Potassium Tellurite and Copper Sulphate in Sabouraud's Medium for Isolation of Pathogenic Fungi

In the isolation of pathogenic fungi, one of the principal difficulties is the occurrence of bacterial contamination. This is particularly true when dealing with scales and crusts which are usually loaded with saprophytic bacteria. In trying to overcome this difficulty we have found potassium tellurite and copper sulphate to be of value as by incorporating them into Sabouraud's medium they are found to be capable of suppressing the growth of bacteria but not that of fungi. In reviewing the literature, we have been able to find few reports in which chemicals were incorporated in Sabouraud's medium for the inhibition of contaminants. Sauthof 1 found that with stock cultures, 1-2% of yatren in Sabouraud's medium was able to inhibit the growth of staphylococcus but not of fungi. In our study the experimental material was taken directly from lesions of fungous infections since it seemed more practical to work with actual specimens than with stock cultures. The details of this study are presented below.

Different concentrations of potassium tellurite and copper sulphate were incorporated into Sabourand's medium on which materials such as hairs, scales, and crusts taken directly from lesions of known fungous infection were heavily inoculated. Plain Sabouraud's glucose-agar was used as control. The inoculated tubes were kept at room-temperature and observations were frequently made. The suitable concentrations of these (chemicals in Sabouraud's medium for this work were found to be 0.015% and 0.05% for potassium tellurite and copper sulphate respectively. The results of the culture are presented in Table I.

Besides the data presented it may be mentioned that the fungi isolated in this study were Trichophyton violaceum, Microsporon ferrugineum, Achorion schönleini, Epidemophyton rubrum, and Epidermophyton inguinale. It was noted that Achorion schönleini from favus scutala was more resistant and could stand a higher concentration of the chemicals than the others. On the Sabouraud's medium with 0.02% of potassium tellurite, the isolation of Achorion schönleini from favus scutala was usually quite easy while with the same medium, the growth of other species from hairs or scales was frequently retarded. With copper sulphate, the Achorion schönleini could grow very well in a concentration of 0.06% while the others were found to grow best in the concentrations of from 0.04 to 0.05%.