Lab mycobacterium

Lab-2- Practical bacteriology

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
- The most human pathogens are:
- Mycobacterium tuberculosis causes tuberculosis (TB)
- Mycobacterium leprae causes leprosy.
- Mycobacterium avium -intracellulare (M avium complex, or MAC).
- Other atypical mycobacteria

Mycobacterium tuberculosis
- It is rod, nonmotile acid fast staining bacteria
- It is causes tuberculosis (TB) and spread by aerosols
- It is obligate aerobe
- It is grow best at 37oC temp
- 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

Diagnosis

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


2- Microscopy (Morphology identification)

- Mycobacteria cannot be classified as gram +ve or -ve.
- Ziehl-Neelsen staining is employed for identification of M.tuberculosis.



Acid-fast staining of sputum samples

2- Cultivation

- A Specimens from sputum decontamination with NaOH used for culturing
- Two media are used to grow MTB Lowenstein-Jensen medium and Middlebrook s medium. MTB colonies are small and buff colored when grown on either medium. Both types of media contain inhibitors that inhibit growth of contaminating bacteria and allow growth of M. tuberculosis.

Tuberculin Test
It is used for detection of specific (anti TBC) cell immunity(delayed cell hypersensitivity reaction). A Purified Protein Derivative (PPD) of cell wall of tubercle bacilli doses (5 (TU) Tuberculin Units) is obtained and inoculated into the intradermal layer.
- The skin test should be read 48 or 72 hours later.
- An individual who has had a primary infection with tubercle bacilli develops induration, edema, and erythema in 48-27 hours.



TB skin test - injection of M. tuberculosis proteins (tuberculin)

M. leprae

The diagnosis of leprosy is based on the clinical, and histologic examination of biopsy specimens taken from lepromas or other skin lesions. A pattern of inflammation plus the presence of acid-fast bacilli is presumptive evidence of infection with M leprae


Mycobacterium leprae