This culture medium complies with the recommendations of the United States Pharmacopeia XXVI (2003), the European Pharmacopeia II, the International Organization for Standardization
(ISO) (1977, 1984), the International Dairy Federation (Internationaler Milchwirtschaftsverband) (1978) and the DIN Norms 10163 and 10178.
Mode of Action
This medium contains lithium chloride and tellurite to inhibit the growth of accompanying microbial flora, whereas pyruvate and glycine selectively stimulate the growth of staphylococci.
Staphylococcus colonies show two characteristic features when grown in this opaque medium (opaque, because of its egg-yolk content)
a. characteristic zones and rings are formed as a result of lipolysis and proteolysis,
b. reduction of tellurite to tellurium produces a black colouration.
The egg-yolk reaction and tellurite reduction are usually found to occur together with a positive coagulase reaction and can thus serve as an index for the latter.
STADHOUDERS et al. (1976) recommend that egg-yolk should be replaced with blood plasma, if coagulase-positive staphylococci are to be detected directly.
SMITH and BAIRD-PARKER (1964) recommend the addition of sulfamethazine to suppress the growth and swarming of Proteus species.
Typical Composition (g/litre)
Peptone from casein 10.0; meat extract 5.0; yeast extract 1.0; sodium pyruvate 10.0; glycine 12.0; lithium chloride 5.0; agaragar 15.0.
Also to be added:
Egg-yolk tellurite emulsion 50ml; if required, sulphamethazine 0.05 g/l.
Suspend 58 g in 0.95 litre, autoclave (15 min at 121 °C). Cool to 45-50 °C, mix in 50 ml Egg-yolk Tellurite Emulsion and, if required, 50 mg sulfamethazine/litre. Pour plates.
pH: 6.8 ± 0.2 at 25 °C.
The plates are opalescent and yellowish-brown in colour.
The ready-to-use culture medium can be stored in the refrigerator (approx. 4 °C) for up to 1 month.
Experimental Procedure and Evaluation
Dilute the sample material and spread thinly on the surface of the culture medium.
Incubation: 24-48 hours at 35 °C aerobically
|Appearance of Colonies||Microorganisms|
|Black, shiny, convex colonies
1-5 mm in diameter with a
narrow, white edge surrounded
by a clear zone 2-5mm wide.
Opaque rings within the clear
zones only appear after
48hours of incubation
|Black, shiny, irregular shape.
Opaque zone develop around
the colonies after 24hours.
|Growth sometimes: Very small,
brown to black, nor clear
|Dark brown, dull, clear zones
sometimes appear after
|White, no clear zones||Yeasts|