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Effect of formalin on the survival of systemic fungi in tissue
Abstract:
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.
Insights
Ten percent formalin rapidly kills pathogenic fungi like Blastomyces dermatitidis and Histoplasma capsulatum, making tissue cultures unreliable after even brief fixation.
Area of Science:
- Mycology
- Infectious Diseases
- Medical Microbiology
Background:
- Fungal infections pose significant health risks.
- Effective sterilization and inactivation methods are crucial for laboratory and clinical settings.
- Formalin is a common fixative and disinfectant.
Purpose of the Study:
- To evaluate the fungicidal efficacy of 10% formalin against common pathogenic fungi.
- To determine the minimum fungistatic and fungicidal concentrations of formalin.
- To assess the impact of formalin fixation on the recoverability of fungi from infected tissues in vivo.
Main Methods:
- Stock cultures of five pathogenic fungi (Blastomyces dermatitidis, Candida albicans, Cryptococcus neoformans, Histoplasma capsulatum, Sporothrix schenckii) were prepared.
- Organisms were treated with 10% formalin for varying durations.
- In vitro fungicidal and fungistatic concentrations were determined.
- Mice were infected, and formalin-treated fungal aliquots were injected to assess in vivo inactivation and subsequent tissue culturing.
Main Results:
- In vitro, 5 minutes of 10% formalin treatment killed all tested fungi except Candida albicans, which required 30 minutes.
- In vivo, fungi were not recovered from mouse tissues after a 5-minute formalin treatment.
- All tested yeasts demonstrated susceptibility to less than 1% formalin concentrations.
Conclusions:
- 10% formalin exhibits potent and rapid fungicidal activity against a range of pathogenic fungi.
- Even brief formalin fixation (5 minutes) effectively inactivates fungi, rendering subsequent tissue cultures unreliable for diagnosis.
- Formalin is a highly effective agent for fungal inactivation in laboratory and clinical contexts.