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

Histoplasmosis is the most common pulmonary mycosis in the United States. T he responsible fungal pathogen, Histoplasma capsulatum, grows in soils cont aminated with bird or bat droppings. Inhalation of dust from contaminated a reas containing H. capsulatum spores is a primary route of infection. The a bility to detect H. capsulatum in soil samples has been limited by the lack of fast, reliable and inexpensive methods. A polymerase chain reaction (PC R) method was developed that allows the direct detection of H. capsulatum i n soil. A two-stage PCR protocol was followed employing both fungal-specifi c 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 an d indirect mouse inoculum assay, wh ich requires 6-8 weeks for sample analy sis, PCR analysis of soil contaminated with H, capsulatum can be completed in less than 2 days.