Ingredients per liter of demineralized water:

Peptone 190 (Pancreatic Digest of Gelatin) 5.0 g
Beef Extract 3.0 g
Lactose 5.0 g

pH 6.7 + 0.2 at 25C


Lactose Broth is used in the detection and/or verification of the presence of coliform organisms in samples of water and dairy products.


Lactose Broth is prepared according to the formulation specified by the American Public health Association for use as a fermentation broth medium in the microbiological analysis of milk and milk products and water. The broth is used to detect and/or verify the presence of lactose fermenting, gram-negative, non-sporeforming bacilli in these substances.

In the examination of milk and milk products, lactose broth is recommended for use in the completion test to verify the presence of coliform bacteria. The presence of these organisms in milk or milk products is suggestive of unsanitary production9 processing and/or storage conditions or practices.3

The A.P.H.A. recommends the use of Lactose Broth fermentation tubes throughout the multitube fermentation technique to determine and confirm the presence of coliforms in water other tIian drinking water. This procedure is used to estimate the relative density of bacterial contamination or to determine the source of pollution.4

In preparation of the medium for use with inoculum of 1.0 ml volume or more, precautions must be observed to mantain the concentration of ingredients in the final mixture in line with that in the standard medium.


Suspend the specified quantity of medium given in chart below in 1000 ml distilled water. Mix thoroughly. Heat to boiling with frequent agitation to completely dissolve the medium. Dispense into appropriate size fermentation tubes or bottles. Sterilize by autoclaving at 121C for 15 minutes.

Inoculum ml Amount of Medium in tube ml Volume of Medium + Inoculum ml Dehydrated Medium Required grams/liter
1 10 or more 11 or more 13
10 10 20 26
10 20 30 19
100 50 150 39