Listeria Oxford Agar Principle, Composition, Preparation and Colonies Characteristics

Oxford_Agar MLTGEEKS

follow 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 go to link 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.
Also read  Pseudomonas aeruginosa : Morphology,Diagnosis and Cultural characteristics

Composition of Listeria Oxford Medium base

The following ingredients are used for the composition a typical Listeria oxford medium base

Ingredients Grams/Litres
Columbia Agar Base39.0
Lithium Chloride15.0
Esculin1.0
Ferric Ammonium Citrate0.5
Demineralized Water1000.0 mg
Final PH  at Temperature (25°c)pH 7.2 ± 0.2
source url * Adjusted the composition as required to increase selectivity of the media

VIAL OF LISTERIA SELECTIVE SUPPLEMENT (OXFORD FORMULATION) ADDITIONAL INGREDIENTS (500mg)

Cycloheximide400.0 mg
Colistin sulphate10.0 mg
Fosfomycin10.0 mg
Acriflavine4.5 mg
Cefotetan2.0 mg

go to link VIAL OF MODIFIED LISTERIA SELECTIVE SUPPLEMENT (OXFORD) ADDITIONAL INGREDIENTS (500mg)

Amphotericin B  10.0 mg
Colistin sulphate20.0 mg
Fosfomycin10.0 mg
Acriflavine5.0 mg
Cefotetan2.0 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

Listeria Oxford agar
Listeria Oxford agar

Type of Inoculums

  • Blood
  • Urine
  • faeces
  • Foods
  • water samples
  • Vaginal and urethral discharges
Also read  Egg Yolk Agar Base Selective and Differential Medium for the Isolation of Clostridium perfringens

Plate reading and Colonies morphology on  Listeria Oxford Medium base

OrganismsIncubation periodResults
Listeria monocytogenes ATCC 19111Aerobic, up to 48 h at 33-37°C positive reaction, blackening of medium around the colony
Staphylococcus aureus ATCC 25923Aerobic, up to 48 h at 33-37°CPartial to complete inhibition
Escherichia coli ATCC 25922Aerobic, up to 48 h at 33-37°CPartial to complete inhibition

Note that colonies presumptively identified as Listeria monocytogenes must be confirmed by biochemical and serological testing

Listeria Monocytogenesis 
( produces small black, grey or brown colonies that are surrounded by a black zone.)
Listeria Monocytogenesis
( produces small black, grey or brown colonies that are surrounded by a black zone.)
Listeria innocua
Listeria innocua
Listeria Monocytogenes
Listeria Monocytogenes

Possible limitation

  • 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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Reference

  • 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.
Also read  tryptone soya agar (soybean casein digest agar) Principles,composition and growth characteristics

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About the Author: Arthur Westmann

DEFFE ARTHUR (AMOEBAMANN) is the founder and author of MLTGEEKS and MLTEXPO.He’s from Cameroon and is currently a Final year State Medical Laboratory Technician (MLT MA). Beyond lab works, he’s a passionate internet user with a keen interest in web design and blogging. Furthermore He likes traveling, hanging around with friends and social networking to do in his spare time.

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