Effect of Relative Humidity on Gross Morphology of Certain Pathogenic Fungi. ∗

Abstract

In this study the effect of relative humidity under controlled air velocity and temperature on gross morphology of certain pathogenic fungi is determined.

It has been shown that ratio of constituents of mediums 1 and availability of oxygen 2 influence colony morphology. Variation in microscopic morphology with change in humidity has been studied repeatedly 3 but gross morphological changes under conditions such as used have not been recorded.

With high humidity one expects a less powerful nutrient gradient to the surface and a lesser tendency to surface growth and with low humidity the reverse. Such variation exists in nature in regions where there are deep and shallow root vegetation. 4

To study the effect of humidity, organisms were grown on a medium producing a predominantly subsurface growth (1% d-glutamic acid, 4% dextrose, 1½% agar, pH 5.6) 5 and one producing a predominantly surface growth (Sabouraud's proof medium—1% peptone, 4% dextrose, 1½% agar, pH 5.6).

Cabinets† used for growth were placed in a room having a refrigeration control set at 70°F. An 80% relative humidity was obtained by circulating in a scrubbing tower through which air passed to the cabinets a saturated technical sodium chloride solution and a 97% by substituting tap water. Air velocity was set at 6 ft./min.

The following pathogenic fungi and 2 nonpathogenic saprophytes, Lichthemia sp. and Scopulariopsis brevicaulis, were studied: Achorion schoenleinii, Acladium castellani, Candida Candida, Endodermophyton indicum, E. tropicale, Endomyces capsulatus, E. dermatitidus, Epidermophyton cruris, E. inguinale, E. rubrum, Glenospora Gammeli, Geotrichum Bachmann, Indiella americana, Microsporon Audouini, M. felineum, M. gypseum, Monosporium apiospermum, Monilia albicans, Oospora humi, Sporotrichum Schenckii, Trichophyton balcaneum, T. crateriforme, T. decalvans, T. granulosum, T. gypseum, T. gypseum-asteroides, T. gypseum-lacticolor, T. interdigitale, T. louisianicum, T. niveum, T. purpureum, T. sulfureum, Willia anomala. Observations were made on growths kept in the cabinets 30 days.