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Microbiology Testing FAQs — Methods & Media | HiMedia USA
What is LST Broth?
Selective lactose broth containing lauryl sulfate inhibiting gram-positives. Used for presumptive coliform test in water/food. Gas in Durham tube = presumptive coliforms.
What is Slanetz and Bartley Medium used for?
Slanetz and Bartley Medium is selective medium for enumeration of fecal streptococci/enterococci in water by membrane filtration per ISO 7899-2 and EPA Method 1600. Contains sodium azide and crystal violet inhibiting gram-negative bacteria. Enterococci produce maroon/dark red colonies after 44 hours at 35-37°C. Used for: (1) Recreational water monitoring, (2) Drinking water testing, (3) Fecal pollution indicators. Enterococci more stable in seawater than E. coli, better indicator for marine recreational water. Confirm colonies on Bile Esculin Azide Agar.
What is R2A Agar used for?
R2A Agar is low-nutrient medium for cultivation of heterotrophic bacteria from water, particularly chlorine-treated drinking water and oligotrophic (low-nutrient) environments. Lower nutrient levels (compared to PCA/TSA) and longer incubation allow recovery of slow-growing, stressed, or chlorine-injured bacteria that won't grow on rich media. Used for: (1) Drinking water heterotrophic plate count per EPA, (2) Pharmaceutical water testing, (3) Reverse osmosis water monitoring, (4) Cannabis irrigation water testing. Incubate 5-7 days at 25-28°C (not 35-37°C).
What is EC Broth used for?
EC (E. coli) Broth is selective medium for detection and confirmation of E. coli from water samples. Contains bile salts inhibiting gram-positives and lactose for E. coli fermentation. Used in: (1) Fecal coliform confirmation (water MPN method), (2) E. coli detection at 44.5-45.5°C (elevated temperature), (3) Drinking water quality, (4) Cannabis BTGN testing confirmation. Procedure: Transfer presumptive positive tubes from Lactose Broth to EC Broth, incubate 24h at 44.5°C in water bath. Gas production confirms fecal coliforms/E. coli. Part of standard MPN confirmation. The composition and performance criteria of this medium are as per the specifications laid down in ISO/DIS 7251:2005.
What is MUG?
MUG (4-methylumbelliferyl-β-D-glucuronide) detects E. coli beta-glucuronidase. Fluorescence under UV = E. coli. Rapid E. coli confirmation in water testing (24h). Recommended for identification of Escherichia coli and coliform bacteria from water samples by a fluorogenic assay
method.
What is Peptone Water used for?
Peptone Water is simple basal medium used for: (1) Dilution blank for microbiological testing, (2) Rinsing containers, (3) Indole test, (4) General cultivation of non-fastidious organisms, (5) Base for adding supplements. Contains only peptone (15 g/L) and sodium chloride (5 g/L). Provides basic nutrients without selective agents. For indole test: inoculate, incubate 24h, add Kovac's reagent - red ring = indole positive (E. coli). Widely used as multipurpose medium and diluent in food and water microbiology.
What is Lactose Broth used for?
Lactose Broth is used for presumptive coliform testing in food and water by Multiple Tube (MPN) method. Contains: lactose (fermentable sugar), peptone (nutrients), Durham tube (inverted tube to trap gas). Procedure: (1) Inoculate dilutions into lactose broth tubes, (2) Incubate 24-48 hours at 35°C, (3) Gas production (visible in Durham tube) = presumptive positive for coliforms, (4) Confirm positives with Brilliant Green Bile Broth or EMB/MacConkey. MPN tables used to estimate coliform count from pattern of positive tubes. Classic water testing method, largely replaced by membrane filtration.
What is Brilliant Green Bile Broth used for?
Brilliant Green Bile Broth (BGBB) is selective medium for confirmation of coliforms from presumptive Lactose Broth MPN tests. Contains: (1) Brilliant green and bile salts - inhibit gram-positives and non-coliforms, (2) Lactose - fermented by coliforms, (3) Durham tube - detects gas. Procedure: Transfer gas-positive Lactose Broth tubes to BGBB, incubate 48 hours at 35°C. Gas in Durham tube = confirmed coliforms. Used in water quality testing, food microbiology. Part of standard MPN confirmation process. Also called 2% Brilliant Green Lactose Bile Broth.
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.