Lung microbiome influences Coccidioides colonization and invasiveness

Abstract It has long been thought that the lung is a sterile environment; however, recent studies revealed that healthy lungs are colonized by bacteria, fungi, and viruses. Coccidioidomycosis, also known as Valley fever, is a lung infection caused by the fungal species Coccidioides. Because of poor testing strategies 60–80% of patients are treated with antibiotics prior to accurate diagnosis of coccidioidomycosis. This potentially depletes bacteria with symbiotic relationships within the lung microenvironment and promotes susceptibility to invasion by Coccidioides. Coccidioides immitis is a dimorphic fungal pathogens whose fungal life cycle alternates between the saprophytic phase (soil mycelia) and parasitic phase (tissue infecting spherules). Natural microbial antagonists that inhibit soil Coccidioides immitis have been identified; Bacillus subtilis displays antifungal activity against Coccidioides growth through a clear zone of inhibition between fungi and bacteria. Whether these findings hold true in the host phase of the Coccidioides life cycle is unknown but have major implications for patient treatment. Our preliminary data suggest that host microbiome inhibits Coccidioides growth, and antibiotic treatment shifts or depletes the lung microbiome allowing a niche for Coccidioides growth. We are also exploring how this interface between the lung, Coccidioides, and the microbiome influences host innate and adaptive immune responses. Furthermore, these findings could shape the way physicians assess prescription of antibiotics prior to fungal diagnosis.