Increase of virulence and its phenotypic traits in drug-resistant strains

1 There is concern about the rise of antifungal drug resistance but little is known about 2 comparative biological properties and pathogenicity of drug-resistant strains. We 3 generated fluconazole (FLC; CO23RFLC) or micafungin (FK; CO23RFK)-resistant 4 strains of Candida albicans by treating a FLCand FK-susceptible strain of this 5 fungus (CO23S) with stepwise increasing concentrations of either drug. Molecular 6 analyses showed that CO23RFLC had acquired markedly increased expression of the 7 drug-resistance MDR1 efflux pump MDR1 gene, whereas CO23RFK had a homozygous 8 mutation in the FSK1 gene. These genetic modifications did not alter to any extent the 9 growth capacity of the drug-resistant strains , either at 28°C or at 37°C in vitro, but 10 markedly increased their experimental pathogenicity in a systemic mouse infection 11 model, as assessed by the overall mortality and target organ invasion. Interestingly, 12 no apparent increase in the vaginopathic potential of the strains was observed in a 13 oestrogen-dependent rat vaginal infection. The increased pathogenicity of drug14 resistant strains for systemic infection was associated with a number of biochemical 15 and physiological changes, inclusive of i) marked cellular alterations associated with 16 a different expression and content of major cell wall polysaccharides; ii) more rapid 17 and extensive hyphae formation both in liquid and solid media; iii) increased 18 adherence to plastic and propensity for biofilm formation. Overall, our data 19 demonstrate that experimentally-induced resistance to antifungal drugs, irrespective 20 of drug family, can substantially divert C. albicans biology, particularly affecting 21 biological properties of potential relevance for deep-seated candidiasis. 22