Classification of the dermatophytes, a group of keratinophilic
fungi, depends primarily on morphological criteria, but individual
identification is often difficult. Many species have been created,
based on what are often minor differences in structure or unacceptable
characters such as isolation from different hosts or different clinical
conditions.
Biochemical techniques, used successfully in the differentiation
of other micro-organisms, have had a limited application in the study
of dermatophytes and were made the subject of special investigation. 22
species were grown on media containing 30 different carbon or nitrogen
sources. It was found that both geophilic and zoophilic species had
similar nutritional patterns, but for some, e. g. Microsporumýypseuxn and
Trhyton mentagrophytes, nutritional and biochemical tests are of
little taxonomic value. Ability to hydrolyse urea allows differentiation
of T. mentagrophytes from T. rubrum and T. erinacei, and T. soudanense
from M. ferrugineum. Other nutritional differences which may be used
to separate species are described. The results obtained are complementary
to the classification of dermatophytes based on morphological criteria
but do support the separation of certain species, e.. a. M. equinum, hitherto
regarded as variants of another species.
Serological investigations are described and five groups have
been established, based on the presence or absence of common antigens.
The results show that the genus Microsporum, with the exception of
M. gypseum and M. persicolor, is serologically distinct from the genus
Trichophyton. M. gypseum, T. ajelloi and M. persicolor are
serologically related, however, having common antigens. The genus
Trichophyton was found to contain two serological sub-groups:
(1) T. mentagrophytes-T. rubrum-T. schoenleinii, and (2) T. quinckeanum-
T. soudanense-T. erinacei. T. tonsurans has close relationships with
most other Trichophyton species. T. violaceum and Epidermophyton floccosum
had few antigens in common with any other species. The two saprophytic
species, T. terrestre and M. cookei, appeared to be serologically unrelated
to other members of the respective genera.