Mycopathologia 112: 157-163, 1990. 9 1990KluwerAcademicPublishers. Printedin Belgium.

The growth of Epidermophyton floccosum and E. stockdaleae at different temperatures F.J. Cabafies, M a R. Bragulat, T. Bruguera & L. Abarca Departamento de Patolog/a y Producciones Animales (Microbiologia) Facultad de Veterinaria. Universidad Autdnoma de Barcelona, 08193 Bellaterra, Barcelona, Espa~a Received 10 October 1989; accepted in revised form 18 March 1990

Key words: Epidermophyton floccosum, E. stockdaleae, growth, incubation temperature

Abstract

The ability of 17 strains of genus Epidermophyton (15 strains belonging to Epidermophyton floccosum, one to E. floccosum var. nigricans and one to E. stockdaleae) to grow at different temperatures (4 ~C, 25 ~C, 28 ~ 31 ~ 34 ~ 37 ~ and 40 ~ was stated. The strains were inoculated on Sabouraud Dextrose Agar and regularly controled over a period of 14 days when the plates were incubated at 25 ~ 28 ~ 31 ~ 34 ~ 37 ~ and 40 ~ and over a period of 70 days when the temperature was 4 ~ The optimal growth ofE. floccosum was observed at 28 ~ and 31 ~ and no signs of growth were recorded neither at 4 ~ nor at 40 ~ The optimal development ofE. stockdaleae was observed at 25 ~ and 28 ~ This species grew from 4 ~ to 31 ~

Introduction

At a given thermic level, the aspect of the colonies as well as the shape and size of the microscopic structures depend on the culture medium, the incubation time, the strain, and in particular, on the optimal and maximum temperatures [10]. Only two species are included in the genus Epidermophyton. Epidermophyton floccosum (Harz) Langeron & Milochevitch 1930 is categorized as anthropophilic species and regularly responsible for a small percentage of tinea cruris, tinea pedis, tinea corporis and onychomycosis [9], although their occasional occurence in animals has been described [2, 5, 11]. This species type includes a variety E. floccosum var. nigricans [4], with a characteristic dark pigment diffusing into the surrounding agar. The second species is Epidermophyton stock-

daleae. It is categorized as geophilic species and it so far has not mentioned as being a causal agent of dermatomycosis. There is only one isolation of this species described by Prochacki and Engelhardt-Zasada [7]. The ability of 17 strains of genus Epidermophyton to grow at different temperatures (4 ~ 25 ~ 28 ~ 31 ~ 34 ~ 37 ~ and 40 ~ was stated in the present study.

Methods

Strains used. Seventeen strains of genus Epidermophyton were included in the investigation: 14 strains of E. floccosum provided by spanish hospitals, E. floccosum ATCC E18397, E. floccosum var. nigricans ATCC 26072 and E. stockdaleae ATCC 28687.

158 Inoculation technique and incubation temperatures tested. To perform this study, the strains were inoculated in 9 cm Petri dishes containing 25 ml of Sabouraud Dextrose Agar (Difco) following the three-point technique [6, 8] which is as follows: Inoculum was prepared by growing the strains on Sabouraud Dextrose Agar tubes at 28 ~ for seven days. Spore suspensions of each strain were made in aqueous solution of 0.0001~o Tween 80. Selected positions on the agar surface were spot inoculated with a loop of the suspension to obtain three-point cultures. The cultures were regularly controled over a period of 14 days when the plates were incubated at25 ~ 28 ~ 31 ~ 30 ~ 37 ~ ~ and over a period of 70 days when the temperature was 4 ~C.

Results and discussion

The results belonging to the growth rate obtained from this study are summarized in the Figs. 1, 2 and 3, and in Table 1. The Fig. 1 shows the variation in the diameter of the colonies of E. stockdaleae throughout the incubation period at 4 ~C. This strain was the only one that grew at 4 oC. The variation in the diameter of the colonies of all the strains studied at 25 ~ 28 ~ 31 ~ 34 ~ and 37 ~ at 7 and 14 days of incubation is given in Fig. 2.

Cultural characteristics studied. The rate of colony growth was calculated at least on six replicates of each strain for each temperatures. Two diameters, measured in each colony at right angles to one another, were averaged to give the mean diameter for each colony. Other macroscopic features as colour of surface and reverse, texture, concentric and radial grooves, odour, exudate, pigment diffusing into the surrounding agar medium (P.D.) and microscopic characteristics as presence of macroconidia and chlamydospores were recorded.

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The growth of Epidermophyton floccosum and E. stockdaleae at different temperatures.

The ability of 17 strains of genus Epidermophyton (15 strains belonging to Epidermophyton floccosum, one to E. floccosum var. nigricans and one to E. ...
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