Clearing the FoG: Antifungal tolerance is a subpopulation effect that is distinct from resistance and is associated with persistent candidemia

Alexander Rosenberg; Iuliana V. Ene; Maayan Bibi; Shiri Zakin; Ella Shtifman Segal; Naomi Ziv; Alon M. Dahan; Arnaldo L. Colombo; Richard J. Bennett; Judith Berman

A number of C. albicans growth parameters did not correlate with FoG levels. These 190 included cell viability in the presence of drug (Fig. 2h) , consistent with FLC being fungistatic 191 rather than fungicidal. Unlike tolerant bacteria, which display reduced growth rates and longer 192 colony appearance times 2,75-77 , antifungal tolerance did not correlate with slower growth in three Decreased intracellular drug levels underlie increased tolerance. A recently developed 206 fluorescent azole probe, FLC-Cy5 81 , provides a powerful tool to monitor intracellular drug levels 207 and uptake rates using flow cytometry (Fig. 3a) . The initial rate of FLC-Cy5 uptake per cell 208 varied between strains and showed a weak inverse correlation with FoG levels (R 2 = 0.64, P = 209 0.12, Fig. 3b ). By contrast, steady state FLC-Cy5 levels at 24 h correlated inversely with FoG 210 levels (R 2 = 0.8, P < 0.01, Fig. 3c ). Cells were categorized as having low, mid, and high levels of