Tellurite Glycine Agar

Intended Use

Tellurite Glycine Agar is used with Tellurite Solution 1% for isolating coagulase-positive staphylococci.

Summary and Explanation

Coagulase-positive Staphylococcus aureus is well documented as a human opportunistic pathogen.1 Foods are examined for the presence of S. aureus and/or its enterotoxins to confirm that S. aureus is the causative agent of foodborne illness, to determine whether a food is the source of “staph” food poisoning and to determine post-processing contamination.2
Ludlam3 described a selective medium for the isolation of staphylococci. This medium was alkaline in reaction, contained mannitol, and lithium chloride with potassium tellurite as the
selective agents. Zebovitz, Evans and Niven4 modified Ludlam’s medium by adding glycine as a selective agent and adjusting the reaction of the basal medium to pH 7.2 instead of pH 9.6.
Tellurite Glycine Agar is prepared according to the formula of Zebovitz, Evans and Niven.4 The medium permits the isolation of coagulase-positive staphylococci from food, air, dust, soil and clinical specimens. Coagulase-negative staphylococci and other bacteria are markedly to completely inhibited.

Principles of the Procedure

Peptones are sources of nitrogen and amino acids in Tellurite Glycine Agar. Yeast extract is a vitamin source in this formulation. D-Mannitol is a source of fermentable carbohydrate for coagulase-positive staphylococci. Lithium chloride, glycine and potassium tellurite are the selective agents. Dipotassium phosphate is used to buffer the medium. Agar is the solidifying
agent.
Tellurite Solution is a sterile 1% solution of potassium tellurite, a differential agent. Coagulase-positive staphylococci reduce tellurite and produce black colonies.5

User Quality Control

Identity Specifications
Tellurite Glycine Agar
Dehydrated Appearance: Light beige, free-flowing, homogeneous.
Solution:                       6.25% solution, soluble in purified water upon
                                   boiling. Solution is amber, opalescent with
                                   precipitate.
Prepared Appearance:    Medium amber, opalescent with precipitate.
Reaction of 6.25%
Solution at 25°C:           pH 7.2 ± 0.2
Cultural Response
Tellurite Glycine Agar
Prepare the medium per label directions. Inoculate and incubate at 35 ± 2°C for 18-48 hours.

Formula

Tellurite Glycine Agar
Approximate Formula* Per Liter
Yeast Extract............................................................... 6.5 g
Soytone...................................................................... 3.5 g
Tryptone................................................................... 10.0 g
Glycine...................................................................... 10.0 g
D-Mannitol.................................................................. 5.0 g
Dipotassium Phosphate................................................ 5.0 g
Lithium Chloride.......................................................... 5.0 g
Agar ........................................................................ 17.5 g
*Adjusted and/or supplemented as required to meet performance criteria.

Directions for Preparation from Dehydrated Product

1. Suspend 62.5 g of the powder in 1 L of purified water. Mix thoroughly.
2. Heat with frequent agitation and boil for 1 minute to completely dissolve the powder.
3. Autoclave at 121°C for 15 minutes.
4. Aseptically add 10 mL Tellurite Solution 1% to the medium at 50-55°C. Mix well.
5. Test samples of the finished product for performance using stable, typical control cultures.

Procedure

For a complete discussion on the isolation and identification of coagulase-positive staphylococci from clinical specimens refer to appropriate procedures.1,6 For the examination of
staphylococci in foods refer to standard methods.2,7

Expected Results

Coagulase-positive staphylococci produce black colonies within 24 hours of incubation at 35°C.

Limitation of the Procedure

Occasional coagulase-negative staphylococci may produce small gray colonies, not readily confused with black coagulase-positive colonies.

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