Masters Thesis

Murine Modeling of Ascending Urinary Tract Candidiasis to Identify Better Treatment Options

BACKGROUND: 10-15% of nosocomial urinary tract infections are caused by Candida spp. in individuals with indwelling catheters, especially those in the ICU or residents in assisted living settings. These infections are increasingly being caused by organisms resistant to the traditional oral azole or intravenous echinocandin treatments making it necessary to identify alternative therapies. Given the reduced toxicity of liposomal amphotericin B (AmBisome®, AmBi) compared to amphotericin B deoxycholate (Fungi), and AmBi’s effectiveness against strains resistant to echinocandin or azole drugs, we explored the possibility that AmBi could be used as an alternative treatment option for UTC. METHODS: To establish UTC in Swiss Webster female mice, cyclophosphamide or triamcinolone immunosuppressed mice were sedated with a ketamine/xylazine solution, and infected with differing amounts of yeast cells to find a dose that would produce the desired infection levels. Models were established for 4 different Candida strains: azole sensitive (AS) C. albicans (CP#620), azole resistant (AR) C. albicans (ATCC#62342), echinocandin sensitive (ES) C. glabrata (CP#609), and echinocandin resistant (ER) C. glabrata (ATCC#17351)., C. albicans CP#620 challenged groups of mice were euthanized starting one day after challenge for 5 days to track the spread of the infection over 5 days. Treatment studies using C. albicans CP#620 were done to compare efficacy and toxicity of AmBi to Fungi, looking specifically at varying dosing amounts, duration of treatment, and delivery by intravenous (IV) or as a bladder lavage (LAV). Treatment of AS or AR C. albicans (CP#620 or ATCC#62342, respectively) infected animals was done to compare the efficacy of AmBi IV or LAV or Fluconazole per os (PO). Additionally, treatment studies of ES or ER C. glabrata infected animals (CP#609 or ATCC#17351, respectively) was done to compare the efficacy of AmBi IV or LAV or caspofungin IV or LAV. For these studies, bladder, kidneys, liver, and spleen were collected for CFU/g, histopathology and drug concentration determination. RESULTS: We found doses of yeast that produced an ascending UTC in Swiss Webster female mice for all strains of Candida tested. AS C. albicans quickly spread systemically but by d+5 infection was only detectable in the bladder and kidneys. AS C. albicans infection in the bladder was consistently reduced to undetectable levels by AmBi IV or LAV or Fungi IV or LAV drug treated mice, while non-drug treated control groups had pronounced infection. The 7.5 mg/kg AmBi administered 5TX was significantly better than treating 3TX but not significantly better than treating 7X. AmBi and Fungi have similar efficacy both IV or LAV, but Fungi LAV treatment resulted in lethal amphotericin B related toxicity. This toxicity was not observed in AmBi treated mice. AS and AR strains of C. albicans were effectively treated by AmBi IV or LAV or Fluconazole PO. ES C. glabrata was effectively treated by AmBi IV or LAV or caspofungin IV or LAV, reducing the infection in both the bladder and the kidneys compared to control. iv ER C. glabrata treated by AmBi IV or LAV reduced the infection in the bladder and kidneys compared to control; Caspofungin treatment significantly reduced infection in the kidney but not the bladder of IV treated mice and reduced infection in the bladder but not the kidney in LAV treated mice. AmBi and Fungi have the same positive efficacy against UTI caused by an AR C. albicans, but they differ in their kidney and bladder toxicity depending upon the drug dose. CONCLUSIONS: We have demonstrated that an ascending UTC can be established in mice which localizes in the bladder and kidneys, and this model can be used to compare antifungal drug efficacy for UTC. The same lavage dose of AmBi or Fungi (200 μg) cleared the infection in the bladder but Fungi was associated with severe bladder toxicity and even death of some of the animals while AmBi LAV at the same dose was non-toxic. AmBi IV or LAV can also effectively treat infections caused by Candida spp that are resistant to the more commonly used azole or echinocandin drugs. Therefore, AmBi LAV treatment of the UTC was effective and safe and this approach needs to be investigated further.

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