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 (16.7.1894-2.5.1971).[2]
Composition
The usual composition[3] as applicable to M. tuberculosis is:
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 differentiating different species of Mycobacterium (by colony morphology, growth rate, biochemical characteristics, and microscopy)
Mycobacterium tuberculosis
Mycobacterium bovis
Eugonic, rough tough and buff
Dysgonic
Aerobic
Microaerophillic
Glycerol enhancement +
Glycerol enhancement -
Pyruvate enhancement +
Pyruvate enhancement -
Niacin production +
Niacin production -
Alternatives
Alternative culture media
While LJ medium is the most popular means of culturing mycobacteria, as recommended by the International Union against Tuberculosis, several alternative media have been investigated.[4]
Solid media
Egg-based – Petragnani medium[5] and Dorset medium
The chief limitation of culture-based techniques is the time it takes to culture positivity, which can be several months. Several new molecular technologies have emerged in recent years to secure more speedy confirmation of diagnosis.[citation needed]
