Lowenstein Jensen medium

Lowenstein-Jensen medium is a type of growth medium specifically used in microbiology for the cultivation of Mycobacterium tuberculosis, the bacterium responsible for tuberculosis (TB). This medium provides a selective environment that favors the growth of mycobacteria over other bacteria due to its unique composition and the presence of inhibitors that suppress the growth of most contaminating organisms found in clinical specimens.

Composition

Lowenstein-Jensen medium consists of a base of eggs, malachite green, and glycerol, along with mineral salts and potato flour. The eggs provide a source of protein and nutrients, while malachite green acts as a selective agent, inhibiting the growth of many non-mycobacterial species. Glycerol is used as a carbon source by Mycobacterium tuberculosis, but some strains, particularly those of Mycobacterium bovis, do not grow well on glycerol and may require the addition of pyruvate.

Preparation

The preparation of Lowenstein-Jensen medium involves mixing the ingredients and then sterilizing the mixture using steam or an autoclave. After sterilization, the medium is allowed to cool and solidify in a slanted position, creating a large surface area for the inoculation of specimens.

Usage

To isolate Mycobacterium tuberculosis, a clinical specimen is typically spread onto the surface of the Lowenstein-Jensen medium and then incubated at 37°C in a carbon dioxide-enriched atmosphere. The medium is observed regularly for the growth of colonies, which can take several weeks due to the slow growth rate of mycobacteria. Colonies of Mycobacterium tuberculosis appear as rough, dry, and cream-colored.

Advantages and Limitations

One of the main advantages of Lowenstein-Jensen medium is its ability to selectively cultivate Mycobacterium tuberculosis from clinical specimens that contain a mixed flora of bacteria. However, the medium has several limitations, including a long incubation period required for visible growth and the inability to differentiate between different species of mycobacteria based on colony morphology alone.

Conclusion

Lowenstein-Jensen medium plays a crucial role in the diagnosis and study of tuberculosis. Despite its limitations, it remains a standard tool in the isolation and cultivation of Mycobacterium tuberculosis and other mycobacteria in clinical and research settings.

Lowenstein Jensen medium Resources
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