Differences in virulence of Sporothrix schenckii conidia related to culture conditions and cell-wall components

A murine model was used to evaluate the virulence of Sporothrix schenckii c onidia cultured for 4, 7, 10 or 12 days in Sabouraud's dextrose broth (SDB) , A correlation was observed between length of culture and virulence. Mice infected intravenously with S, schenckii conidia cultured for 4 or 7 days s howed 40-100% cumulative mortality, In contrast, mice infected with conidia from cultures grown for 10 or 12 days in SDB showed no mortality (100% sur vival). A much greater accumulation of fungal colony forming units (cfu) wa s observed in the lungs, livers and spleens of mice inoculated with conidia of S, schenckii cultured for 7 days than in mice infected with conidia cul tured for 12 days. The livers of mice from the former group showed a widesp read granulomatous reaction whereas mice inoculated,vith S, schenckii cultu red for 12 days showed a more limited response with fewer granulomas, No di fference in viability or replicative capacity was discerned for these S, sc henckii cultured cells. However, the more virulent forms of the fungus show ed differences in cell-wall sugar composition with rhamnose:mannose molar r atios of 1.7:1.0 for cells cultured for 4 days and 1.0:1.7 for conidia cult ured for 12 days. These results suggest that the virulence of S, schenckii conidia may be determined by their cell-wall composition.