Anidulafungin in treatment of experimental invasive infection by Candida parapsilosis: in vitro activity, (1-->3)-beta-D-glucan and mannan serum levels, histopathological findings, and in vivo efficacy

Methodologies for in vitro and in vivo evaluation of efficacy of antifungal and antibiofilm agents and surface coatings against fungal biofilms

Unlike superficial fungal infections of the skin and nails, which are the most common fungal diseases in humans, invasive fungal infections carry high morbidity and mortality, particularly those associated with biofilm formation on indwelling medical devices. Therapeutic management of these complex diseases is often complicated by the rise in resistance to the commonly used antifungal agents. Therefore, the availability of accurate susceptibility testing methods for determining antifungal resistance, as well as discovery of novel antifungal and antibiofilm agents, are key priorities in medical mycology research. To direct advancements in this field, here we present an overview of the methods currently available for determining (i) the susceptibility or resistance of fungal isolates or biofilms to antifungal or antibiofilm compounds and compound combinations; (ii) the in vivo efficacy of antifungal and antibiofilm compounds and compound combinations; and (iii) the in vitro and in vivo performance of anti-infective coatings and materials to prevent fungal biofilm-based infections.

Therapies against murine Candida guilliermondii infection, relationship between in vitro antifungal pharmacodynamics and outcome

BACKGROUND

Candida guilliermondii has been recognized as an emerging pathogen showing a decreased susceptibility to fluconazole and considerably high echinocandin MICs.

AIMS

Evaluate the in vitro activity of anidulafungin in comparison to amphotericin B and fluconazole against different isolates of C. guilliermondii, and their efficacy in an immunosuppressed murine model of disseminated infection.

METHODS

The in vitro susceptibility of four strains against amphotericin B, fluconazole and anidulafungin was performed by using a reference broth microdilution method and time-kill curves. The in vivo efficacy was evaluated by determination of fungal load reduction in kidneys of infected animals receiving deoxycholate AMB at 0,8 mg/kg i.v., liposomal amphotericin B at 10 mg/kg i.v., fluconazole at 50 mg/kg, or anidulafungin at 10 mg/kg.

RESULTS

Amphotericin B and anidulafungin showed fungicidal activity, while fluconazole was fungistatic for all the strains. In the murine model, liposomal amphotericin B at 10 mg/kg/day was effective in reducing the tissue burden in kidneys of mice infected with any of the tested strains. However, amphotericin B, anidulafungin and fluconazole were only effective against those strains showing low MIC values.

CONCLUSIONS

Liposomal amphotericin B showed the higher activity and efficacy against the two strains of C. guilliermondii, in contrast to the poor effect of fluconazole and anidulafungin. Further studies with more isolates of C. guilliermondii representing a wider range of MICs should be carried out to assess whether there is any relationship between MIC values and anidulafungin efficacy.

Anidulafungin versus caspofungin in a mouse model of candidiasis caused by anidulafungin-susceptible Candida parapsilosis isolates with different degrees of caspofungin susceptibility

Candida parapsilosis isolates occasionally display resistance in vitro to echinocandins and cause breakthrough infections to echinocandins. The degree of the in vivo cross-resistance among echinocandins and the fitness loss associated with caspofungin (CAS) resistance of C. parapsilosis are not well studied. We compared the activities of CAS and anidulafungin (ANF), each given at 2 dosing schedules (high dose or low dose) in a nonneutropenic mouse model of invasive candidiasis (IC) caused by ANF-susceptible isolates of C. parapsilosis with different degrees of susceptibility to CAS (CAS resistant [CAS-R], MIC, >16 mg/liter; CAS intermediate [CAS-I], MIC, 4 mg/liter; and CAS susceptible [CAS-S], MIC, 2 mg/liter). We analyzed tissue fungal burden, histopathology, and weight loss patterns. Increasing CAS resistance was associated with reduced virulence of C. parapsilosis isolates (mortality rates for CAS-S versus CAS-I versus CAS-R, 100% versus 11.1% versus 0%, respectively; P < 0.001). High doses of either echinocandin were active against infection with the CAS-I isolate when assessed by fungal burden reduction and weight gain. In contrast to CAS-S and CAS-I isolates, there was no reduction in fungal burden in mice infected with the CAS-R isolate following treatment with either echinocandin, each given at a high or low dose. Nevertheless, mice infected with the CAS-R isolate had reduced disease severity following echinocandin treatment, suggesting that echinocandins have activity in vivo, even against echinocandin-resistant strains. A complex interplay of residual echinocandin activity, decreased virulence, and/or fitness of isolates with altered cell wall and possible immunomodulatory effects can be encountered in vivo during infection with CAS-resistant C. parapsilosis isolates.