Listeria monocytogenes is responsible for an estimated 1,600 illnesses and 260 deaths in the United States (U.S.) annually and is ranks third in total number of deaths among food borne bacterial pathogens, with fatality rates exceeding even that of Clostridium botulinum and Salmonella.
Listeria monocytogenes is a gram positive facultative anaerobic pathogenic bacteria causing the infection Listeriosis. It can grow and reproduce inside the host’s cells and is one among the most virulent foodborne pathogens, with 20 to 30% of foodborne listeriosis infections in high-risk individuals which may be fatal.
Other species of listeria such as Listeria seeligeri, Listeria welshimeri and Listeria ivanovii have been related with animal diseases but Listeria monocytogenes is the only genus of listeria pathogenic to man.
Listeria Oxford Medium base with supplements is a selective growth media recommended for isolation of Listeria species from clinical and food specimen specimen based on the formulation described by Curtis et al.
Principle of Listeria Oxford Medium base
- The columbia Agar Base provides provides amino acids, carbon, vitamins and nitrogen and other essential nutrients.
- 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 for the solidification of the media.
- Lithium chloride, colistin, cycloheximide, acriflavine, and fosfomycin are incorporated as selective agents to inhibit the growth of most gram negative and most gram positive organisms after 24 hours of incubation.
Composition of Listeria Oxford Medium base
The following ingredients are used for the composition a typical Listeria oxford medium base
|Columbia Agar Base||39.0|
|Ferric Ammonium Citrate||0.5|
|Demineralized Water||1000.0 mg|
|Final PH at Temperature (25°c)||pH 7.2 ± 0.2|
* Adjusted the composition as required to increase selectivity of the media
VIAL OF LISTERIA SELECTIVE SUPPLEMENT (OXFORD FORMULATION) ADDITIONAL INGREDIENTS (500mg)
|Colistin sulphate||10.0 mg|
VIAL OF MODIFIED LISTERIA SELECTIVE SUPPLEMENT (OXFORD) ADDITIONAL INGREDIENTS (500mg)
|Amphotericin B||10.0 mg|
|Colistin sulphate||20.0 mg|
How to Prepare Listeria Oxford Medium base
The preparation of Listeria oxford Agar depends on each laboratory workload or the numbers of culture plates available. Anyway, note that a standard Petri dish is equivalent to 20ml when poured completely.
- Suspend 57.5gm of the dehydrated culture media in 1 liter of distilled or deionized water.
- Heat to boiling and mix to dissolve completely.
- Sterilize in the autoclave at 121ºC. for 10 minutes.
- Cool to 45-50ºC. in a waterbath.
- Aseptically add the above selective supplements as desired.
NB: It is advisable not to prepare large volumes that will require prolonged heating, thereby producing precipitate in the process.
NB: It is also advisable to incubate a petri dish for 24 hour for quality control in order to avoid wastage of resources and ease early detection of contamination after the preparation.
Appearance of Medium after preparation
It appears dark amber clear to slightly opalescent gel with a blue cast forms in Petri plates
Type of Inoculums
- water samples
- Vaginal and urethral discharges
Plate reading and Colonies morphology on Listeria Oxford Medium base
|Listeria monocytogenes ATCC 19111||Aerobic, up to 48 h at 33-37°C||positive reaction, blackening of medium around the colony|
|Staphylococcus aureus ATCC 25923||Aerobic, up to 48 h at 33-37°C||Partial to complete inhibition|
|Escherichia coli ATCC 25922||Aerobic, up to 48 h at 33-37°C||Partial to complete inhibition|
Note that colonies presumptively identified as Listeria monocytogenes must be confirmed by biochemical and serological testing
- Listeria spp. other than Listeria monocytogenes may grow on Listeria Oxford Agar.
- Enterococci may grow on Oxford Agar and exhibit blackening of the agar such colonies require differentiation from Listeria spp. using additional biochemical testing.
- This test is only part of the overall scheme for identification of Listeria monocytogenes. Additional biochemical and serological testing is required for definitive identification of isolate as Listeria spp.
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- Curtis G. D. W., Mitchell R. G, King A. F., Griffin E. J., 1989,Lett. Appl. Microbiol.,8:95
- Van Netten P., Peroles I., Van de Mosdik A., Curtis G. D. W., Mossel D. A. A, 1988, Int. J. Food Microbiol., 6:187.
- Hayes P. S, Feeley J. L, Groves L. M, Ajello G. W. and Fleming D. W, 1986, Appl. Environ. Microbiol., 51:438.
- Fernandez G. J. F., Dominguez R. L., Vazzuez B. J. A., Rodriguez F.E. F., Briones D. V., Blanco L. J. L., Suarez F. G., 1986, Can. J. Microbiol., 32:149.
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