Frequently Asked Questions

Chromogenic broth for rapid coliform detection in water. Color change in 24h vs 48h for traditional methods. Purple = E. coli, Pink = other coliforms. For detection of Escherichia coli and coliforms in water samples. The composition and performance criteria of this medium are as per the specifications laid down in ISO 9308-1:2014.

Chromogenic medium for presumptive S. aureus identification. Green-blue colonies in 24h. Faster than traditional Baird Parker requiring 48h. Used for food, clinical screening. For selective medium for the isolation and enumeration of Staphylococcus aureus.

Bile Esculin Agar tests esculin hydrolysis in presence of bile - characteristic of Group D Streptococcus and Enterococcus. Contains: (1) Bile (4%) - inhibits most bacteria, (2) Esculin - hydrolyzed by Group D Strep/Enterococcus, (3) Ferric citrate - reacts with esculetin (esculin breakdown product) producing black color. Positive: growth + black (or brown halo). Used for: (1) Enterococcus identification, (2) Probiotic culture verification (E. faecium common probiotic), (3) Group D Strep testing. Inoculate slant or stab, incubate 48h at 35°C. For differential isolation and presumptive identification of group D Streptococci in food and other products.

Nutrient Broth is simple liquid medium for cultivation of non-fastidious bacteria. Contains beef extract and peptone in water. Used for: (1) General bacterial cultivation, (2) Biomass production for testing, (3) Inoculum preparation, (4) Enrichment (non-selective), (5) Maintaining stock cultures, (6) Teaching laboratories. Less nutrient-rich than TSB or BHI. Sufficient for robust organisms (E. coli, Bacillus, Pseudomonas) but may not support fastidious organisms. Incubate at organism's optimal temperature with shaking if desired for aeration.

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.

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).

Enriched broth for streptococci, especially Group B Strep screening. Used in prenatal GBS screening (vaginal-rectal swabs). Incubate with antibiotics for selective GBS enrichment. For cultivation of group A haemolytic Streptococci used for serological studies.

Enriched broth for fastidious organisms, particularly streptococci and pneumococci. Simpler than BHI. Used for blood culture systems, bacterial cultivation, preparing inocula. For cultivation of a wide variety of fastidious organisms.

Bordet-Gengou Agar is selective medium for Bordetella pertussis isolation from nasopharyngeal swabs. Contains potato infusion, glycerol, and sheep blood. B. pertussis produces small, smooth, pearl-like colonies ("mercury drops"). Incubate 3-7 days in humidified incubator. Largely replaced by Regan-Lowe charcoal agar or PCR, but still used in some labs. For detection and isolation of Bordetella pertussis and Bordetella parapertussis.

Charcoal Agar contains activated charcoal absorbing toxic metabolites and free radicals, improving recovery of fastidious organisms. Used for Bordetella pertussis (whooping cough), Francisella, other fastidious pathogens. Charcoal provides dark background making colony visualization easier. Similar concept to BCYE for Legionella. For cultivation of Bordetella pertussis, for vaccine production and also for stock culture maintenance.

Columbia Blood Agar Base is enriched base medium for blood agar preparation. More nutrient-rich than standard Blood Agar Base. Contains peptones, cornstarch, and sodium chloride. When supplemented with 5-7% sheep blood, supports fastidious organisms: Streptococcus (including S. pneumoniae), Haemophilus (with X+V factors supplement), Corynebacterium, Neisseria. Shows clearer hemolysis patterns than other blood agar bases. Preferred for: (1) Clinical specimens, (2) Throat cultures, (3) Wound cultures, (4) Antimicrobial susceptibility testing. Cornstarch neutralizes toxic metabolites improving organism recovery. The composition and performance criteria of this medium are as per the specifications laid down in ISO 10272-2:2017.

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.

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.

DTM is selective medium for isolation of dermatophytes (Trichophyton, Microsporum, Epidermophyton) from skin, hair, nail specimens. Contains: (1) Cycloheximide and gentamicin - inhibit saprophytic fungi and bacteria, (2) Phenol red pH indicator. Dermatophytes produce alkaline metabolites → medium turns red (yellow to red color change). Saprophytes may grow but don't produce color change or change late. Procedure: Inoculate specimen, incubate at 25-30°C, observe daily. Red color in 3-7 days = presumptive dermatophyte. Confirm with microscopy and subculture. Used in physician offices, clinics for rapid screening.

Middlebrook 7H10 Agar is transparent agar-based medium for mycobacteria (vs egg-based LJ medium). Advantages: (1) Transparent - easier colony observation and counting, (2) Faster growth (2-3 weeks), (3) Better for drug susceptibility testing, (4) Can observe early growth. Requires OADC enrichment (Oleic acid, Albumin, Dextrose, Catalase) added after autoclaving. M. tuberculosis produces characteristic rough, dry, buff colonies. Used in clinical mycobacteriology labs for TB culture and sensitivity.