Brammer, B. | bioRxiv Science

bioRxiv2020

Phosphate Induces a Morphological Shift that Enhances Vascular Dissemination of Cryptococcus neoformans

Environmental pathogens, which move from ecological niches to mammalian hosts, must adapt to dramatically different environments. Microbes that disseminate farther, including the fungal meningitis pathogen Cryptococcus neoformans, require additional adaptation to diverse tissues. When C. neoformans enters the lungs, infecting cells (<10 m diameter) enlarge (>30 m diameter), then form a heterogeneous population. The brain contains uniformly small cells ([~]7 m). We demonstrate that formation of a small C. neoformans morphotype - called "seed" cells due to their disseminating ability - is critical for extrapulmonary organ entry. Seed cell formation is triggered by environmental factors, including C. neoformans environmental niche, pigeon guano. The underlying trigger, phosphate, can be released by tissue damage, potentially establishing a feed-forward loop of seed cell formation and dissemination. We demonstrate that C. neoformans size variation is not just a continuum but inducible subpopulations that change host interactions to facilitate microbe survival and spread.

microbiology↗

bioRxiv2019

synergistic and antagonistic drug interactions in the treatment of systemic fungal infections

Invasive fungal infections cause 1.6 million deaths annually, primarily in immunocompromised individuals. Mortality rates are as high as 90% due to limited number of efficacious drugs and poor drug availability. The azole class antifungal, fluconazole, is widely available and has multi-species activity but only inhibits fungal cell growth instead of killing fungal cells, necessitating long treatments. To improve fluconazole treatments, we used our novel high-throughput method, the overlap2 method (O2M), to identify drugs that interact with fluconazole, either increasing or decreasing efficacy. Although serendipitous identification of these interactions is rare, O2M allows us to screen molecules five times faster than testing combinations individually and greatly enriches for interactors. We identified 40 molecules that act synergistically (amplify activity) and 19 molecules that act antagonistically (decrease efficacy) when combined with fluconazole. We found that critical frontline beta-lactam antibiotics antagonize fluconazole activity. A promising fluconazole-synergizing anticholinergic drug, dicyclomine, increases fungal cell permeability and inhibits nutrient intake when combined with fluconazole. In vivo, this combination doubled the time-to-endpoint of mice with disseminated Cryptococcus neoformans infections. Thus, our ability to rapidly identify synergistic and antagonistic drug interactions can potentially alter the patient outcomes.

microbiology↗