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Microbiology Testing FAQs — Methods & Media | HiMedia USA
How much does 500g of PDA make?
500g of Potato Dextrose Agar powder makes approximately 12.8 liters of prepared medium (39g per liter). Volume calculations: In 90mm plates (20mL/plate): 500g yields ~640 plates. In bottles (200mL): 500g yields ~64 bottles. Cost analysis for cannabis testing facility testing 100 samples/day with 3 plates per sample (300 plates/day): 500g supplies 2 days. Monthly need (6,000 plates) = 4.7kg PDA powder. RTU plates may be more cost-effective for this volume due to labor savings.
Should I add antibacterial to PDA?
YES, adding chloramphenicol (50-100 mg/L) or other broad-spectrum antibiotic to PDA is highly recommended when testing samples with bacterial contamination (cannabis, food, soil, environmental). Add antibiotic AFTER autoclaving when medium cools to 45-50°C (heat destroys antibiotics). Without antibacterial agents, bacterial overgrowth can obscure fungal colonies. For pure fungal cultures or samples with minimal bacteria, antibacterial may be omitted. For isolation and enumeration of yeasts and moulds from dairy and other food products.
What is Czapek Dox Agar used for?
Czapek Dox Agar (also Czapek's Agar) is defined synthetic medium for cultivation and identification of Aspergillus and Penicillium species. Contains sucrose as sole carbon source, sodium nitrate as nitrogen source, minimal nutrients. Used for: (1) Fungal taxonomy and identification, (2) Aspergillus species differentiation, (3) Mycology research, (4) Testing fungal nutritional requirements. Growth characteristics on Czapek Dox help identify specific species. Some fungi grow well (Aspergillus niger), others poorly or not at all (aids differentiation). Incubate 5-7 days at 25-28°C.
When should I use SDA vs PDA for fungal cultivation?
Both support fungi, but different applications: SDA (pH 5.6, high dextrose) - preferred for pathogenic fungi in clinical mycology, better for yeast isolation, pharmaceutical USP testing, defined formulation for consistency. PDA (pH 5.6, potato infusion) - preferred for plant pathogenic fungi, food mycology, general environmental molds, complex nutrients support sporulation. For clinical specimens → SDA. For cannabis/food TYMC → PDA. For pharmaceutical microbial limits → either acceptable but SDA more standardized. Both should be supplemented with antibacterial agents when testing heavily contaminated samples.
What is Sabouraud Dextrose Agar used for?
Sabouraud Dextrose Agar (SDA) is the standard medium for cultivation of yeasts and molds, particularly pathogenic fungi. Low pH (5.6) and high dextrose content favor fungal growth while inhibiting most bacteria. Used for: (1) Clinical mycology - fungal infections, (2) Pharmaceutical microbial limits (USP <61>/<62>), (3) Environmental monitoring for fungi, (4) Food mycology, (5) Antifungal susceptibility testing. Add chloramphenicol (antibacterial) when bacterial contamination expected. Incubate 25-28°C for 5-7 days (extend to 30 days for slow-growing dimorphic fungi).