Mycobacterium Flashcards
Properties of mycobacteria
Non spore forming, aerobic rods.
Classification of mycobacteria
Tb complex
Mycobacterium Leprae
Atypical mycobacteria
TB complex
Mycobacterium tuberculosis
Mycobacterium Africanum
Mycobacterium bovis
Atypical mycobacteria
Photochromogenes
Scotochromogenes
Non chromogenes
Rapid Growers
Photochromogenes
Mycobacterium kansasii
Mycobacterium marinum
Scotochromogenes
Mycobacterium scrofulaceum
Non-chromogenes (they are non-pigmented or have light tan or buff
coloured colonies)
Mycobacterium avium-intracel/ulare complex
Mycobacterium ulcerans
Rapid growers (growth in <7days)
Mycobacterium fortuitum complex
Mycobacterium smegmatis
Mycobacterium phlei
General characters of mycobacteria
Slender, straight or slightly curved rods with rounded ends.
Acid-fast, non-sporogenous and non-capsulated.
Z -N staining is employed for identification.
Obligate aerobes. Increased CO2 tension enhances growth.
Highly resistant to drying.
Constituents of the cell wall
Lipids
Proteins
Polysaccharides
Lipids
Mycobacteria are rich in lipids. These include mycolic acids (long
chain fatty acids C7s-C90), waxes and phosphatides. Lipids are largely bound
to proteins and polysaccharides. Muramyl dipeptide from peptidoglycan
complexed with mycolic acids can cause granuloma formation,
phospholipids induce caseous necrosis. Lipids are to some extent responsible
for acid fastness.
Protein
Contains several proteins, those bound to a wax fraction upon injection can induce tuberculin sensitivity
Polysaccharides
Can induce an immediate hyper sensitivity reaction and can serve as antigens
Virulence factors
Cord factor
Sulfatides
Lipoarabinomannan
Heat shock protein
Cord factor
It is a surface glycolipid
Inhibits migration of leucocytes causes chronic granuloma, and can serve as an immunologic adjuvant.
Sufatides
Surface glycoprotein
Prevents fusion of phagosomes with lysosomes in microphage and allowing the bacterium escape the degradative action of lysosomal enzymes
Lipoarabinomannan
Heteropolysaccharides
Inhibits microphage activation by interferon gamma
Induces macrophage to secrete TNF ALPHA WHICH CAUSES FEVER, WEIGHT LOSS, AND TISSUE DAMAGE.
Induces IL 10 which suppresses mycobacteria induced Tcell poliferation
Heat shock protein
Highly immunogenic
Pathogenesis
After inhalation of bacteria ~~~~~ reach alveolar space and phagocystosed by alveolar macrophage ~~~~~~~ spread to hylar lymph nodes and into blood stream ~~~~~~ non specific inflammatory response at initial focus ~~~~~~ delayed hypersensitivity ~~~~~~~ granulomatous formation ~~~~~~ Ghons complex.
Primary infection Vs secondary infection
Primary infection. Secondary Infection
Lesion: Small Large
Lymphatic
Involvement: Yes Minimal
Cavity
Formation: Rare. Frequent
Tuberculin
Reactivity : initially negative Positive
Site : any part of lung
Usually lower lobe Apical region
Local spread : Uncommon. Frequent
Types of tuberculous infection
Pulmonary
Exttrapulmonary :
TB plueral effusion
Tuberculosis menigitits
miliary TB
Renal and urogenital TB
Bone and joint TB
TB enteritis
Lab Diagnosis of TB
Tuberculin Test
Intradermally 0.1 to 5 PPD tuberculin
Wheal: 6mm to 10mm
48 to 72 hours after injection
Tuberculin test reactivity
> /= 5mm of induration : HIV, immunosupressive therapy, recent TB contact.
> /= 10mm immigrants from high prevelance countries, injection drug users. Children younger than 4 years old, AIDS patient
> /= 15mm : low risk of TB
Specimen
Sputum
Broncho alveolar lavage, pleural fluid, csf, urine, stool, aspiration, blood for haematogenoud TB
