Figure 4

C. albicans HBF have a significant impact on morbidity and mortality rate in vivo . Larvae of G. mellonella were infected with C. albicans LBF or HBF at 1 × 10⁵ CFU/larva and monitored over a period of 7 days (A). Kaplan-Meier plots of G. mellonella survival after injection of C. albicans demonstrated a strain dependant variation in pathogenicity in vivo. Groups of HBF and LBF clinical isolates were compared to each other and to the SC5314 type strain. The HBF isolates resulted in higher killing rate compared to LBF and SC5314. In contrast, LBF isolates exhibit a slower rate of kill and 100% mortality did not occur within 7 days. PBS injected larvae were included as a negative control. (B) I nfected larvae were formalin fixed and sectioned for histology analysis. At 24 h, LBF infected larvae (i) had several melanisation spots and nodules were present mainly under the cuticle and in the peripheral fat body (Feulgen staining, 20× original magnification (o.m.); inset: 4× o.m.), whereas HBF infected larvae (iv) had larger nodules with a greater melanin deposition characterised by the recruitment in the external layers of a huge number of haemocytes (20× o.m.; inset: 10× o.m). At 48 h, LBF (ii) small nodules containing both yeast and some hyphae were observed deeper in the larval tissues, sometimes reaching the external part of the gut wall (PAS staining, 20× o.m.; inset: 10× o.m), with HBF (v) having elongated hyphae targeting the intestinal walls (PAS staining, 40× o.m.; inset: 10× o.m.) At 72 h, LBF (iii) showed segmental invasion of the gut walls (PAS staining, 20× o.m.; inset: 10× o.m.) however, HBF (vi) displayed hyphae endoluminal invasion after breaching the intestinal wall (PAS staining, 40× o.m.; inset: 10× o.m.) with few yeast cells.