Micro TB Flashcards
Species of
Mycobacteria :
❖ Mycobacterium tuberculosis complex cause tuberculosis. ❖ Mycobacterium leprae causes leprosy. ❖ Atypical Mycobacteria / Mycobacteria other than tuberculosis ( MOTT) cause infections in immunosuppressed patients.
Mycobacterium
tuberculosis complex
1- M. tuberculosis (human type) very common
2- M. bovis (bovine type) (rare because of
pasteurization of milk)
3- M. Africanum
4- BCG strains (used for vaccination but in rare
cases it can cause TB in immunocompromised children)
Characteristics of the Genus Mycobacteria
Slim, rod shaped, non-motile, do not form spores
Do not stain by Gram stain because it Contain high
lipid conc. ( Mycolic acid ) in the cell wall which
resist staining.
Mycobacterium stains
Ziehl-Neelsen ( Z-N ) and
Auramine staining
Pathogenesis of Tuberculosis : 1
Mycobacteria acquired
by airborne droplet
reaches the alveolar
macrophages
Pathogenesis of Tuberculosis : 2
This starts cell mediated immune response; which controls the multiplication of the organism but does not kill it.
Pathogenesis of Tuberculosis : 3
Granuloma is formed,
organism lives in
dormant state (latent
tuberculosis infection).
Pathogenesis of Tuberculosis : 4
Patient show evidence of
delayed cell mediated
immunity ( CMI ).
Pathogenesis of Tuberculosis : 5
Disease results due to
destructive effect of CMI.
Non-pulmonary TB :
TB of lymph nodes (cervical, mesenteric) ● TB meningitis (specifically in children, immunocompromised and old people) ● TB bone & joint ● TB of the genitourinary system. ● TB miliary (Blood and other organs.) ● TB of soft tissue (cold abscess):
TB of soft tissue (cold abscess
lacks inflammation with Caseation (shows no signs of inflammation)
Caseation: due to delayed hypersensitivity reaction. Contains many bacilli ,enzymes, O2,N2 intermediates,
necrotic center of granuloma with cheesy material
Secondary TB Clinically: signs
fever, cough,
hemoptysis ,weight loss &
weakness.
Source of secondary TB
Endogenous (reactivation of an
old TB)
Exogenous (reinfection with
new strain)
Immunity to Tuberculosis
Cell-mediated immunity associated with delayed hypersensitivity reaction
Immunity to Tuberculosis detection and duration ?
Detected by tuberculin skin test
2-10 weeks
Tuberculin Skin Test NEGATIVE
➢ No previous infection ➢ Pre-hypersensitivity stage ➢ Lost TB sensitivity with loss of antigen
Tuberculin Skin Test POSITIVE
1. >5mm induration
positive in:
1. >5mm induration positive in: ❖ Recent contact with active TB ❖ HIV or high risk of HIV ❖ Chest X-ray consistent with healed TB
Tuberculin Skin Test POSITIVE
2. >10mm induration
positive in:
2. >10mm induration positive in: ❖ IV drugs user ❖ HIV seronegative* patient ❖ medical conditions eg: diabetes, malignancy ❖ Residents & employee at high risk, and also patients from country with high incidence ❖ Children < 4 years or exposed to adult high risk group
Tuberculin Skin Test POSITIVE
3. >15mm
induration
positive in
3. >15mm induration positive in: ❖ Any persons including those with no risk of TB
Laboratory Diagnosis of TB
1) Specimens
Pulmonary TB: 3 early morning(1) sputum samples or bronchial lavage(2) or gastric washing(3) (infants) ❖ TB Meningitis: Cerebrospinal fluid ( CSF). ❖ TB of the genitourinary system: 3 early morning urine. ❖ TB bone & joint:Bone, joint aspirate. ❖ TB of lymph nodes: pus or tissues, NOT swab. ❖ Repeat the sample.(4)
Laboratory Diagnosis of TB Direct microscopy of
specimen
Z-N or (Auramine ) stain.
Laboratory Diagnosis of TB 3) Culture
Culture: the gold standard.
Important for identification and
sensitivity.
the gold standard.
Media used:
it contains ?
Media used:
Lowenstein-Jensen media (LJ).
Media contains: eggs,
asparagine, glycerol, pyruvate/
malachite green.*
the gold standard. appearance :
Colonies appear in LJ media after 2-8 weeks as eugenic, raised, buff, adherent growth -enhanced by glycerol: (MTB) -enhanced by pyruvate: (M.bovis).
