AuSaMicS Life Science • Water & Food Microbiology

AS-1266 🧫 Presumptive Coliform Medium ✓ Water & Food Testing 🧪 MPN Ready

Use: Coliform presumptive detection Preparation: ~35.6–36.5 g/L Readout: Acid/gas in Durham tube

Lauryl Sulphate Broth (LSB), also widely known as Lauryl Tryptose Broth, is a selective liquid medium used for the presumptive detection of coliform bacteria in water, effluent, sewage, dairy products, and other food samples. It is routinely used in multiple-tube fermentation and Most Probable Number (MPN) workflows where gas formation from lactose serves as a primary indicator of presumptive coliform presence.

The medium was developed to provide rich growth and substantial gas production from even small inocula of coliform organisms while inhibiting much of the accompanying non-coliform flora through sodium lauryl sulphate. This balance makes it valuable as a frontline screening medium before confirmatory testing. citeturn521074search0turn521074search1

LSB remains a routine laboratory medium in water and food microbiology because it combines practical selectivity, straightforward interpretation, and compatibility with standardized coliform testing workflows. It is commonly associated with APHA-type procedures and ISO coliform detection contexts. citeturn521074search0turn521074search1

LSB contains tryptose as a source of nitrogen, amino acids, vitamins, and growth-supporting nutrients; lactose as the fermentable carbohydrate; phosphate salts for buffering; sodium chloride for osmotic balance; and sodium lauryl sulphate as the key selective agent. citeturn521074search1turn521074search3

Coliform bacteria ferment lactose with production of acid and gas within the expected incubation period, and gas captured in a Durham tube provides the classical presumptive positive signal. Sodium lauryl sulphate improves selectivity by inhibiting much of the accompanying non-coliform flora, particularly Gram-positive organisms. citeturn521074search0turn521074search1

This makes LSB especially useful as the first-stage presumptive broth before confirmatory or differential coliform tests.

• Presumptive detection of coliforms in water, effluent, and sewage by MPN methods
• Routine water microbiology and sanitary quality assessment workflows
• Detection of coliform bacteria in dairy products and food samples
• Presumptive test step before confirmatory coliform or E. coli procedures
• General laboratory use in APHA- and ISO-associated coliform testing contexts

Typical Composition (per Liter)

Typical preparation falls around 35.6–36.5 g/L with final pH about 6.8 ± 0.2 at 25 °C. citeturn521074search1turn521074search3

Interpretation Logic

Medium	Primary Role	Strength	Limitation	Best Use
Lauryl Sulphate Broth (LSB)	Presumptive coliform detection	Strong routine fit for MPN and Durham tube workflows	Usually requires confirmatory follow-up	Water, dairy, food, sewage, effluent testing
Lactose Broth	Alternative presumptive medium	Simple and established	Less selective than LSB	Traditional presumptive methods
Brilliant Green Bile Broth	Confirmatory coliform test	Higher selectivity in confirmatory stage	Not ideal as first presumptive broth	Confirmation workflows
M-Endo / membrane filter systems	Membrane filtration and plating	Direct colony recovery after enrichment or filtration	Different workflow from tube fermentation	Membrane filter coliform methods

Commercial Positioning: A high-utility staple medium for routine coliform screening where consistency, clarity of interpretation, and method compatibility matter most.

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