## 3 Results
### Susceptibility to Antifungal Agents  
As an opportunistic pathogen, the susceptibility of C. albicans to antifungal agents is an important consideration with regard to spaceflight crew safety. This becomes even more critical based on our previous findings that yeast cultured in analog bioreactors (HARV) have an increased resistance to AmB [31]. As such, the ability of C. albicans to grow in the presence of two antifungal agents (AmB and CAS) was evaluated both by treating cells during the mission while in microgravity, as well as on yeast returned live following the conclusion of the flight. The Micro-6 payload was specifically designed to evaluate yeast growth in the presence of AmB while in microgravity. Cell growth was activated by the addition of medium containing 0.12 mg/L and 0.25 mg/L AmB and the samples were fixed following the growth period. Upon conclusion of the mission cell counts were performed to indicate the susceptibility of C. albicans to the cytotoxic effects of the antifungal agent (Figure 8A). AmB susceptibility was also evaluated in cells returned viable and exposed to drug following the mission, using CFU as the viability indicator. Interestingly, the AmB susceptibility results from the Micro-6 payload were nearly identical, regardless of whether drug exposure was in microgravity (Figure 8A) or following post-flight cultivation (Figure 8B). Although both doses of AmB impacted yeast growth, flight cells were more resilient than terrestrial control cells in the presence of the highest dose of AmB (0.25 mg/L). The Micro-14/FEP payload was also designed to evaluate antifungal sensitivity in microgravity. Parent cultures were serially passaged as described in Methods. On two separate occasions during the serial growth (following day 1 and 3 for AmB or day 2 and 4 for CAS), a dilution of the Large FEP bag culture was used to inoculate Small FEP bags containing antifungal agents (see Figure 1 for experimental design details). On each of the four days of the analysis, yeast were also cultured in control medium and 0.25 mg/L AmB for a direct day-to-day comparison. There was not a notable day-to-day adaptation of yeast to the antifungal agents (data not shown); therefore, samples conducted on the two separate days were treated as replicates and grouped in the analyses described herein. Throughout these studies, there was a consistent trend for the cells cultured without drug to grow to a higher density in flight as compared to terrestrial controls, as demonstrated in Figure 3. In addition, and as illustrated in Figure 8C/D, cells grew to a higher density in all conditions of the FEP payload when compared to Micro-6 FPA samples. Cultures propagated in microgravity were consistently more resistant to AmB than comparable terrestrial controls (\(p<0.006\)). As illustrated in Figure 8C, flight samples grew in the presence of AmB when compared to untreated flight samples (\(p<0.05\)), whereas the growth of terrestrial samples was stagnated in the presence of the antifungal agent when compared to the untreated ground controls (\(p>0.33\)). As such, cells cultured in microgravity were more resistant to all doses of AmB than were the corresponding terrestrial control cells (\(p<0.002\)). In contrast, companion cultures in the Micro-14/FEP payload that were exposed to a functionally distinct antifungal agent, CAS, were susceptible to increasing concentrations of drug, (Figure 8D). When CAS-treated samples were compared to the corresponding control cultures (flight CAS vs. flight YPD; terrestrial CAS vs. terrestrial YPD), the lowest dose had very little impact on cell growth and the highest dose prevented nearly all growth. Only at the intermediate dose of CAS (0.025 mg/L) was there an apparent difference between the impact of the drug on cells cultivated in flight or terrestrially. When compared to the untreated samples, terrestrial controls were more resistant to CAS than the cells cultured in microgravity, although not to the level of significance.