Pythium destruens sp. nov., an agent of equine pythiosis.

The equine phycomycotic agent known commonly as Hyphomyces destruens or occasionally as Pythium gracile, is described as a new species Pythium destruens. Separation is on the basis of morphological features, temperature growth profiles, esterase/lipase activity, and carbohydrate utilization ability. P. diclinum (synonymous with P. gracile sensu Middleton) showed minor differences in vesicle, oospore and oogonium size from P. destruens. P. destruens grew at 40 degrees C on corn meal agar and hydrolysed esters of lauric and oleic acids. These abilities were not displayed by P. diclinum, but this species grew more vigorously on cellobiose, fructose, gentibiose, inulin, raffinose, maltose, mannose, salicin, starch and sucrose than P. destruens. The latter species showed no substantial ability for growth on inulin, raffinose, and salicin. Equine isolates from Australia, Japan and New Guinea were similar.