Stimulated Raman Imaging Reveals Aberrant Lipogenesis as a Metabolic Marker for Azole-Resistant Candida albicans

Candida albicans is the single most prevalent cause of fungal bloodstream infections worldwide causing significant mortality as high as 50 percent. This high mortality rate is, in part, due to the inability to initiate an effective antifungal therapy early in the disease process. Mortality rates significantly increase after 12 hours of delay in initiating the appropriate antifungal therapy following a positive blood culture. Early administration of appropriate antifungal therapy is hampered by the slow turnovers of the conventional antimicrobial testing techniques, which require days of incubation. To address this unmet need, we explored the potential of employing stimulated Raman scattering (SRS) imaging to probe for metabolic differences between fluconazole-susceptible and -resistant strains at a single cell level in search of a metabolic signature. Metabolism is integral to pathogenicity. Since only a few hours are needed to observe a full metabolic cycle in C. albicans, metabolic profiling provides an avenue for rapid antimicrobial susceptibility testing. C-H frequency (2850 cm-1) SRS imaging revealed a substantial difference in lipogenesis between the fluconazole-susceptible and -resistant C. albicans. Exposure to fluconazole, an antimicrobial drug that targets ergosterol biosynthesis, only affected the lipogenesis in the susceptible strain. These results show that single cell metabolic imaging via SRS microscopy can be used for rapid detection of antimicrobial susceptibility.