LAURYL SULFATE BROTH (LAURYL TRYPTOSE BROTH – LTB) ISO 4831
CAT Nº: 1310
For the detection of coliforms in waters
FORMULA IN g/l
Tryptose
20.00
Dipotassium Phosphate
2.75
Sodium Chloride
5.00
Monopotassium Phosphate
2.75
Lactose
5.00
Sodium Lauryl Sulfate
0.10
Final pH 6.8± 0.2 at 25ºC
PREPARATION
Suspend 35.6 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent
agitation. Boil for one minute until complete dissolution. Dispense into tubes with Durham gas collecting tubes for gas
detection. Sterilize in autoclave at 121°C for 15 minutes. The prepared medium should be stored at 2-8°C. The color is
clear amber.
The dehydrated medium should be homogeneous, free-flowing and pale beige in color. If there are any physical
changes, discard the medium.
Note: Refrigerated broth is cloudy, but clears considerably at room or incubator temperatures. Clarity is not required for the
performance of the medium because only gas formation is considered significant.
USES
LAURYL SULFATE BROTH is a selective medium recommended for the enumeration of coliforms in water and dairy
products as well as for confirmatory tests of lactose fermentation with gas production by coliforms in foods. Another
advantage of this medium is that the indole test can be performed directly in the tube.
APHA1 recommends the use of Lauryl Tryptose Broth for the Most Probable Number Presumptive Test of coliforms in
waters, effluent or sewage, also as a confirmatory test of lactose fermentation with gas production for milk samples, and
for the detection of coliforms in foods. This broth was elaborated to promote a rich growth and high gas production from
small inocula of coliform organisms.
The coliform group is both aerobic and anaerobic, Gram-negative, non -pore forming, and ferment lactose producing
acid and gas at 35°C within 48 hours.
Tryptose in a 2% concentration improves the early growth phase of coliforms when compared to Casein peptone. The
buffered broth allows slow lactose fermenters to increase gas production in a shorter time.
Tryptose provides nitrogen, vitamins, minerals and amino acids essential for growth. Lactose is a fermentable complex
carbohydrate energy source. Potassium phosphates are the buffering agents, and Sodium chloride supplies essential
electrolytes for transport and osmotic balance. Sodium lauryl sulfate is the selective agent used to inhibit organisms
other than coliforms. Sporulating aerobic bacteria are completely inhibited.
Inoculate sample and incubate at 35 ± 2°C for 24 - 48 hours. After 24 hours, measure gas production in the Durham
fermentation tubes. If no gas has been formed and trapped in the inverted tube, reincubate and re-examine after a
further 48 hours.
1
LABORATORIOS CONDA, S.A.
www.condalab.com
MICROBIOLOGICAL TEST
The following results were obtained in the performance of the medium from type cultures after incubation at a
temperature of 35 ± 2°C and observed after 24-48 hours.
Growth
Gas production
Good
Good
+
+
Good
Good
Markedly Inhibited
+
-
Microorganisms
Enterobacter aerogenes ATCC 13048
Escherichia coli ATCC 25922
Escherichia coli ATCC 8739
Salmonella typhimurium ATCC 14028
Staphylococcus aureus ATCC 25923
Inoculum
(cfu/ml)
103-105
Recovery Rate
%
≥30
103-105
103-105
103-105
≥30
≥30
≥30
103
≤0.01
According to ISO 11133 (24 ± 2) h to (48 ± 2) h/ 30±1°C (Productivity, Selectivity)
Microorganisms
Inoculum
cfu/ml
Escherichia coli ATCC 8739
Escherichia coli ATCC 25922
Citrobacter freundii ATCC 43864
Productivity
Qualitative
Characteristic
reaction
10 -102
turbidity (2), Gas 1/3
Gas production and turbidity
10 -102
turbidity (2), Gas 1/3
Gas production and turbidity
turbidity (2), Gas 1/3
Gas production and turbidity
3
10 -10
Selectivity
Qualitative
4
Enterococcus faecalis ATCC 29212
10 / 10
6
Inhibited
Enterococcus faecalis ATCC 19433
10 4/ 106
Inhibited
4
BIBLIOGRAPHY
ISO 4831 Microbiology of food and animal feeding stuffs — Horizontal method for the detection and enumeration of coliforms — Most
probable number technique
APHA 1998. Standard Methods for the examination of water and wastewater, 20th Edition.
Association of Official Analitical Chemist. 1995. Bacteriological analytical manual, 8th ed. AOAC International, Gaithersburg, MD.
Association of Official Analytical Chemists. 1995. Oficial methods of analysis of AOAC International, 16th ed. AOAC International,
Arlington, VA..
ISO
STORAGE
25ºC
Once opened keep powdered medium closed to avoid hydration.
2ºC
2
LABORATORIOS CONDA, S.A.
www.condalab.com