CHROMOGENIC COLIFORM AGAR
Chromogenic powdered and ready to use medium for the simultaneous detection of coliforms and Escherichia.
Code: CB1/2992
Typical formula g/l
| Tryptose | 10.00 |
| Tryptophan | 0.10 |
| Peptone mix | 5.00 |
| Yeast extract | 3.00 |
| Sodium chloride | 5.00 |
| Bile salts no.3 | 1.50 |
| IPTG | 0.10 |
| X-GLUC | 0.06 |
| Salmon GAL | 0.15 |
| Agar | 13.00 |
pH 7.0 +/- 0.2
Directions
Suspend 37.9 g in 1000 ml of cold distilled water. Boil until complete dissolution. Distribute and autoclave at 115°C for 15 minutes. For flasks; dissolve the contents of the bottle by boiling in a temperature controlled water batch. Cool to 50°C and distribute into sterile petri dishes.
Description
Chromogenic Coliform Agar is a selective and differential medium for the simultaneous detection of E. coli and coliform bacteria in waters and foods. The medium is made selective by the presence of bile salts; the differentiation between coliforms and E. coli is given by the presence of Salmon-GAL, a chromogenic substrate for the detection of β-galactosidase and X-GLUC, a chromogen substrate for the detection of β- glucuronidase. Salmon-GAL is hydrolysed by coliforms releasing a salmon colour pigment; this reaction is strengthened in the medium by the presence of IPTG (isopropil-b-D-thiogalactopyranoside). X-GLUC is hydrolysed, among enterobacteria, by E. coli, and by a few other strains of Salmonella and Shigella releasing a blue pigment. The presence of tryptophan in the medium allows testing the indole directly onto the colonies by adding Kovac’s Reagent, for the confirmation of E. coli.
Method
Carry out the simultaneous detection of coliform bacteria and E. coli, following the usual methods with surface streaking, poured plate or MF techniques and with incubation at 37°C for 18-24 hours: The colonies appearance is the following: Escherichia coli: dark blue colonies, indole positive Coliforms (other than E. coli); salmon coloured colonies. Proteus: colonies with bright brown halo. Other Enterobacteriaceae: colourless colonies. Gram-positive bacteria are usually inhibited. The Indole test is carried out by adding about 1ml of Kovac’s Reagent to the colonies and observing the formation of a red colour within 1-2 minutes.
User quality assurance (24 h-37°C)
Productivity control
E.coli ATCC 25922: growth, dark blue colonies, indole positive
Specificity control
E.aerogens ATCC 13048: growth, salmon colonies
Selectivity control
E.faecalis ATCC 19433: inhibited
Storage
Dehydrated medium: 2-8°C
User prepared plates: 7 days at 2-8°C
User prepared flasks: 1 month at 2-8°C