Mycobacterium (Murray 3rd Ed pp 319)

This is a non-motile, non-spore forming and aerobic bacilli genus. The cell wall is rich in lipids, making it resistant to many disinfectants and laboratory stains. Due to the complexity of the cell wall, some bacteria only divides every 12-24 hrs therefore requiring many weeks of incubation, whilst others of the same genus require only 3 days.

The stain most commonly used is the Ziehl-Neelsen – acid fast – decolourisation is not possible once stain is established. The different types of species is identified by growth temperature, rate of growth and whether they are:

• Photochromogens: pigment prod in light

• Scotochromogens: pigment in light + dark

• Nonchromogens: no pig prod

Mycobacteria

This can be divided into two main groups:

• M TB (Mycobact. Tuberculosis complex)

  • Mycobact. Tuberculosis; M bovis; M africanum

• PPEM (Potentially pathogenic environment mycobacteria)(Atypical mycobacteria; runyan groups)

  • 95% are Mycobact. Avium intracellulare

Category: Microbiology Notes