Modified Thayer-Martin Agar: Composition, preparation, uses and colony characteristics

Thayer-Martin agar medium is a selective medium used for the isolation of gonococci (Neisseria gonorrheae)  from specimen containing a mixed flora of bacteria and/or fungi e.g. urogenital specimen. Modified Thayer-Martin (MTM) agar is a GC agar base containing vancomycin, colistin, nystatin, and trimethoprim lactate (VCNT). Selective isolation of Neisseria gonorrhoeae is achieved with suppression of most other gram-negative diplococci, gram-negative bacilli, gram-positive organisms, and yeast.

Neisseria gonorrhoeae

Thayer-Martin medium contains antimicrobials which inhibit the growth of organisms other than N. gonorrhoeae.

Most Neisseria strains have complex growth requirements.  Gonococci are not able to grow on common blood agar.

Media preparation

  1. Suspend 7.2 g of GC agar base in 100 ml distilled water in a flask. Mix thoroughly, heat with frequent agitation, and bring to a boil for 1 minute to completely dissolve the powder.
  2.  Autoclave the flask at 121°C for 15 minutes.
  3. Cool to 50°C in a water bath.
  4. Add 100 ml of warm distilled water to 2 g of soluble hemoglobin powder. Mix the powder with 5-10 ml of distilled water until a smooth paste is achieved. Gradually add the balance of water until the solution is homogenous. Continually stir the solution during the addition of water.  Alternatively, 100 ml ready-made 2% sterile hemoglobin solution, warmed to 50°C can be used.
  5. Autoclave the solution at 121°C for 15 minutes. Cool to 50°C in a water bath.
  6. Reconstitute lyophilized growth supplement containing NAD and hemin by aseptically transferring 10 ml of the accompanying diluent with a sterile needle and syringe. Shake to assure complete solution. After reconstitution, use immediately or store at 4°C and use within 2 weeks.
  7. Aseptically add 100 ml sterile hemoglobin solution and growth supplement to 100 ml of the GC agar base solution. Mix gently, but thoroughly, to avoid air bubbles in the agar.
  8. To the agar base solution, add the following ingredients:
    1. 3.0 µg/ml vancomycin
    2. 7.5 µg/ml colistin
    3. 12.5 units/ml nystatin
    4. 5.0 µg/ml trimethoprim lactate
  9. Dispense 20 ml into 15×100 mm Petri dishes. Allow the media to solidify and condensation to dry.
  10. Place the plates in sterile plastic bags and store at 4°C until use.

Culture and Isolation

  1. Specimen (urethral or endocervical) is directly inoculated in the culture plates (Swabs with plastic or wire shafts and rayon, Dacron, or calcium alginate tips is used to collect the specimen for the culture of gonococci).
  2. The inoculated culture plate should be promptly placed into a CO2-enriched (3%- 10%) environment and incubated at 35º-37º C.
  3. Small opaque, grayish-white to colorless, raised, glistening and smooth colonies are seen.

Quality control

Passing result: