasiliensis 

 Sporotrichum schencki 

 Trichosporon capitatum 

 Ceratostomella ulmi 

 Dematium pullulans 

 Fusarium oxysporumf. nicotianae 

 Mucor guillermondii 

 Ophiostoma multiannulatum 

 Romano a terricola 



Non-mycelial Phase Favored by 



Cysteine, NH 4 C1, glucose carbon source (152, 



211, 214, 217) 

 High temperature (35-37°C) cultivation (177, 



256) 

 Cysteine, high temperature (255) 

 High C0 2 (40) 



High temperature (37°C) cultivation (82, 256) 

 HighC0 2 (81, 254) 

 Cysteine (217) 

 Aeration (75), low pH (26) 

 Low aeration (11), low carbohydrate (263) 

 Aeration (339) 

 Low aeration (186) 

 High (12 mg per liter) inositol (107) 

 Aeration (299) 



and those filamentous fungi in which production of a unicellular 

 growth phase can be induced reversibly. It should be stressed that in 

 this second group the morphology of the unicellular phase may not be 

 the same for all forms listed; i.e., the available information does not 

 discriminate between, say, conidia and hyphal fragments. The diver- 



