CHINA BLUE LACTOSE AGAR

Code: CM0209

A standard, non-inhibitory solid medium for enumeration and differentiation of bacteria in dairy products.

Typical Formula*	gm/litre
Peptone	5.0
`Lab-Lemco’ powder	3.0
Lactose	10.0
Sodium chloride	5.0
China blue	q.s.
Agar	12.0
pH 7.0 ± 0.2 @ 25°C

* Adjusted as required to meet performance standards

Directions
Suspend 35g in 1 litre of distilled water. Boil to dissolve completely. Sterilise by autoclaving at 121°C for 15 minutes.

Description
China Blue Lactose Agar was formulated by Brandl and Sobeck-Skal¹. A standard, non-inhibitory solid medium for the differentiation and enumeration of bacteria in milk, proposed by the Methodenkommission fÏr Milchwirtschaft². The china blue serves as a pH indicator, to differentiate between lactose fermenters and non-lactose fermenters, but does not suppress the growth of cocci; therefore this medium may be used for the detection of streptococci and staphylococci as well as the coli-aerogenes group.

Plates may be streak-inoculated or decimal dilutions of milk may be added to the molten, cooled medium in a pour-plate technique.
After 18 hours incubation at 35°C colony appearances are:-

Colour	Micro-organisms
Blue	Lactose fermenters e.g. Escherichia coli and coliform bacteria: 3-4 mm diameter Staphylococci: 1 mm diameter Streptococci: 0.5 mm diameter
Colourless	Non-lactose fermenters e.g. Salmonella, Serratia, Proteus species and others

Storage conditions and Shelf life
Store the dehydrated medium at 10-30°C and use before the expiry date on the label.
Store the prepared medium at 2-8°C.

Appearance
Dehydrated medium: Straw / pale blue coloured, free-flowing powder
Prepared medium: Blue coloured gel