Cultural Characteristics of Mycobacterium tuberculosis
- Culture is the gold standard for laboratory confirmation of Tuberculosis.
- Growing bacteria are required to perform drug-susceptibility testing and genotyping.
In Lowenstein-Jensen (LJ) medium
- It is an egg based medium and growth is quite slow.
- It takes 6-8 weeks to get visual colonies on this type of media.
- Colonies are non-pigmented, dry, rough, raised, irregular with wrinkled surface
- They are creamy white initially, becoming yellowish or buff colored on further incubation.
- Growth is eugonic (grows more luxuriantly in culture).
- Optimum temperature is 35-37°C and optimum pH is 6.4 to 7.
- It is an obligate aerobe.
- Increased carbon dioxide (5-10%) enhances the growth of Mycobacterium tuberculosis.
- 5% Glycerol also stimulates the growth.
- LJ media contain inhibitors to keep contaminants from out-growing Mycobacterium tuberculosis.
- The green color of the medium is due to the presence of malachite green which is one of the selective agents to prevent growth of most other contaminants.
- A faster result can now be obtained using Middlebrook medium or BACTEC.
Other Culture Media used for Mycobacterium tuberculosis
- Egg-based – Petragnini medium and Dorset medium
- Middlebrook 7H10 Agar
- Middlebrook 7H11 Agar
- Blood based – Tarshis medium
- Serum based – Loeffler medium
- Potato based – Pawlowsky medium
- Dubos’ medium
- Middlebrook 7H9 Broth
- Proskauer and Beck’s medium
- Sula’s medium
- Sauton’s medium