Histoplasma capsulatum isolates from three St. Louis area AIDS patients with disseminated histoplasmosis were found to be closely related to the temperature-sensitive, previously unique, Downs strain based on growth phenotype and restriction fragment length polymorphisms (RFLP) involving mitochondrial DNA, ribosomal DNA, and the yps-3 gene. H. capsulatum isolates from five non-AIDS patients in the St. Louis area with disseminated histoplasmosis or chronic pulmonary histoplasmosis had the growth phenotype and RFLP pattern characteristic of most strains isolated from other regions of the USA.

We have developed an improved scheme for the classification of environmental and clinical isolates of Histoplasma capsulatum that is based on analysis of mitochondrial DNA (mtDNA) and ribosomal DNA (rDNA). Strains were initially divided into mtDNA groups according to restriction digests of whole-cell DNA and Southern hybridization with cloned mtDNA probes. Strains within a mtDNA class could be further grouped by polymorphisms in rDNA. The majority of soil and clinical isolates from the United States had identical mtDNA patterns; however, rDNA polymorphisms were common in both types of isolates. The combination of mtDNA and rDNA typing described in this report will be useful in resolving questions concerning the epidemiology of H. capsulatum infections.

Using a standard plaque assay and clinical isolates of herpes simplex virus (HSV), we have tested the ability of zinc salts to inactivate HSV. Virus was treated by incubation at 37°C with zinc salts in morpholinepropanesulfonic acid-buffered culture medium and was then diluted and plated onto CV-1 cells for detection and quantitation of remaining infectious virus. Of 10 randomly chosen clinical isolates (five HSV type 1 [HSV-1] isolates and five HSV-2 isolates), seven were inactivated >98% by treatment in vitro with 50 mM zinc gluconate for 2 h and nine were inactivated >97% by treatment with zinc lactate. The effect was concentration dependent. With an HSV-1 isolate, 50 mM zinc gluconate or zinc lactate caused 100% inactivation, 15 mM caused 98 to 99% inactivation, and 5 mM caused 63 to 86% inactivation. With an HSV-2 isolate, 50 and 15 mM zinc gluconate caused 30% inactivation and 5 and 1 mM caused less than 9% inactivation, whereas 50 and 15 mM zinc lactate caused greater than 92% inactivation and 5 and 1 mM caused 37 and 26% inactivation, respectively. The ability of the zinc salts to inactivate HSV was not related to pH in the pH range of 6.1 to 7.6 since inactivation by zinc gluconate or zinc lactate in that pH range was 99.7 to 100% with a 2-h treatment with 50 mM zinc salt. Short (5-min) treatments of selected isolates with zinc gluconate, zinc lactate, zinc acetate, or zinc sulfate yielded inactivation rates of 0 to 55%.

The sulfhydryl blocking agent p-chloromercuriphenylsulfonic acid (PCMS) irreversibly inhibited the mycelium-to-yeast transitions of two virulent strains of Histoplasma capsulatum, G184A and G222B, when the temperature of incubation was 'raised to 37C, and the block persisted even after the cultures were washed free of PCMS. Instead of transforming to yeast cells, PCMS-treatec mycelia continued to grow as mycelia at the elevated temperatures. A less virulent strain (Downs) was more temperature sensitive, but it showed a similar irreversible effect at 34°C. Therefore, the mycelium-to-yeast transition of H. capsulatum is not required for the adaptation of mycelia to elevated temperatures but probably results from the temperature-dependent activation of yeast-specific genes. The transition to yeast is inferred to be obligate for pathogenicity in mice because PCMS-treated mycelia failed to cause infection, and no fungi were seen in tissues after PCMS-treated

LY121019 and amphotericin B were equally active in vitro against most clinical isolates of Candida albicans and Candida tropicalis. Higher concentrations of LY121019 were required for inhibition of Candida glabrata. Other Candida species were inhibited by amphotericin B but not by LY121019.