CHROMOSENSE ECX - GLUC AGAR (E. coli AGAR)
A chromogenic medium for the detection of E. coli in water and foodstuff.
Code: CB1/605a
Typical formula g/l
Tryptone
20.00
Yeast extract
5.00
Bile salts No. 3
1.50
Disodium phosphate
5.00
Monopotassium phosphate
1.50
Sodium chloride
5.00
X-GLUC
0.06
Tryptophan
1.00
Agar
12.00
pH 7.0 +/- 0.2
Directions
Suspend 51g in 1000ml of cold distilled water. Heat to boiling, with agitation until complete dissolution and autoclave at 115°C for 15 minutes. Cool to 50°C and distribute into sterile petri dishes.
Description
ECX-GLUC Agar (Chromogenic E. coli), is a selective differential medium for the enumeration and immediate identification of Escherichia coli mainly in water samples by means of MF technique. It is also useful for the detection of E.coli in foodstuffs with surface inoculated plate or with poured plate technique. The medium contains bile salts for the complete inhibition of Gram-positive bacteria and X-GLUC (5-bromo-4-chloro-3-indolyl β -D-glucuronide) for the detection of β –glucuronidase enzyme. Among the Enterobacteriaceae only E. coli, together with some strains of Salmonella and Shigella, is a β -glucuronidase positive species, so cultivates on the plates with blue or green-blue colonies. β-glucuronidase negative bacteria grow with colourless colonies. It is also possible to carry out the rapid indole test by leaving a drop of Kovacs’ reagent onto the medium and observing the reagent turning to red.
Method
Membrane filtration method :
Filter the sample on a 0,45μ membrane and settle the last over the medium surface.
Tightly close the plate and Incubate at 44 (+/- 0,5)°C for 24 (+/-2) hours.
Count as E. coli all the blue or blue-green colonies, confirmed by indole test.
Poured plate method:
Pour 1ml of the decimal dilutions of the sample into the plates.
Add about 15ml of ECX-GLUC Agar pre-cooled to 48-50°C.
Mix well the inoculum with the medium.
Incubate at 44 (+/- 0,5)°C for 24 (+/-2) hours
Count as E. coli all blue or blue-green colonies, confirmed by indole test
Report the results as UFC/g considering the "dilution factor"
The medium can be inoculated even in surface, with the usual methods.
User quality assurance (44°C - 24hrs)
Productivity control
E.coli ATCC 25922: growth, blue-green colonies indole positive
Specificity control
S.typhimurium ATCC 14028: growth, colourless colonies indole negative
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
References
Delisle, G.J., Ley, A. (1989) J. Clin. Microbiol. 27, 778
Frampton, E.W., Restaino, L., Blazko, N. (1988) J. Food Proct. 51,402