Löwenstein–Jensen medium

When grown on LJ medium, M. tuberculosis appears as brown, granular colonies (sometimes called "buff, rough and tough"). The medium must be incubated for a significant length of time, usually four weeks, due to the slow doubling time of M. tuberculosis (15–20 hours) compared with other bacteria.

The medium is named after the Austrian pathologist Ernst Löwenstein (1878–1950) and the Danish medical doctor Kai Adolf Jensen (1894–1971).

Composition

The usual composition as applicable to M. tuberculosis is:

• Malachite green
• Glycerol
• Asparagine
• Potato starch
• Coagulated eggs
• Mineral salt solution
  • Potassium dihydrogen phosphate
  • Magnesium sulfate
  • Sodium citrate

The original formulation included starch, which was later found to be unnecessary, so omitted.

Low levels of penicillin and nalidixic acid are also present in LJ medium to inhibit growth of Gram-positive and Gram-negative bacteria, to limit growth to Mycobacterium species only. Presence of malachite green in the medium inhibits most other bacteria. It is disinfected and solidified by a process of inspissation. Presence of glycerol enhances the growth of M. tuberculosis.

If the slopes are made on test tubes, they must be stored in cold and used within a month.

For cultivation of M. bovis, glycerol is omitted and sodium pyruvate is added.

The medium appears green, opaque, and opalescent.