Direct detection of Histoplasma capsulatum in soil suspensions by two-stage PCR.

Histoplasmosis is the most common pulmonary mycosis in the United States. The responsible fungal pathogen, Histoplasma capsulatum, grows in soils contaminated with bird or bat droppings. Inhalation of dust from contaminated areas containing H. capsulatum spores is a primary route of infection. The ability to detect H. capsulatum in soil samples has been limited by the lack of fast, reliable and inexpensive methods. A polymerase chain reaction (PCR) method was developed that allows the direct detection of H. capsulatum in soil. A two-stage PCR protocol was followed employing both fungal-specific primers and nested primers specific for the internal transcribed spacer (ITS) region of the 5.8S rRNA gene of H. capsulatum. The estimated limit of detection of this method is 10 spores. In contrast to the more expensive and indirect mouse inoculum assay, which requires 6-8 weeks for sample analysis, PCR analysis of soil contaminated with H. capsulatum can be completed in less than 2 days.