Valley Fever on the Rise-Searching for Microbial Antagonists to the Fungal Pathogen Coccidioides immitis.

Antje Lauer,Alex Valenzuela,Gerry Guibert,Joe Baal,Susan Mendes,Alyce Passaglia,Kayla Casimiro

doi:10.3390/microorganisms7020031

Abstract

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 Coccidioides immitis, the causative agent of coccidioidomycosis, in eroded soils or in areas close to human settlements that are being developed. Soil erosion in Coccidioides 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 C. immitis, 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 Uncinocarpus reesii, a non-pathogenic relative of C. immitis on media plates. Bacterial isolates that exhibited strongly antifungal properties were then re-challenged against C. immitis. Strongly anti-C. immitis bacterial isolates related to Bacillus subtilis and Streptomyces spp. were isolated, and their antifungal spectrum was investigated using a selection of environmental fungi.

Highlights

Valley Fever, known as coccidioidomycosis, is an infection caused by the ascomycete fungal pathogens Coccidioides spp
The dimorphic C. immitis and C. posadasii are endemic to soils of American deserts and semi-arid regions where they can live as soil saprophytes
C. immitis is thought to be endemic to the Southern San Joaquin Valley, whereas C. posadasii is predominantly localized in Southern Arizona, but it has been detected in other states of the Southwestern United States, such as Texas, Nevada, New Mexico, and areas in Mexico and South America [1,2]

Summary

Introduction

Valley Fever, known as coccidioidomycosis, is an infection caused by the ascomycete fungal pathogens Coccidioides spp. C. immitis is thought to be endemic to the Southern San Joaquin Valley, whereas C. posadasii is predominantly localized in Southern Arizona, but it has been detected in other states of the Southwestern United States, such as Texas, Nevada, New Mexico, and areas in Mexico and South America [1,2]. Coccidioides spp. are considered to be maintained in rodent reservoirs [6,7], arthroconidia of the pathogen can become airborne when they grow as a soil saprophyte following soil disruption. When inhaled, these dormant forms of the pathogen can infect the lung of humans and animals, primarily mammals [8,9]

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