Cat. no. C6520 CRITERION™ Oxford Listeria Agar Base 115gm
Cat. no. C6521 CRITERION™ Oxford Listeria Agar Base 500gm
Cat. no. C6522 CRITERION™ Oxford Listeria Agar Base 2kg
Cat. no. C6523 CRITERION™ Oxford Listeria Agar Base 10kg
Cat. no. C6524 CRITERION™ Oxford Listeria Agar Base 50kg


Hardy Diagnostics CRITERION™ Oxford Listeria Agar Base is used for the selective isolation of Listeria monocytogenes from food.

This dehydrated culture medium is a raw material intended to be used in the making of prepared media products, which will require further processing, additional ingredients, or supplements.


Listeria spp. are microaerophilic, gram-positive regular, short motile rods or coccobacilli that are asporogenous, non-encapsulated, and non-branching. Motility is best observed at 20-25ºC. Listeria monocytogenes is a pathogenic organism for humans and a large number of animal species. The members of the population most at risk are neonates, the elderly and those compromised by pregnancy or an underlying illness such as malignancy, alcoholism or some condition which requires immunosuppressive procedures. Intrauterine infection of the fetus results in death, or an acutely ill infant with a septic disseminated form of listeriosis. Papular lesions of the skin may be found in listeriosis of the newborn. A similar cutaneous form has been reported in veterinarians working with infected animals.(1,2)

A common vehicle for Listeria monocytogenes is pasteurized milk; since the induction of the Pasteurized Milk Ordinance in 1924, there have been fewer reported cases of milk contaminants other than Listeria spp. In Massachusetts in 1983, pasteurized milk spread Listeria monocytogenes to forty-nine people, 14 of which died of septicemia. Another incidence in California in 1985, was due to contamination of a soft Mexican cheese which caused 85 deaths of 300 infected patients. This led to a re-evaluation of pasteurization and aging techniques; however, the ability of L. monocytogenes to grow between 4 and 10ºC. and over a wide pH range (4.4-9.6) complicates the issue. The most effective containment still involves post-pasteurization pathogen detection.(3)

Other types of food that have been found to contain Listeria species as a contaminant are raw milk, raw vegetables, fish, poultry, and both fresh and processed meats. Ice cream has also served as a vehicle of transmission and in 1994 shrimp from a party in New York City infected ten people including two pregnant women. The CDC recommends, for immunocompromised, pregnant or elderly individuals, that foods to avoid are: soft cheeses, cold cuts and salami. There are also some reports of nosocomial infections of Listeria monocytogenes usually among infants or immunosuppressed adults.(1)

Listeria monocytogenes is ubiquitous in nature and has been isolated from soil, mud, sewage, decaying vegetation, silage, feces, and river water. Many animal species are vulnerable to infection by Listeria species and some lactating mammals can function as carriers (with no visible symptoms) while still excreting the organisms in their milk. Sheep, cattle and goats have also been found to shed Listeria monocytogenes in their feces. Listeriosis was caused by a meat product (hot dogs) in 1999 in the United States when 101 infections caused 21 deaths. Other contaminated foods include: coleslaw, pate, jellied pork tongue, cooked chicken and smoked mussels.(4)

The Oxford formulation contains lithium chloride which negatively affects the growth of enterococci. The Columbia Agar Base provides amino acids, carbon, vitamins and nitrogen. The esculin in the media is hydrolyzed by Listeria spp. and the resulting compound reacts with ferric ions (from the ferric ammonium citrate) to produce 6,7-dihydroxycoumarin and blackening of the media surrounding the colonies. Agar is used in solidification of the media.

Selectivity is enhanced by adding various antimicrobial agents to the base. Adding these agents into Oxford Medium Base will completely inhibit gram-negative organisms and most gram-positive organisms after 24 hours of incubation. The combinations available are the Oxford Medium formulation and the Modified Oxford Medium formulation. The Oxford Medium formulation contains cycloheximide, colistin sulfate, acriflavine, cefotetan and fosfomycin (available as Oxford Antimicrobic Supplement), The Modified Oxford Medium formulation contains moxalactam and colistin sulfate (available as Modified Oxford Antimicrobic Supplement).


Gram weight per liter: 57.5gm/L
Columbia Agar Base 39.0gm
Lithium Chloride 15.0gm
Esculin 1.0gm
Ferric Ammonium Citrate 0.5gm
Agar 2.0gm

Final pH 7.2 +/- 0.2 at 25ºC.

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


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 light beige.

Store the prepared culture media at 2-8ºC.



1. Suspend 57.5gm of the dehydrated culture media in 1 liter of distilled or deionized water.

2. Heat to boiling and mix to dissolve completely.

3. Sterilize in the autoclave at 121ºC. for 10 minutes.

4. Cool to 45-50ºC. in a waterbath.

5. Aseptically add selective supplements as desired.


For information on procedures and interpretation of results, consult listed references or refer to the prepared media Instructions for Use (IFU) for Cat. No. G46.


Since Listeria spp. other than L. monocytogenes can grow in these media, an identification of L. monocytogenes must be confirmed by biochemical and serological testing.

Use freshly prepared antimicrobial agent solutions or aliquot portions and store at -20 degrees C. or below.

Poor growth and a weak esculin reaction may be seen after 40 hours incubation for some enterococci.


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


Test Organisms Inoculation Method* Incubation Results
Time Temperature Atmosphere
Listeria monocytogenes
ATCC ® 7644
A 24-48hr 35°C Aerobic Growth; blackening of media around colonies
Escherichia coli
ATCC ® 25922
B 24-48hr 35°C Aerobic Partial to complete inhibition**
Staphylococcus aureus
ATCC ® 25923
B 24-48hr 35°C Aerobic Partial to complete inhibition**

User Quality Control


CRITERION™ Oxford Listeria Agar Base powder should appear homogeneous, free-flowing, and light beige in color. The prepared media should appear very slightly to slightly opalescent, and light to medium amber in color.


1. Koneman, E.W., et al. Color Atlas and Textbook of Diagnostic Microbiology, J.B. Lippincott Company, Philadelphia, PA.

2. Jorgensen., et al. Manual of Clinical Microbiology, American Society for Microbiology, Washington, D.C.

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

4. APHA Technical Committee on Microbiological Methods for Foods. Compendium of Methods for the Microbiological Examination of Foods, APHA, Washington, D.C.

5. Anderson, N.L., et al. Cumitech 3B; Quality Systems in the Clinical Microbiology Laboratory, Coordinating ed., A.S. Weissfeld. American Society for Microbiology, Washington, D.C.

6. U.S. Food and Drug Administration. Bacteriological Analytical Manual. AOAC, Arlington, VA.

ATCC is a registered trademark of the American Type Culture Collection.