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Evaluation of media for selective isolation of yeasts from oral, rectal, and burn wound specimens
Abstract:
Six media were evaluated to determine their ability to isolate yeasts and inhibit bacteria. The media included the following: Snyder, Snyder tellurite, Sabouraud tellurite, Littman-gentamicin, molybdate, and Mycosel (BBL). Doses of mixed intestinal gram-negative bacilli and enterococci were most effectively inhibited by Snyder tellurite agar. Klebsiella pneumoniae was the most common bacterial contaminant of the other media. All six media were comparable in isolating yeasts while preventing the growth of the oral bacterial flora. The selection of a basal fungal growth medium for tellurite incorporation to inhibit bacteria but permit growth of yeasts was affected by pH. The bacteriostatic effect of tellurite was decreased with increasing pH of media while fungistatic action was increased. The arbitrary selection of Snyder and Littman agars to isolate yeast from burn wound cultures demonstrated the need to include a selective medium for these specimens. Blood, phenylethyl alcohol blood agar, and Columbia CN blood agar were all inadequate for isolating yeasts from burns. Growth of a variety of filamentous saprophytic and pathogenic dimorphic fungi grew adequately on four of five selective media tested.
Insights
This study evaluated six media for isolating yeasts and inhibiting bacteria. Snyder tellurite agar best inhibited gram-negative bacilli and enterococci, while all media effectively isolated yeasts from oral flora.
Area of Science:
- Medical Mycology
- Microbiology
Background:
- Accurate isolation of yeasts from clinical specimens is crucial for diagnosis.
- Bacterial contamination often hinders yeast recovery from diverse sources, including burn wounds.
- Selective media are essential for differentiating fungal pathogens from commensal flora.
Purpose of the Study:
- To evaluate the efficacy of six different culture media in isolating yeasts.
- To assess the ability of these media to inhibit common bacterial contaminants.
- To determine the impact of pH on the performance of tellurite-containing media.
Main Methods:
- Six media (Snyder, Snyder tellurite, Sabouraud tellurite, Littman-gentamicin, molybdate, Mycosel) were tested.
- Inhibition of mixed intestinal gram-negative bacilli and enterococci was assessed.
- Bacterial contamination, particularly Klebsiella pneumoniae, was monitored.
- Yeast isolation from oral flora and burn wound cultures was compared.
- The effect of pH on tellurite's bacteriostatic and fungistatic properties was investigated.
Main Results:
- Snyder tellurite agar demonstrated superior inhibition of gram-negative bacilli and enterococci.
- Klebsiella pneumoniae was the predominant bacterial contaminant across most tested media.
- All six media showed comparable performance in isolating yeasts while suppressing oral bacterial flora.
- Increasing pH reduced tellurite's bacteriostatic effect but enhanced its fungistatic action.
- Standard blood agars were inadequate for yeast isolation from burn wounds, highlighting the need for selective media.
Conclusions:
- Selective media are vital for accurate yeast isolation, especially from challenging specimens like burn wounds.
- Snyder tellurite agar offers effective bacterial inhibition for yeast recovery.
- The pH of the medium significantly influences the performance of tellurite-based selective agents.
