CHROMOSENSE CEC AGAR
A chromogenic and fluorogenic medium for the simultaneous detection of total coliforms and Escherichia coli in water and foodstuffs.
Code: CB1/805
Typical formula g/l
| Tryptose | 10.00 |
| Tryptophan | 1.00 |
| Peptone mix | 5.00 |
| Yeast extract | 3.00 |
| Sodium chloride |
5.00 |
| Bile salts No.3 | 1.50 |
| IPTG | 0.10 |
| X-GAL | 0.08 |
| MUG | 0.05 |
| Agar | 13.00 |
pH 7.4 ± 0.1
Directions
Suspend 38.8g in 1000ml of cold distilled water. Heat to boiling, stirring until complete dissolution. Sterilise in the autoclave at 115°C for 15 minutes. Pour into sterile petri dishes and use within one week.
Description
The detection and enumeration of faecal indicators is one of the main tests for estimating the microbiological quality of waters and foodstuffs. The usual methods require from 24 till 72 hours to get complete results, and give some false positive and false negative or doubtful results due to late or weak lactose metabolism. CEC Agar allows a quantitative detection in 18-24 hours of total coliforms and E.coli through a method based on the enzymatic hydrolysis of fluorogenic and chromogenic substrates by means of ß-galactosidase (ß-GAL) and ß-glucuronidase (ß-GLU).CEC Agar is prepared with a selective agar base, supplemented with 5-Bromo-4 chloro-3-indolyl-ß-D- galactopyranoside (X-GAL), 4-methylumbelliferil-ß-D-glucuronide (MUG), isopropyl-ß-D-thiogalactoside (IPTG) and Tryptophan. This medium allows the selective growth of Enterobacteriaceae and of a few other Gram-negative bacteria, being Gram positive inhibited by the selective agents present in the substrate.
Among Enterobacteriaceae, the coliforms have the beta-galactosidase enzyme, hydrolyse the X-GAL compound, and grow with blue green colonies; E. coli hydrolyses X-GAL and MUG with formation of umbelliferone, strongly fluorescent when the plates are observed under Wood’s lamp. The hydrolysis of X-GAL in enhanced by IPTG. The indole test can confirm the presence of E. coli by adding a drop of Kovacs’ reagent to the colonies.
Method
CEC Agar can be used with plating method for foodstuffs and with membrane filtration method for water samples. It is useful for the detection and enumeration of:
- E. coli and total coliforms in water and foodstuffs incubating at 35 or 37°C for 18-24 hours
- E. coli and faecal coliforms in water and foodstuffs incubating at 44°C for 18-24 hours
E. coli grows on the medium with blue-green colonies, fluorescent when observed under a Wood’s lamp, positive to indole test.
Coliform bacteria other than E.coli grow with blue-green colonies not fluorescent under Wood’s lamp.
User quality assurance (24hrs -37°C)
Productivity control
E.coli ATCC 25922: growth, blue-green colonies fluorescent under Wood’s lamp
Specificity control
K.pneumoniae ATCC 27736: growth, blue-green colonies not fluorescent under Wood’s lamp
Selectivity control
E.faecalis ATCC 19433: inhibited
Storage
Dehydrated medium: 2-8°C
User prepared plates: 1 month at 2-8°C
User prepared flasks: 3 months at 2-8°C
References
Damare, J.M., Campbell, D.F., Johnson, R. (1985) J. Food Sciences 50, 1736
Jermini, M., Domeniconi, F., Jaeggll, M., 1994. C-EC-Agar, a Modified mFC-Agar for the Simoultaneous Enumeration of Fecal Coliforms and E. coli in water samples. Letters in App. Microbiol. 19, 332-335