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Microbiology Testing FAQs — Methods & Media | HiMedia USA
What is TGE Agar used for?
Tryptone Glucose Extract (TGE) Agar is general-purpose medium for plate counts of bacteria in milk and dairy products per Standard Methods for Dairy Products. Similar to PCA but optimized for dairy. Contains tryptone, glucose, beef extract. Used for: (1) Standard plate count in milk, (2) Dairy product testing, (3) Cultured dairy products, (4) Ice cream testing. Supports good recovery of psychrotrophic bacteria from refrigerated dairy. Incubate 32°C for 48 hours (dairy standard). Provides accurate counts with minimal interference from dairy matrix.
What is VRBA used for?
Violet Red Bile Agar (VRBA) is selective medium for enumeration of coliform bacteria in dairy products, food, and water per ISO 4832, APHA methods. Contains: (1) Crystal violet and bile salts - inhibit gram-positives, (2) Lactose - differentiate coliforms, (3) Neutral red - pH indicator. Coliforms produce purple-red colonies with purple halos (acid from lactose fermentation precipitates bile). Used for: (1) Coliform count in milk/dairy, (2) Food quality testing, (3) Process hygiene monitoring. Pour plate or surface spread method. Incubate 24 hours at 35-37°C.
How do I perform membrane filtration coliform test with M-Endo?
Membrane filtration procedure: (1) Filter appropriate Water volume through 0.45μm membrane (100mL for drinking Water, diluted samples for contaminated Water), (2) Aseptically transfer membrane to M-Endo Agar pad in petri dish, (3) Incubate 22-24 hours at 35°C, (4) Count colonies with pink-red color and golden metallic sheen, (5) Calculate coliforms per 100mL: (colonies counted × 100) / mL filtered. Colonies without sheen are non-coliforms. Confirm suspect colonies with biochemical tests if required by method.
What is M-Endo Agar LES used for?
M-Endo Agar LES (Membrane-Endo Agar Les Endo Substrate) is used for detection and enumeration of coliform bacteria in Water by membrane filtration method per EPA and Standard Methods. After filtering Water through 0.45μm membrane, place filter on M-Endo Agar and incubate 22-24 hours at 35°C. Coliform colonies appear pink/red/dark red with golden metallic sheen (lactose fermentation). This sheen is diagnostic for coliforms. LES formulation has improved selectivity over original Endo formulations. Used for drinking Water, recreational Water, wasteWater testing.
What is GVPC and why is it added to BCYE?
GVPC is antibiotic supplement added to BCYE for selective isolation of Legionella from contaminated environmental samples (Water systems, biofilms). GVPC contains: Glycine - inhibits gram-positive bacteria, Vancomycin - inhibits gram-positive bacteria, Polymyxin B - inhibits gram-negative bacteria except Legionella, Cycloheximide (anisomycin) - inhibits fungi. This combination suppresses background microflora that would overgrow Legionella. Use BCYE with GVPC for environmental samples. Use BCYE without GVPC for clinical specimens (less contamination, antibiotics may inhibit some Legionella strains).
Why does Legionella require specialized media?
Legionella bacteria are fastidious and will not grow on standard media (TSA, Blood Agar). They have unique requirements: (1) L-cysteine (amino acid) - absolutely essential, cannot synthesize it, (2) Iron (ferric iron) - required for metabolism, (3) Charcoal - absorbs inhibitory compounds produced during growth, (4) Neutral-to-alkaline pH (6.9-7.0) - maintained by ACES buffer. Standard media lack cysteine and adequate buffering. BCYE specifically formulated to meet these requirements. Legionella will not grow without cysteine supplementation.
What is BCYE Agar used for?
Buffered Charcoal Yeast Extract (BCYE) Agar is the primary medium for isolation and cultivation of Legionella species from environmental and clinical samples. Legionella pneumophila causes Legionnaires' disease. BCYE contains: (1) L-cysteine and ferric pyrophosphate (required growth factors), (2) Activated charcoal (absorbs toxic metabolites), (3) ACES buffer (maintains pH), (4) Yeast extract (nutrients). Use BCYE with antibiotics (GVPC supplement) for selective isolation from environmental Water samples. Incubate 3-10 days at 35-37°C with 2.5% CO2.
What is M17 Medium used for?
M17 Medium is selective for thermophilic Lactococcus and Streptococcus species used in dairy fermentation. Developed for Streptococcus thermophilus in yogurt. Contains: (1) Disodium glycerophosphate - buffer, (2) Ascorbic acid - reducing agent, (3) Magnesium sulfate - stimulates lactic acid bacteria. Used for: (1) Yogurt starter culture enumeration, (2) Cheese culture testing, (3) S. thermophilus counts in dairy, (4) Probiotic product QC. Incubate anaerobically at 42-43°C for 48 hours (S. thermophilus optimal). Add agar for solid medium. For cultivation of lactic Streptococci and plaque assay of lactic bacteriophages.
How Milk agar different from skim milk agar?
Similar to skim milk agar but may contain additional nutrients. Used for dairy microbiology, casein breakdown testing.
How to perform test for proteolysis?
Skim milk agar tests protease enzymes. Clear zones around colonies = casein hydrolysis (protease). Used for dairy microbiology, Bacillus identification. Recommended for cultivation and enumeration of microorganisms encountered in dairy industry.