1. Chapter 20 Mycobacterium

3. Incidence and prevalence
Most prominant killer among infectious disease
One-third of the population worldwide is infected
Every year
3 million people die from tuberculosis
8 to 10 million are newly infected.

5. Main factors account for the resurgence of tuberculosis in the United States
Emergence of multi drug-resistant strains of M. tuberculosis
Immigration of infected persons from countries where TB is prevalent
Prevalence of HIV infection and AIDS
Reactivation of disease in the elderly

6. Content
M.tuberculosis
M. leprae(self study)

7. M. tuberculosis

8. A. Biological properties
Shape and structure
Slender, rod-shaped bacterium, 0.4*1-4μm
Nonmotile,no spore,no capsule
L-form bacteria after anti-tubercle treatment or old age
Lipid: resistant to common stain

9. Ziehl-Neelsen stain (acid-fast stain)
Acid-fast positive---acid fast bacilli
M.TB. smear, stained with carbolfuchsin (5minutes)
decolorized with acid-alcohol
Counter-stained with methylene-blue
Ziehl-Neelsen stain technique is employed for identification of acid fast bacteria

10. A. Biological properties
Cultivation
obligate aerobes,37℃,
slow growth: hrs / 2-4 w
fastidious: Lowenstein-Jensen medium (L-J) ..

11. A. Biological properties
Resistance
dry
acid and alkaline
dyes: e.g., malachite green or crystal velvet
Sensitivity
moist heat
UV radiation
alcohol

12. A. Biological properties
Variation
Morphology, colony appearance,
virulence ,drug resistance
BCG(Bacilli Calmette-Guerin):
Made by Calmette and Guerin; since 1908
attenuated stain of mycobacteria bovis and is an effective immunization against tuberculosis

13. B. Pathogenicity – Virulence factor
neither endotoxin or exotoxin nor invasive enzyme
intracellular pathogen
Lipids
Protein
-- induces hypersensitivity of the host
-- Tuberculin test
Polysaccharides

14. B. Pathogenicity high content lipid Slow growth Fastidious
Acid-fast stain
Slow growth
Fastidious
A virulence factor
Lipid: resistant to common stain

15. Lipid wax-D Phospholipids Cord factor ---delayed hypersensitivity
---immune adjuvant
Phospholipids
---proliferation of mononuclear cells, and induce caseous necrosis and tuberculoma
Cord factor
“serpentine cords”
inhibits migration of leukocytes, chronic granuloma,destroy mitochondria membranme

16. Sulfatide
inhibit the fusion of lysosome and phagosome

17. B. Pathogenicity – Disease
Pathogens
M. tuberculosis-- only human host
M. bovis-- human and cattle
Tuberculosis is chronic infectious disease that can involve any site of body
Lung infection is most common

18. Transmission respiratory route (main) gastrointestinal route
impaired skin

19. B. Pathogenicity – Disease
Lung infection (pulmonary tuberculosis )
Primary tuberculosis
Post-primary (secondary) tuberculosis
Extrapulmonary tuberculosis
kidney,brain,bone,joints,etc.

20. B. Pathogenicity – Disease-- Pulmonary tuberculosis
Primary tuberculosis
Infected for the first time
In young children
Ghon complex (or primary complex)
--combination of a single lesion in lung and caseation in regional lymph nodes in the lung’s hilum
Clinical type: usually mild and asymptomatic
Result in calcification and fibrosis

21. primary complex

22. B. Pathogenicity – Disease-- Pulmonary tuberculosis
Post-primary (secondary) tuberculosis
in the elderly or immunosuppressed individuals who have had primary infection
the reactivation of the bacilli that survived in the primary tuberculosis
the inhalation of new bacilli from the environment
clinical type: localized and severe
Caseation and cavity forming --- open case

23. Miliary tuberculosis

24. Caseous tuberculosis

25. C. Immunity Intracellular pathogen Immunological reaction
Cell-mediated immunity (4～6 weeks after infection)
Humoral immunity: circulating Abs → no defensive roles
Infection immunity: The immunity to the bacilli depends on the existence of organisms.
Cell-mediated immunity & hypersensitivity
develop at the same time mediated by T cells
caused by different components of bacilli
rRNA →immnue response
protein antigens (tuberculin along with wax D) → hypersensitivity

26. Tuberculin test
Definition
a skin test to determine the presence of the immunity and hypersensitivity of the host to M. tuberculosis based on positive reaction of subject to tuberculin

27. Tuberculin test Materials Methods
old tuberculin (OT): heat-killed, filtered proteins of M. Tuberculosis
purified protein derivative (PPD)
Methods
intradermal infection of tuberculin
read in hrs
Measure induration

28. Tuberculin test Results and interpretation
induration ≥ 5mm in diameter
---Positive
---Previous infection but not necessarily active disease
---after BCG vaccination
induration ≥ 15mm in diameter
---intensive positive
---active disease
induration <5mm
--- a negative reaction
--- not contact with M. tuberculosis before
---false reaction
Exclude these possibilitys.
early stage of infections
the elderly
patients with severe tuberculosis and other infectious disease (AIDS)
the use of immunosuppressive drugs

29. D. Laboratory diagnosis
Decontamination and concentration of specimens
Treated with NaOH (sodium hydroxide) to kill other contaminating bacteria
Concentrated by centrifugation
Smears— acid-fast stain
Culture
Use to confirm diagnosis of TB
DNA detection, serology and antigen detection
PCR (polymerase chain reaction)
ELISA

30. E. Prevention and Treatment
BCG
Recommended in immunization programs or TB control programs in China
New born infants and persons who have negative tuberculin test
Immnue sustaining period : 3-5 years
6-8 weeks later, tuberculin test will become positive

31. E. Prevention and Treatment
multiple drugs
usually lasts from 6-9 months
first-line drugs: rifampin、isoniazid、streptomycin、pyrazinamide
second-line drugs: kanamycin, cycloserine, viomycin