Lauryl Sulfate Broth

Lauryl Sulfate Broth (LST Broth)

EMD Cat. No. 1.10266.0500/5007

500 g, 5 kg

Selective culture medium used as a presumptive test for coliform bacteria and for the selective enrichment of coliform organisms in the analysis of water, according to MALLMANN and DARBY (1941).

This medium complies with the APHA Recommendations for Water Examination (1998) and the ISO 5541-2 (1996) for milk and milk products.

Additives

Mode of Action	Preparation
Experimental Procedure and Evaluation	Quality Control
Typical Composition (g/liter)	Literature

ChemDat®

Mode of Action
The high nutrient quality and the presence of phosphate buffer in this medium ensure rapid growth and increased gas production of even "slowly lactose-fermenting" colifirm bacteria. Gas formation can be detected by using fermentation tubes. The lauryl sulfate largely inhibits the growth of undesired bacteria.

Preparation

Suspend 35.6 g/liter or more, dispense into test tubes fitted with DURHAM tubes, autoclave
(15 min at 121 °C).

pH: 6.8 ± 0.2 at 25 °C.

The prepared broth is clear and yellowish-brown.

Inoculum ml	Amount of Medium in Tube ml	Volume of Inoculum ml	Dehydrated Lauryl Sulfate Broth Required g/L	Broth Concen- tration
1	10 or more	11 or more	35.6	1-fold
10	10	20	71.2	2-fold
10	20	30	53.4	1.5-fold
10	10	30	106.8	3-fold
100	50	150	106.8	3-fold
100	35	135	137.1	3.85-fold
100	20	120	213.6	6-fold

Experimental Procedure and Evaluation
See 7661 Lactose Broth.
Incubation: up to 48 h at 35 °C (or 30 °C) aerobically.

Quality control


Test strains	Growth	Gas formation

Escherichia coli ATCC 25922	good / very good	+
Escherichia coli ATCC 11775	good / very good	+
Klebsiella pneumoniae ATCC 13883	good / very good	+
Citrobacter freundii ATCC 8090	good / very good	±
Salmonella typhimurium ATCC 14028	good / very good	-
Proteus vulgaris ATCC 13315	poor / good	-
Staphylococcus aureus ATCC 25923	none / poor	-
Enterococcus faecalis ATCC 33186	fair / very good	-
Micrococcus luteus ATCC 10240	none / poor	-

Typical Composition (g/liter)
Tryptose 20.0; lactose 5.0; sodium chloride 5.0; sodium lauryl sulfate 0.1; di-potassium hydrogen phoshate 2.75; potassium dihydrogen phosphate 2.75.

Literature

American Public Health Association, American Water Works Association and Water Pollution Control Federation: Standard Methods for the Examination of Water and Wastewater, 20th ed., Washington, 1998.
HAJNA, A.A., a. PERRY, C.A. Comparative study of presumptive and confirmative media for bacteria of the coliform group and for fecal Streptococci. Am. J. Publ. Health, 33; 550-556 (1943).
MALLMANN, W.L., a. DARBY, C.W.: Use of a lauryl sulfate tryptose broth for the detection of coliform organisms. Am. J. Publ. Health, 31; 127-134 (1941).
International Standardization Organization: Milk and milk products Enumeration of coliforms. Part 2: Most probable number technique at 30 °C. ISO/CD 5541-2 (1996).