Mycobaterium tuberculosis

1. M. Tuberculosis
M. tuberculosis
A.L. Samer Faisal

2. Mycobacterium Tuberculosis
General Characteristics
- Family – Myobacteria
- Aerobic rod-shaped bacilli
- “Acid fast” bacteria
- Lack of spore formation and toxin production
- No capsule, flagellum (non-motile)
- Generation time of 18- 24 hours but requires 3-4
weeks for visual colonies
Pathological Features
- Principle cause of Human Tuberculosis
- Intracellular pathogen (alveolar macrophages)
- Waxy, thick, complex cellular envelope
- Produces tubercles, localized lesions of M.
tuberculosis
SEM of M. tuberculosis
M. Tuberculosis
(stained in purple)

3. Mycobacterial Cellular Envelope
General Features
- Thick, waxy and complex
- Higher fluidity in more external
regions than internal regions
- Relatively impermeable to
hydrophilic solutes
- Contain porins protein (selective
cationic + channels)
Main Components
- Peptidoglycan
 contains N-glycolylmuramic
acid instead of N-acetylmuramic
acid
- Arabinogalactan
(arabinose+galactose)
- Mycolic Acids (60% of cellular
envelope)
- Lipoarabinomannan (LAM)
glycolipid (virulence factor)

4. Cont.
The presence of mycolic acids gives M. tuberculosis many characteristics
that defy medical treatment. They lend the organism increased resistance
to chemical damage and dehydration, and prevent the effective activity
of hydrophobic antibiotics. In addition, the mycolic acids allow the
bacterium to grow readily inside macrophages, effectively hiding it from
the host's immune system. Mycolate biosynthesis is crucial for survival
and pathogenesis of M. tuberculosis. It’s confirm their acid-fast
characteristics

5. Chest X-ray of a person with advanced tuberculosis. Infection
in both lungs is marked by white arrow-heads
(Caseous necrosis), and the formation of a cavity is marked by
black arrows.

6. Lab diagnosis
Specimen:
• Sputum, chest x-ray and surgical biopsy.
• CSF- if tubercuosis meningitis is suspected
Microscopy:
• Acid fast rods
• Non-motile
• Non sporing
• Obligate aerobe
• Non capsulated
• Ziehl-neelson staining is used
Culture:
Grow slowly with doubling time of 18 hours. (the amount of time
it takes for a cell to divide) (such as a tumor) to double in size.
Lowenstenin Jensen agar
Raised, dry, cream colored colonies are visible after 2 to 3 weeks and sample is not discarded until 6 weeks of incubation.
Nucleic acid amplification test (PCR)

7. Diagnosis of TB
? ?

8. CSF sample - if tubercuosis
meningitis is suspected
1- Acid-fast staining
of sputum samples

9. Diagnosis of TB
2- TB skin test - injection of M. tuberculosis
proteins (tuberculin)
- positive test leads to red area at injection
site

10. 3- PCR polymerase chain
amplification
1) Diagnose tuberculosis rapidly by identifying DNA from M.
tuberculosis in clinical samples.
2) Determine rapidly whether acid-fast organisms identified by
microscopic examination in clinical specimens are
M.tuberculosis
3) Identify the presence of genetic modifications known to be
associated with resistance to some anti mycobacterial
agents.
4) Determine whether or not isolates of M.tuberculosis from
different patients have a common origin in the context of
epidemiological studies.

12. 4- Direct Microscopy identification
M. tuberculosis is a acid–fast
bacterium, rod-shaped bacterium
measuring 2-4 x 0.2-0.5 μm. They
appear as bright red rods against a
contrasting background.
The Ziehl-Neelsen stain is used to
demonstrate the presence of the bacilli
in a smear. The technique is simple,
inexpensive and detects those cases of
tuberculosis who are infectious.

16. Antibacterial chemotherapy:
- Combination of first and second line drugs for
the first 2 months which could include:
- Isoniazid
- Rifampicin
- Pyrazinamide
- Streptomycin or Ethambutol
- Next 4 months, combination of:
- Isoniazid
- Rifampicin
Treatment
- Early resistance to isoniazid: other first-line drugs
such as ethambutol, streptomycin, pyrazinamide and
fluoroquinolones can be added to drug arsenal
(treatment period also extended).
- These drugs are relatively effective in killing the bacteria,
however, they also produce a wide variety of side effects.

17. First line drugs:
- Bactericidal agents: kill (destroy) active bacteria, important
in the early stages of infection.
Second line drugs:
- Bacteriostatic: hinder (inhibit) bacterial growth.
- Strengthen treatment in the case of resistant bacteria.
- Less efficient and generally more toxic than first line
drugs.
Inappropriate chemotherapy:
- Monotherapy (single drug treatment)
- Decreased treatment period
- Low absorption of drugs
Treatment

18. Drug Bactericidal or
Bacteriostatic
Mechanism of Action Mutation
Rate
Side Effects
Isoniazid Bactericidal to
rapidly dividing
bacteria and
bacteriostatic
to slowly
dividing
bacteria
Pro-drug: activated by a
bacterial catalase.
Inhibits enoyl-ACP
reductase (key enzyme in
fatty acid synthesis, different
than equivalent mammalian
enzymes)
1 in 105
- 106
Rash, abnormal liver function,
anemia, peripheral
neuropathy, mild CNS effects
Rifampicin Bactericidal Inhibits transcription by RNA
polymerase
1 in 108
Fever, immune reactions, GI
irritation, liver damage, can
cause tears and urine to turn
red/orange
Streptomycin Bactericidal Inhibits initiation of protein
synthesis
1 in 108
- 109
Damage to the ears, nausea,
rash, vomiting, vertigo
Ethambutol Bacteriostatic Prevents formation of the
cell wall
1 in 107
Decrease in visual acuity,
colourblindness and other
visual defects, joint pain,
nausea, vomiting, fever,
malaise, headache, dizziness
Fluoroquinolones Bactericidal Act manly on DNA gyrase
(DNA gyrase: introduces
negative supercoils into
DNA)
Tendon damage, heart
problems, swelling of face and
throat, shortness of breath,
rash, loss of consciouness
Pyrazinamide Bacteriostatic,
Bactericidal
Accumuates causing
cellular damage
Joint pain, nauseau, vomiting,
rash, malaise, fever,
photosentivity
Treatment

19. •Q. What is the purposeQ. What is the purpose
of using cocktail ofof using cocktail of
drugs for TB treatment?drugs for TB treatment?

20. • Ans. to ensure
resistant strains do
not arise

21. - M. tuberculosis: naturally resistant to
certain antibiotics due to presence of:
- Drug-modifying enzymes
- Drug-efflux systems
- Hydrophobic cell wall
- Mycobacteria undergo natural
mutations which can lead to
development of drug resistance.
- TB is treated by administration of
combination chemotherapy:
decreases probability of
development of drug resistance.
- Development of increasingly resistant
strains mainly due to: Patient non-
compliance
Drug Resistance and Tuberculosis

22. Prevention
• Bacille Calmette-Guerin (BCG) Vaccine is
available, and is used for tuberculin-
negative individuals under sustained
heavy risk of infection.
• Isoniazid is used prophylactically, e.g.
for tuberculin positive, asymptomatic
individuals, who need
immunosuppressive therapy
for other illnesses

23. THANKTHANK
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