CRITERION™ Deoxycholate lactose agar

Cat. no. C5560 CRITERION™ Deoxycholate Lactose Agar 85gm
Cat. no. C5561 CRITERION™ Deoxycholate Lactose Agar 500gm
Cat. no. C5562 CRITERION™ Deoxycholate Lactose Agar 2kg
Cat. no. C5563 CRITERION™ Deoxycholate Lactose Agar 10kg

INTENDED USE

Hardy Diagnostics CRITERION™ Deoxycholate Lactose Agar is recommended for the isolation and differentiation of gram-negative enteric bacteria. Also used for the enumeration of coliforms from water, wastewater, milk, and dairy products.(2-4)

SUMMARY

CRITERION™ Deoxycholate Lactose Agar, is a modification of Deoxycholate agar as described by Leifson(1) for the selective isolation and enumeration of intestinal pathogens. This medium contains citrate and sodium deoxycholate making it selective against gram-positive organisms. The addition of lactose to the medium makes it differential for coliforms based on lactose fermentaion.

FORMULA*

Gram weight per liter: 42.5gm/L
Lactose 10.0gm
Protease Peptone No. 3 5.0gm
Meat Peptone 5.0gm
Sodium Chloride 5.0gm
Sodium Citrate 2.2gm
Sodium Deoxycholate 0.5gm
Sodium Carbonate 0.1gm
Neutral Red 18.0mg
Agar 14.7gm

Final pH 7.1 +/- 0.1 at 25ºC.

* Adjusted and/or supplemented as required to meet performance criteria.

STORAGE AND SHELF LIFE

Store the sealed bottle(s) containing dehydrated culture medium at 2-30ºC. Dehydrated culture medium is very hygroscopic. Keep lid tightly sealed. Protect dehydrated culture media from moisture and light. The dehydrated culture media should be discarded if it is not free-flowing or if the color has changed from its original, homogeneous light beige/pink,

Store the prepared culture media at 2-8ºC.

PRECAUTIONS

METHOD OF PREPARATION FOR DEHYDRATED CULTURE MEDIA

1. Suspend 42.5gm of the dehydrated culture media in one liter of distilled or deionized water. Stir and heat to mix thoroughly.

2. Heat to boiling to dissolve completely. Avoid overheating. Do Not Autoclave.

3. Cool to 45-50ºC. and aseptically dispense into sterile containers.

PROCEDURE

Test samples using either the spread plate or pour plate technique as described in the literature.(2-4)

Incubate at 35-37ºC. for 18-24 hours. Observe plates for the presence of lactose fermentation.

INTERPRETATION OF RESULTS

Organisms which ferment lactose will appear as red colonies, non-lactose fermenters form colorless colonies. Coliform bacteria will produce pink colonies.

LIMITATIONS

MATERIALS REQUIRED BUT NOT PROVIDED

Standard microbiological supplies and equipment such as autoclaves, incinerators, and incubators, etc., are not provided.

QUALITY CONTROL

Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Escherichia coli
ATCC ® 25922
A 24hr 35°C Aerobic Growth, pink to red colonies with bile precipitate surrounding colonies
Klebsiella pneumoniae
ATCC ® 13883
A 24hr 35°C Aerobic Growth, pink to red colonies
Shigella flexneri
ATCC ® 12022
A 24hr 35°C Aerobic Growth, colorless colonies
Salmonella enterica
ATCC ® 14028
A 24hr 35°C Aerobic Growth, colorless colonies
Enterococcus faecalis
ATCC ® 29212
B 24hr 35°C Aerobic Partial to complete inhibition
Staphylococcus aureus
ATCC ® 6538
B 24hr 35°C Aerobic Partial to complete inhibition

User Quality Control

Physical Appearance

CRITERION™ Deoxycholate Lactose Agar powder should appear homogeneous, free-flowing, and pink/beige in color. The prepared medium should appear slightly opalescent, and pinkish-red in color.

REFERENCES

1. Leifson. 1935. New culture media based on sodium desoxycholate for the isolation of intestinal pathogens and for the enumeration of colon bacilli in milk and water. J. Path. Bact. 40:581.

2. American Public Health Association. Standard Methods for the Examination of Water and Wastewater, APHA, Washington, D.C.

3. American Public Health Association. Standard Methods for the Examination of Dairy Products, APHA, Washington, D.C.

4. Speck M. (Ed.), 1984, Compendium of Methods for the Microbiological Examination of Foods, 2nd ed., APHA, Washington, D.C.


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