CAT Nº: 1522
Tryptose
Lactose
Sodium Chloride
20.00 Dipotassium Phosphate
5.00 Bile Salts nº 3
5.00 Monopotassium Phosphate
4.00
1.90
1.50
Suspend 37.4 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Dispense in tubes with Durham gas collecting vials for gas detection and boil for 5 minutes. Sterilize in autoclave at 121°C for 15 minutes. DO NOT OVERHEAT. The prepared medium should be stored at 2 - 8 °C. The color is clear amber.
The dehydrated medium should be homogeneous, free-flowing and clear beige in color. If there are any physical changes, discard the medium.
EC MEDIUM was developed by Hajna and Perry, for the selective identification of coliform bacteria and Escherichia coli in water, foodstuffs and other materials. It is recommended by ISO 7251, for the enumeration of E.coli
with MPN tecnique.
This medium improves the detection methods of the coliform group, in particular of E.coli, and is used to investigate drinking water, wastewater treatment systems and generally for water-quality monitoring, as well as shellfish and other foods. It is used in many Standard Methods for Food and Water testing.
The medium can be used at 35 ± 2°C for detection of coliform organisms or at 44.5°C for isolation of E. coli.
The Bile salts act as selective agent inhibiting Gram-positive bacteria, bacilli and enterococci but allowing E. coli to develop. The Potassium salts have a high buffering capacity. Tryptose provides the nutrients for growth and Lactose is the fermentable carbohydrate as carbon and energy source. Sodium chloride maintains the osmotic balance.
Inoculate sample into tubes and incubate at 37°C for 24 hours. Lactose fermentation with gas production is evidence of the presence of coliforms .
If growth from positive tubes is re-inoculated and re-incubated at 44.5°C for 24 hours, and yields positive growth, confirmation of E. coli can then be made by using the appropriate biochemical tests (indole, citrate, etc.).
Formation of gas at 37°C …… coliforms .
Formation of gas at 37°C & 44.5°C …….. E. coli.
The following results were obtained in the performance of the medium from type cultures after incubation at a temperature of 44.5 ± 2ºC and observed after 24 ± 2 hours.
Microorganisms Growth Gas production
Bacilus subtilis ATCC 6633
Enterobacter aerogenes ATCC 13048
LABORATORIOS CONDA, S.A.
Inhibited
Inhibited
-
-
1

Escherichia coli ATCC 25922
Enteroococcus faecalis ATCC 19433
Good
Inhibited
+
-
According to ISO 11133 24-48h/44±1 ° C (Productivity, Selectivity)
Microorganisms
Inoculum
(cfu/ml)
Productivity
Qualitative
Escherichia coli ATCC 8739
Escherichia coli ATCC 25922
10-10 2
10-10 2
Turbidity (2) and gas in Durham tube
Turbidity (2) and gas in Durham tube
10 4 -10 6 Pseudomonas aeruginosa ATCC 27853
Reference media TSA
Selectivity
Qualitative
No growth
Hajna and Perry 1944 A.P.H.A.
Ray B. 1986 Impact of bacterial injury and repair in food microbiology. Its past, present and future J. Food Prot.
ISO 7251 Microbiology -- General guidance for enumeration of presumptive Escherichia coli -- Most probable number technique
ISO
25ºC
Once opened keep powdered medium closed to avoid hydration.
2ºC
LABORATORIOS CONDA, S.A.
2