Soil Isolation and Molecular Identification of Coccidioides immitis

The fungal pathogen Coccidioides immitis, causative agent of coccidioidomycosis or Valley Fever, was first isolated from the environment in 1932. It has been isolated on numerous occasions since then, but always with the use of a mammalian host. The morphology of C. immitis is indistinct from related species, thus, its identification hinges upon its ability to infect and produce spherules in a susceptible animal. In this study, four genetically distinct isolates of C. immitis were isolated from soil samples from the San Joaquin Valley without the use of a host. None of these sites had been definitively associated with human infection. The isolates were identified from over 2400 soil isolates from 720 soil samples using C. immitis specific primers based on the ITS sequence of ribosomal DNA. They were further typed using molecular markers available for clinical isolates of C. immitis.