Rapid in vitro conversion and identification of Coccidioides immitis

Since many contaminating nonpathogenic fungi resemble Coccidioides immitis culturally, isolates from patients must be inoculated into laboratory animals to confirem identification as C. immitis. This procedure is time-consuming, expensive, and not generally available in clinical laboratories. When cultures of C. immitis were grown in slide cultures on modified Converse liquid medium in purified agar and incubated at 40 C in a candle jar, all 57 isolates demonstrated inhibition of mycelial growth and conversion of arthrospores to endosporulating spherules in 3 to 5 days. Representative isolates of six species of nonpathogenic fungi that resembled C. immitis culturally either did not grow or failed to produce endosporulating spherules under the same conditions. This procedure is recommended for confirming the identication of a culture as C. immitis.