Hyaline Hyphomycetes include those conidial fungi which are not darkly pigmented, colonies may be colorless or brightly colored. These include the agents of hyalohyphomycosis, Aspergillosis, dermatophytosis and the dimorphic pathogens, like Histoplasma capsulatum. Descriptions of the following genera are avaiable:
Identification of the hyphomycetes is primarily based on microscopic morphology including; (a) conidial morphology, especially septation, shape, size, color and cell wall texture; (b) the arrangement of conidia as they are borne on the conidiogenous cells, for example are they solitary, arthrocatenate, blastocatenate, basocatenate or gloiosporae etc., (c) the type conidiogenous cell, for example non-specialized or hypha-like, phialide, annellide or sympodial etc., and (d) other additional features such as the presence of sporodochia or synnemata.
Culture characteristics, although less reliable may also be useful. These include surface texture, topography and pigmentation, reverse pigmentation and growth at 37C. For identification, potato dextrose agar and cornmeal agar are two of the most suitable media to use and exposure to daylight is recommended to maximize culture color characteristics.
Key Features include Microscopic Morphology and Culture Characteristics:
Mandatory to see conidial characteristics to make an identification therefore you must have a good slide preparation [needle mounts, tape mounts, slide cultures]. May also need to stimulate sporulation by using different media, such as potato dextrose agar or cornmeal agar. If conidia are present then assess the following characters:
1. Conidial characteristics:
- Septation [amero, didymo, phragmo, dictyo].
- Shape [spherical, subspherical, pyriform, clavate, ellipsoidal etc].
- Size [need graduated eye piece, <10 mm etc].
- Colour [hyaline or darkly pigmented].
- Wall texture [smooth, rough, verrucose, echinulate etc].
- How many conidial types present? [micro and macro].
2. Arrangement of conidia as they are borne on the conidiogenous cells.
- Solitary [single, in balls, acropleurogenous].
- Catenulate [acropetal or basipetal].
- Botryose [synchronous or asynchronous].
3. Growth of the conidiogenous cell.
- Proliferous [basauxic, percurrent or sympodial (narrow or broad base)].
4. Type of conidiogenous cell present.
5. Any additional features present.
- Origin of conidium wall [holoblastic or enteroblastic].
- Hyphal structures [clamps, spirals, nodular organs etc].
- Synnemata, Sporodochia, Chlamydoconidia, Pycnidia etc.
6. Culture Characteristics. Least reliable as the media and growth conditions play an important part. Examine the following characteristics:
- Surface texture [glabrous, suede-like, powdery, granular, fluffy, downy, cottony etc].
- Surface topography [flat, raised, heaped, folded, domed, radial grooved].
- Surface pigmentation [white, cream, yellow, brown, green, grey, black etc].
- Reverse pigmentation [none, yellow, brown, red etc].
- Growth rate [eg colonies growing less than 5 mm in 14 days etc].
- Growth temperature studies are also often very useful [37C, 40C & 45C].