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Flashcards in Micro TB Deck (38):
1

Species of
Mycobacteria :

❖ Mycobacterium tuberculosis complex
cause tuberculosis.
❖ Mycobacterium leprae causes
leprosy.
❖ Atypical Mycobacteria /
Mycobacteria other than
tuberculosis ( MOTT) cause
infections in immunosuppressed
patients.

2

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)

3

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.

4

Mycobacterium stains

Ziehl-Neelsen ( Z-N ) and
Auramine staining

5

Pathogenesis of Tuberculosis : 1

Mycobacteria acquired
by airborne droplet
reaches the alveolar
macrophages

6

Pathogenesis of Tuberculosis : 2

This starts cell mediated
immune response; which
controls the
multiplication of the
organism but does not
kill it.

7

Pathogenesis of Tuberculosis : 3

Granuloma is formed,
organism lives in
dormant state (latent
tuberculosis infection).

8

Pathogenesis of Tuberculosis : 4

Patient show evidence of
delayed cell mediated
immunity ( CMI ).

9

Pathogenesis of Tuberculosis : 5

Disease results due to
destructive effect of CMI.

10

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):

11

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

12

Secondary TB Clinically: signs

fever, cough,
hemoptysis ,weight loss &
weakness.

13

Source of secondary TB

Endogenous (reactivation of an
old TB)
Exogenous (reinfection with
new strain)

14

Immunity to Tuberculosis

Cell-mediated immunity associated with delayed hypersensitivity reaction

15

Immunity to Tuberculosis detection and duration ?

Detected by tuberculin skin test
2-10 weeks

16

Tuberculin Skin Test NEGATIVE


➢ No previous infection
➢ Pre-hypersensitivity
stage
➢ Lost TB sensitivity
with loss of antigen

17

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

18

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

19

Tuberculin Skin Test POSITIVE
3. >15mm
induration
positive in

3. >15mm
induration
positive in:
❖ Any persons
including
those with no
risk of TB

20

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)

21

Laboratory Diagnosis of TB Direct microscopy of
specimen

Z-N or (Auramine ) stain.

22

Laboratory Diagnosis of TB 3) Culture

Culture: the gold standard.
Important for identification and
sensitivity.

23

the gold standard.
Media used:

it contains ?

Media used:
Lowenstein-Jensen media (LJ).

Media contains: eggs,
asparagine, glycerol, pyruvate/
malachite green.*

24

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).

25

Laboratory Diagnosis of TB
Other media plus LJ media may be used:

Fluid media (middle Brook).
Automated methods
Measurement Interferon –gamma release assay (IGARAs)
Molecular method

26

Automated methods

Bactec MGIT ( Mycobacteria Growth Indicator Test ).

27

Measurement Interferon –gamma release assay (IGARAs):

Measurement Interferon –gamma release assay (IGARAs): positive in latent TB

IF-γ) secreted from
sensitized lymphocytes challenged by the same mycobacterial proteins in a patient previously exposed
to disease, will produce interferon gamma. Has a specific significance than tuberculin skin test.
(increased risk of developing TB).

28

Molecular method

1-ProbTech ;detects nucleic acid directly from respiratory samples.
2-Xpert MTB/RIF detect nucleic acid and resistance to rifampicin .
3-PCR(polymerase chain reaction): molecular test directly from
specimen (CSF).

29

Management of a TB case

❖Isolation for 10-14 days ( for smear positive cases i.e. > 1000 organisms / ml of sputum
considered infectious case ).
❖ Triple regimen of therapy. Why? (combination of 3 or 4 drugs)
1. To prevent resistant mutants
2. To cover strains located at different sites of the lung
3. To prevent relapse
❖ Treatment must be guided by sensitivity testing.

30

Treatment of TB
First Line Treatment

❖ Isoniazid (INH)
❖ Rifampicin (RIF)
❖ Ethambutol (E)
❖ Pyrazinamide (P)
❖ Streptomycin (S)
❖ Directly Observed Therapy (DOT).

31

Treatment of TB
First Line Treatment
For the first 2 months →
the next 4-6 months →

For the first 2 months → INH + RIF + P or E +S For
the next 4-6 months → INH + RIF

32

Treatment of TB Second Line Treatment

❖ PASA ( Para-Aminosalicylic acid).
❖ Ethionamide.
❖ Cycloserine.
❖ Kanamycin.
❖ Fluoroquinolones.

33

Prevention of TB

❖ Tuberculin testing of herds.
❖ Slaughter of infected animals.
❖ Pasteurization of milk to prevent bovine TB.
❖ Recognition of new cases.
❖ Prophylaxis with INH of contacts.
❖ Follow up cases.
❖ Immunization with BCG (live attenuated) to all newborns

34

Tb is transmitted by

inhaling Aerosols not droplets

35

waxy substance that prevents the Tb from being stained by gram stain.

Mycolic Acid

36

will increase the risk of Tb Meningitis

Not taking the BCG vaccine

37

can be given as an anaphylactic

INH

38

Which test can be used to predict the future of Tb?

Quantiferon because it’s specific