laboratory diagnosis of mycobacterium

Mycobacterium
General characteristics

- The mycobacteria are rod-shaped, aerobic bacteria that do not form spores. They do not stain readily, once stained they resist decolorization by acid or alcohol and are therefore called "acid-fast" bacilli. Has complex cell wall lipids contain mycolic acids and resistance to drying, acids, some germicides
- It is slow-growing and survive after ingestion by macrophages
- The most human pathogens are:
- Mycobacterium tuberculosis causes tuberculosis (TB)
- Mycobacterium leprae causes leprosy.
- Mycobacterium avium -intracellulare (M avium complex, or MAC).

Mycobacterium tuberculosis

- It is rod, nonmotile acid fast staining bacteria
- It is obligate aerobe
- Has waxy cell wall made up of fatty acids called mycolic acid and lipids account for 60% of cell wall weight and its responsible for many characteristic
- Acid fastness
.

Isolation and identification tubercle bacilli

1- A- Specimens: consist of fresh sputum and gastric contents.
B- Decontamination of specimens: Specimens from sputum decontamination from overgrowing contaminating flora with NaOH and used for acid-fast stains and for culture
- Ziehl-Neelsen staining is employed for identification of M.tuberculosis. It is characterized by acid-fastness i.e. acid-alcohol quickly decolorizes all bacteria except the mycobacteria.