Mycobacteria

Mycobacteria
It is curved rods, non-motile acid fast staining bacteria (e.g. Ziehl-Neelsen). Most mycobacteria are found in habitats such as water or soil. The cell wall contains complex waxes and glycolipids account for 60% of cell wall weight and its responsible for many characteristics: acid Fastness, antibiotic resistance, resistance to detergents, drying and acids.
Classification of mycobacterium
Mycobacteria are classified into members of the Mycobacterium tuberculosis complex (M tuberculosis, M bovis, M africanum, M microtii) cause the disease known as tuberculosis (TB) and nontuberculous species
Medically important Mycobacteria

- Mycobacterium tuberculosis complex
Mycobacterium tuberculosis ,
M.bovis, M.ulcerans
- Atypical Mycobacteriae – classification according Runyon
M.kansasi, M.marinum photochromatic
M.scrofulaceum scotochromatic
M.avium, M.intracelulare slowly growing non pigmented
M.fortuitum, M.chelonae quickly growing non pigment
e - Mycobacterium lepra

Mycobacterium tuberculosis
M. tuberculosis is an obligate aerobe, growing most successfully in tissues with a high oxygen content, such as the lungs. For this reason, causative agent of tuberculosis (TB). It is intracellular parasite, usually of macrophages, has a slow generation time of 12 to 18 hours (c.f. 20-30 minutes for Escherichia coli).

Pathogenesis and Immunity

Primary TB:
M. tuberculosis produces no toxins or enzymes that contribute to virulence. Bacterium inhaled into lungs, arrives at alveoli and phagocytosed by alveolar macrophages then replicate intracellularly and kill macrophage
Secondary reactivation TB:
– If the immune system becomes weakened, suppression of immune system (immunosuppressive drugs), old age, cancer, and HIV infection can lead to reactivation the tubercle opens may allow bacteria to break out of lesions, multiply, releasing the bacteria and the infection may develop into secondary TB.
– More severe symptoms developed
– Untreated secondary TB has a nearly 60 % mortality rate

Clinical Manifestations
Tuberculosis primarily affects the lower respiratory system and is characterized by a fever, chronic productive cough(often with blood), night sweats, weight loss malaise (loss of energy) and loss of appetite.


Figure(3) Ghon complex

Diagnosis

1- Diagnosis of active disease is based on clinical manifestations and chest X rays
2- Acid-fast staining of sputum for direct identification of acid-fast bacilli in specimen
3- Cultural isolation and biochemical testing
4- Mantoux test in vivo or tuberculin skin testing