Deana T. Klein

Morphological response of Trichophyton mentagrophytes to methionine.

SUMMARY Granular cultures of Trichophyton mentagrophytes changed their growth habit when grown on a medium containing, as the source of nitrogen, the 19 L-amino acids found in hydrolysed casein, a response not seen when methionine was omitted. In contrast, pleomorphic cultures of T. mentagrophytes grown on amino acid medium were not modified. The methionine effect has been used successfully to differentiate between normal granular cultures mutant pleomorphic cultures. Also, isolates characterized as atypical pleomorphs could be classified as metabolically granular or pleomorphic.

Time-Temperature Interaction in the Induction of Pleomorphism in Trichophyton mentagrophytes

SUMMARY: The frequency of appearance of mutant pleomorphic patches on the surface growth of granular strains of Trichophyton mentagrophytes was markedly increased by incubation at 36° as compared to the number seen at 26°. A minimum of 8–9 days of incubation at the higher temperature was required to induce the higher frequency of pleomorphic mutants and, as the number of days at 36° increased, the number and relative size of the pleomorphic patches also increased. Typical mutants could be isolated whether the granular culture was incubated for 8–9 or 14 days at 36°. Visual scoring was relatively accurate since most of those patches visually scored as pleomorphic were found on isolation to be typical or atypical mutants. Three phenotypic characters were used here to define pleomorphism: type of surface mycelium, pigmentation on reverse side of colony, and effect of methionine. These characters could change independently of one another. Thus, pleomorphism may be the result of alterations in more than one closely linked chromosome-borne locus.

Interrelation of pH, temperature, and growth in the induction of pleomorphism in Trichophyton mentagrophytes.

There is a paucity of data on the effect of pH on the development of the pleomorphic mutant on the surface of granular strains of dermatophytic fungi, although some work has been reported on the interrelation of pH and growth of various species. Dermatophytic fungi exhibit the ability to grow at pH values of the medium between 4 and 10 (Stockdale, 1953a). An optimum pH for growth of around 6.0 has been reported for Trichophyton tonsurans (Swartz and Georg, 1955) and an optimum of slightly below 7.0 for T. persicolor (Stockdale, 1953b). Dermatophytic fungi also possess the ability to increase the alkalinity of the growth medium, apparently due to the release of ammonia (Georg, 1959). McVeigh and Campbell (1950) found that, when using casein hydrolysate, asparagine, or urea as the nitrogen source, three normal granular strains of T. mentagrophytes changed the pH from around 5.0 to 7.0 in 14 days while three mutant pleomorphic strains did not alter the pH of the growth media. Since the optimum experimental conditions of medium, temperature, and time of incubation required to promote the induction and growth of pleomorphic patches on the mycelium of certain granular strains of T. mentagrophytes are now known (Klein, 1964), the optimum pH for this phenomenon could be ascertained. It is of importance to determine whether there is a positive correlation between mycelial growth capacity and the appearance of pleomorphs. It seemed reasonable that manipulation of the hydrogen ion concentration of the medium might permit an evaluation of this basically important question. This paper, therefore, reports the results of a study on the effects of pH and of temperature on dry weight yield of a typical granular and two typical pleomorphic strains of Trichophyton mentagrophytes (Robin) Blanchard (Klein, 1963) and the relation of pH to the induction and development of the pleomorphic mutant.

Morphological response of Trichophyton mentagrophytes to keratin.

The protein keratin can induce a reversible change in morphology of some granular strains ofTrichophyton mentagrophytes leading to a gross appearance which is indistinguishable from the pleomorphic mutation. The only other chemical which induced the same morphological change was a low concentration of sodium acetate. Pleomorphic cultures ofT. mentagrophytes were unaffected.