Valley Fever on the Rise—Searching for Microbial Antagonists to the Fungal Pathogen <i>Coccidioides immitis</i>

• Main Authors: Antje Lauer, Joe Darryl Baal, Susan D. Mendes, Kayla Nicole Casimiro, Alyce Kayes Passaglia, Alex Humberto Valenzuela, Gerry Guibert
• Format: Article
• Language: English
• Published: MDPI AG 2019-01-01
• Series: Microorganisms
• Subjects: <i>Coccidioides immitis</i>; Valley Fever; biocontrol; microbial antagonists; challenge assays; arid soils
• Online Access: https://www.mdpi.com/2076-2607/7/2/31

The incidence of coccidioidomycosis, also known as Valley Fever, is increasing in the Southwestern United States and Mexico. Despite considerable efforts, a vaccine to protect humans from this disease is not forthcoming. The aim of this project was to isolate and phylogenetically compare bacterial species that could serve as biocontrol candidates to suppress the growth of <i>Coccidioides immitis</i>, the causative agent of coccidioidomycosis, in eroded soils or in areas close to human settlements that are being developed. Soil erosion in <i>Coccidioides</i> endemic areas is leading to substantial emissions of fugitive dust that can contain arthroconidia of the pathogen and thus it is becoming a health hazard. Natural microbial antagonists to <i>C. immitis</i>, that are adapted to arid desert soils could be used for biocontrol attempts to suppress the growth of the pathogen in situ to reduce the risk for humans and animals of contracting coccidioidomycosis. Bacteria were isolated from soil samples obtained near Bakersfield, California. Subsequently, pairwise challenge assays with bacterial pure cultures were initially performed against <i>Uncinocarpus reesii</i>, a non-pathogenic relative of <i>C. immitis</i> on media plates. Bacterial isolates that exhibited strongly antifungal properties were then re-challenged against <i>C. immitis</i>. Strongly anti-<i>C. immitis</i> bacterial isolates related to <i>Bacillus subtilis</i> and <i>Streptomyces</i> spp. were isolated, and their antifungal spectrum was investigated using a selection of environmental fungi.