Effect of sub-lethal treatment with formalin on the germination of Aspergillus fumigatus spores

Rodent Models of Invasive Aspergillosis due to Aspergillus fumigatus: Still a Long Path toward Standardization

Invasive aspergillosis has been studied in laboratory by the means of plethora of distinct animal models. They were developed to address pathophysiology, therapy, diagnosis, or miscellaneous other concerns associated. However, there are great discrepancies regarding all the experimental variables of animal models, and a thorough focus on them is needed. This systematic review completed a comprehensive bibliographic analysis specifically-based on the technical features of rodent models infected with Aspergillus fumigatus. Out the 800 articles reviewed, it was shown that mice remained the preferred model (85.8% of the referenced reports), above rats (10.8%), and guinea pigs (3.8%). Three quarters of the models involved immunocompromised status, mainly by steroids (44.4%) and/or alkylating drugs (42.9%), but only 27.7% were reported to receive antibiotic prophylaxis to prevent from bacterial infection. Injection of spores (30.0%) and inhalation/deposition into respiratory airways (66.9%) were the most used routes for experimental inoculation. Overall, more than 230 distinct A. fumigatus strains were used in models. Of all the published studies, 18.4% did not mention usage of any diagnostic tool, like histopathology or mycological culture, to control correct implementation of the disease and to measure outcome. In light of these findings, a consensus discussion should be engaged to establish a minimum standardization, although this may not be consistently suitable for addressing all the specific aspects of invasive aspergillosis.

Effect of formalin on the survival of systemic fungi in tissue

Stock cultures of Blastomyces dermatitidis, Candida albicans, Cryptococcus neoformans, Histoplasma capsulatum and Sporothrix schenckii were grown in yeast phase on Sabouraud dextrose agar. Standardized suspensions (10(8) colony forming units/ml) were made and 1. the organisms treated for various times with 10% formalin/acetate buffer; 2. aliquots injected into the tail veins of Swiss-Webster mice. Minimal fungistatic and fungicidal concentrations of formalin were also determined. Five minutes or more of formalin treatment killed all organisms, in vitro, except C. albicans which withstood the 5-minute but not the 30-minute treatment. All fungi, except H. capsulatum which was not recovered, were cultured from mouse heart, kidneys, spleen, lungs and liver prior to but not after 5-minute formalin treatment. All yeasts were susceptible to concentrations of less than 1% formalin. These results emphasize the extreme fungicidal activity of 10% formalin and the uselessness of culturing even very briefly-fixed tissue.