Correlation between pathogenicity and temperature sensitivity in different strains of Histoplasma capsulatum.

Abstract

We compared the mycelial to yeast transitions of the Downs strain of Histoplasma capsulatum (low level of virulence) with those of G184A and G222B, two more virulent strains having different levels of pathogenicity for mice. When the morphological transitions are initiated by a temperature shift from 250 to 37°C, all three strains undergo similar physiological changes, but these are less severe in G184A and G222B than in the Downs strain. The transitions from mycelial to yeast morphology in both of the more virulent strains are also one-third more rapid than in Downs. We also find that the differences in temperature sensitivity of the three strains can be correlated with the temperature required for complete uncoupling of oxidative phosphorylation. The differences in sensitivity to elevated temperatures extend to the growth of yeast cells of all three strains.Considered together, our results suggest that sensitivity to elevated temperatures may be a key factor accounting for differences in virulence and that uncoupling of oxidative phosphorylation may be the primary event in the morphological transition in all three strains.

Paracoccidioides brasiliensis: phylogenetic and ecological aspects

“…gatii isolates that do not present satisfactory growth at 37°C are not able to produce fatal infection in rats [23,24]. Lowvirulence isolates of H. capsulatum take a longer time to convert from the mycelial to yeast form than those possessing high virulence [25].…”

Surface Localization of the Yps3p Protein of Histoplasma capsulatum

“…Restriction fragment length polymorphism (RFLP) class 2 strains are the most virulent and thermotolerant and are predominantly North American isolates. In class 2 strains, YPS3 transcription initiates between 2 h and 1 day after a temperature shift from ambient to 37°C and remains continuous during the yeast phase of growth (21,25,34). In RFLP class 3 strains, strains of intermediate virulence and thermotolerance found predominantly in Central and South America, YPS3 transcription is initiated 3 days after a temperature shift, but expression drops off to become undetectable after approximately 12 days (21,25,34).…”

“…In class 2 strains, YPS3 transcription initiates between 2 h and 1 day after a temperature shift from ambient to 37°C and remains continuous during the yeast phase of growth (21,25,34). In RFLP class 3 strains, strains of intermediate virulence and thermotolerance found predominantly in Central and South America, YPS3 transcription is initiated 3 days after a temperature shift, but expression drops off to become undetectable after approximately 12 days (21,25,34). YPS3 is not expressed in RFLP class 1 strains, which are the least virulent and thermotolerant and are geographically widely distributed but have only been found as clinical isolates in severely immunocompromised patients (21,31,34).…”

Adhesion ofHistoplasma capsulatumto pneumocytes and biofilm formation on an abiotic surface

“…However, further studies are needed to better understand the role of this mechanism on the severity and pathogenesis of histoplasmosis. For instance, it would be very interesting to know the association between a strains virulence and biofilm formation, considering that low-virulence strains of H. capsulatum require more time for the mycelium-to-yeast-phase transition at 378C, in contrast to more virulent strains that are capable of resisting temperature changes and transform more quickly to the yeast phase (Medoff et al 1986). This is the first report on H. capsulatum yeast biofilm formation and describes a possible association between the ability of H. capsulatum to form biofilm and the pattern of yeast adhesion to epithelial A549 cells.…”