Lowenstein–Jensen (LJ) medium is a selective culture medium used for the cultivation and isolation of Mycobacterium species.
It was originally developed by Lowenstein, who incorporated Congo red and malachite green to inhibit the growth of unwanted bacteria.
The present formulation of LJ medium is a glycerated, egg-based medium that is based on Jensen’s modification.
In Jensen’s version, Congo red is eliminated, and a moderate concentration of malachite green is used instead.
The inclusion of malachite green helps prevent the growth of most contaminating organisms that may survive the specimen decontamination process.
This modified formulation not only maintains selectivity but also encourages the earliest possible growth of mycobacteria, making it suitable for diagnostic use.
Composition of LJ Medium
Lowenstein–Jensen (LJ) medium contains potato flour (potato starch) at 30.0 g, which serves as a source of nutrients and supports bacterial growth.
L-Asparagine (3.6 g) is included as a nitrogen source essential for the metabolism of Mycobacterium species.
Monopotassium phosphate (2.4 g) acts as a buffering agent and provides essential phosphorus for cellular processes.
Magnesium citrate (0.6 g) supplies magnesium ions that function as enzyme cofactors and support metabolic activity.
Malachite green (0.4 g) is added as a selective agent to inhibit the growth of contaminating bacteria while allowing mycobacteria to grow.
Magnesium sulfate (0.24 g) provides additional magnesium ions required for enzymatic reactions and cellular stability.
Glycerol (12 ml) is included as a carbon and energy source that enhances the growth of most Mycobacterium species.
Egg suspension (1000 ml) forms the base of the medium, providing proteins, lipids, and growth factors necessary for mycobacterial cultivation and giving the medium its solid consistency after inspissation.
Distilled water (600 ml) is used to dissolve and uniformly distribute all components of the medium.
For the cultivation of Mycobacterium bovis, glycerol is omitted because it inhibits its growth, and sodium pyruvate is added instead to support optimal growth of this species.
Principle of LJ Medium
L-Asparagine and potato flour serve as important sources of nitrogen and vitamins, supporting the metabolic requirements of mycobacteria.
Monopotassium phosphate and magnesium sulfate enhance the overall growth of the organism and also act as buffering agents to maintain a suitable pH of the medium.
Malachite green inhibits the growth of the majority of contaminating organisms that may survive specimen decontamination, while selectively encouraging the growth of Mycobacterium species.
Egg suspension provides essential fatty acids and proteins required for the metabolism and growth of mycobacteria.
Upon heating, the egg albumin coagulates, resulting in a solid surface that is suitable for inoculation and colony development.
Glycerol functions as a carbon source and promotes the growth of the human type tubercle bacillus, while being unfavorable for the growth of the bovine type.
Uses of LJ Medium
It is used for the diagnosis of mycobacterial infections by supporting the isolation and growth of Mycobacterium species from clinical specimens.
It is used for antibiotic susceptibility testing of isolated mycobacterial strains to assess their response to anti-mycobacterial drugs.
It is also used for differentiation of various Mycobacterium species based on colony morphology, growth rate, biochemical characteristics, and microscopic appearance.
Preparation of LJ Medium
Dissolve 37.3 g of Lowenstein–Jensen medium in 600 ml of distilled water containing 12 ml of glycerol.
Heat gently, if necessary, to ensure the medium is completely dissolved.
Autoclave at 121 °C for 15 minutes to sterilize the medium.
Under aseptic conditions, prepare 1000 ml of a uniform suspension of fresh eggs, taking care to avoid whipping air into the suspension during collection and mixing.
Aseptically mix the 1000 ml egg suspension with 600 ml of the sterile Lowenstein–Jensen medium that has been cooled to 50–60 °C, ensuring that air bubbles are avoided.
Dispense the prepared medium into sterile screw-cap test tubes.
Place the tubes in a slanted position and heat at 85 °C for 45 minutes to allow proper coagulation of the medium.
Colony Morphology on LJ Medium
Cultures on Lowenstein–Jensen (LJ) medium should be examined within 5–7 days after inoculation and then observed weekly for up to 8 weeks to detect slow-growing mycobacteria.
Typical colonies appearing on LJ medium are non-pigmented, rough, and dry in texture.
The green color of the medium is due to the presence of malachite green, which acts as a selective agent by inhibiting the growth of most contaminating organisms while allowing mycobacteria to grow.
Limitations of LJ Medium
For complete and accurate identification, it is recommended that biochemical and/or serological tests be performed on colonies obtained from pure cultures, as LJ medium alone is not sufficient for definitive identification.
Lowenstein–Jensen (LJ) medium requires incubation in an atmosphere containing 5–10% CO₂ for optimal recovery of mycobacteria; for unknown reasons, mycobacteria are not recovered efficiently in candle extinction jars.
Negative culture results on LJ medium do not rule out active mycobacterial infection, particularly in cases with low bacterial load or improper specimen handling.
Due to nutritional variation, some mycobacterial strains may grow poorly or fail to grow on LJ medium, making additional tests necessary for confirmation of Mycobacterium species.
References
Hardy Diagnostics. Lowenstein–Jensen (LJ) Medium.
Microbiology In Pictures. Educational resources on microbiological culture media.
Laboratory Info. Reference material on Lowenstein–Jensen medium.
Wong’s Virology. Standard textbook reference for mycobacterial culture and virology.
Medico Tips. Educational content related to microbiology and diagnostic media.
Dynamicro Labs. Manufacturer information on Lowenstein–Jensen medium.
E&O Laboratories Ltd. Product and technical information on LJ medium.
Sigma-Aldrich Co. LLC. Lowenstein–Jensen Medium Base (Product Code: L3910).
HiMedia Laboratories. Lowenstein–Jensen Medium (LJ Medium) product documentation.
BBL™ Mycobactosel™ L-J Medium. Product information and technical specifications.
Acumedia Manufacturers, Inc. Lowenstein–Jensen Medium (7245).
Wikipedia. General overview and background information on Lowenstein–Jensen medium.
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