Abstract 912 Poster Session IV, Tuesday, 5/4 (poster 132)

It is generally accepted that increased intestinal colonization is a predisposing factor for systemic candidiasis, although the mechanisms facilitating host colonization with Candida albicans remain unclear. Because previous studies have indicated that the C. albicans INT1 gene may be linked to filament formation, epithelial adhesion (HeLa cells), and mouse virulence, experiments were designed to clarify the effect of INT1 on cecal colonization in antibiotic-treated mice, with colonization defined as microbial persistence and replication within a tissue. Mice were given drinking water containing 1 mg/ml bacitracin, 2 mg/ml streptomycin, and 0.1 mg/ml gentamicin for 3d prior to oral inoculation of separate groups of mice with 1000 C. albicans CAF2 (INT1/INT), CAG1 (INT1/int1), CAG3 (int1/int1), or CAG5 (int1/int1+INT1). (Each C. albicans strain was constructed using the Ura-blaster technique with the INT1 locus closely linked to URA3.) Antibiotics were continued for the duration of the experiment, and mice were sacrificed 3 and 7 d later for quantitative analysis of cecal C. albicans (n=12-16/strain/d). On day 3, the numbers (avg log 10±SE) of viable cecal CAF2, CAG1, CAG3, and CAG5 were 5.4±0.4, 3.9±0.3, 3.7±0.3, and 4.2±0.4, respectively; on day 7, these numbers were 5.9±0.4, 4.5±0.4, 4.1±0.4, and 4.8±0.4, respectively. Thus, the numbers of CAG3 (int1/int1) were consistently lowest, although not statistically different from those of the strains with one functional INT1 gene, CAG1 and CAG5. The numbers of CAF2 (INT1/INT1) were consistently increased (P≤0.01, ANOVA followed by Fisher's test) compared to each of the other three strains. All recovered C. albicans colonies grew on an agar medium lacking uracil, indicating that the URA3 locus remained stable in vivo. Using specific primers for the INT1 locus, PCR was also used to verify that C. albicans recovered from mouse ceca had the genotype of the inoculated strain. Cross sections of toludine stained ileal tissue were observed by light microscopy; only occasional yeast forms appeared adherent to the intestinal epithelium, but all four C. albicans strains were easily observed in the ileal lumen as budding yeast and filamentous forms. Thus, C. albicans readily colonized and replicated in the ceca of antibiotic-treated mice, and the presence of two functional copies of INT1 was associated with increased cecal colonization that did not appear due to increased epithelial adherence of the colonizing strain.