Transcript Mycobacterium ---

Mycobacterium
MYCOBACTERIUM
THIS GENUS IS COMPOSED OF:
Strictly aerobic, acid-fast rods, does not
Stain well (gram stain indeterminant),
DNA has high g+c content, unique cell wall,
Mycolic acid carbon chain length > c60
Relatively slow growth (two groups)
A. RAPID GROWERS (Visible colonies in <5 days)
B. SLOW GROWERS (Visible colonies in > 5 days)
TYPE SPECIES: Mycobacterium tuberculosis
THE GENUS MYCOBACTERIUM CAN BE DIVIDED
INTO FOUR BROAD GROUPS
1. THE TUBERCULOSIS COMPLEX
2. SLOW GROWING MYCOBACTERIA
OTHER THAN TUBERCULOSIS (MOTT)
3. RAPIDLY GROWING MYCOBACTERIA
4. MYCOBACTERIUM LEPRAE
Acid Fastness Stain
(Ziehl-Neelsen stain)
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flood the slide with basic
fuchsin (a red dye) in 5%
phenol as a mordant.
heat gently for few minutes to
melt the wax.
wash with 3% HCl in ethanol.
counter-stain with methylene
blue.
Mycobacterium stains red and other
bacteria and the background are blue.
The mycolic acid and its derivatives
are responsible for the acid f
THE TUBERCULOSIS COMPLEX
(Organisms that resemble M. tuberculosis;
Causing a similar type of disease in humans)
1. M. tuberculosis
2. M. bovis
Mycobacterium tuberculosis
M. tuberculosis
General Features
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It is a causative agent for human
tuberculosis.
It grows very slow with a
generation time of 12-15 hours.
On solid media the colonies are
raised and rough with a wrinkled
surface.
M. tuberculosis cells grow either
as discrete rods or as aggregates.
Virulent strains tend to grow as
an aggregated long arrangement
called serpentine cord. Cord
factor is a derivative of mycolic
acids, trehalose 6'-dimycolate.
Transmission
Through respiratory tract, alimentary
tract, injured skin。
TB in the lungs or throat can be infectious.
This means that the bacteria can be spread
to other people. TB in other parts of the
body, such as the kidney or spine, is usually
not infectious.
Who is at risk:
Primary infection: children
Secondary infection: age>25
Virulence factors
No spore, no flagellum, no exotoxin,no
endotoxin, no invasive enzyme
Capsule:polysaccharide;CR3;enzyme;
protect
Lipid/Lipo arabinomannan
Heat-shock protein/Tuberculin protein:
antigenicity, old tuberculin; associate
with wax D can cause hypersensitivity
and form tubercle
Lipid
Lipid: closely related to virulence
a. Phospholipid
monocytes proliferate,cause tubercles
b. Wax D
adjuvent(not only to TB), delayed-type
hypersensitivity
c. Sulfatide硫酸脑苷脂
suppress phagosome combine with lysosome
d. Cord factor (trehalose-6,6-dimycolate)
destroy mitochondria, cause chronic
granulomatosis, suppress WBC wandering
Pathogenesis
primary infection
1) lung infection
secondary infection
2) Out lung infection
Clinical syndromes
a. fatigue, weakness, weight loss and fever
b. pulmonary involvement: chronic
cough,spit blood
c. meningitis or urinary tract involvement
d. bloodstream dissemination: miliary
tuberculosis with lesions in many organs
and a high mortality rate.
Primary Tuberculosis
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The organisms are
transmitted among human via
aerosol.
TB bacilli lodge in the alveoli
or lung alveolar ducts and
most of bacilli are
phagocytosed by alveolar
macrophages.
Macrophages migrate to the
hylar lymph node and
generate T cell-mediated
immune response.
(can be monitored by
tuberculin test)
Tuberculin Skin Test
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Tuberculin is a mixture known as purified
protein derivatives (PPD) from TB bacilli.
 It is a test for delayed type hypersensitivity.
Positive reaction, reddening and thickening
(> 5mm) at the site of injection after 2-3
days, indicates cellular immunity to tubercle
bacilli.
MYCOBACTERIUM TUBERCULOSIS
Can infect (disseminate) and cause disease
in many different body locations such as:
1. Meninges
2. Brain
3. Bone
4. Kidney
5. Essentially any organ (lung primary target)
Steps in the development of tuberculosis
Inhalation of bacteria
Bacteria reach lungs,
enter macrophages
Dead
phagocytes,
necrosis
M. tuberculosis
Bacteria reproduce
in macrophages
Lesion begins to form
(caseous necrosis)
Activated
macrophages
Bacteria cease to
grow; lesion calcifies
Lesion
liquefies
Immune
suppression
Spread to
blood organs
Reactivation
Death
Phagocytes,
T cells, and
B cells
trying to
kill bacteria
Bacteria coughed
up in sputum
Immunity
High rate of infection, but low morbidity.
 Nonspecific immune
AIDS, immunosuppressive agents, endocrine
disease, etc.
Immunity-cellular Immunity
First time: TB invade→proliferate on the spot →invade
local lymph node
Macrophage engulf TB
→TH cell
→IL-1 → TH proliferate →bloodstream
Then TH meet TB again
→MCF →macrophages congregate to focus
→MAF →macrophages become more active
→MIF →macrophages stay at the focus
Then if it is successful granulomatosis forms,prevent TB
diffusing;If it is not successful,macrophage can not kill
TB, patients deteriorate.
Immunity
Cellular immunity
3-6 weeks, T cell VS macrophage
1. CD4+TH : INF-γ→macrophage→epithelioid cell
granulomatosis
2. CD8 +TS : granule dependent, dissolve infected
macrophage,kill TB
3. CD4- CD8 –t(γδ-T):Fas dependent, dissolve
infected macrophage,but not kill TB, cause
caseous focus in the center of granulomatosis;
Acidity and lack of oxygen also make TB die.
Immunity
IV hypersensitivity
Koch phenomenon;
wax D+tuberculin protein;
wax D →macrophage→epithelioid
cell→tubercles→protect TB being
phagocytized
Immunity
Humoral immunity
A lot of Ab comes out, but meaningless
TB active patient: immune complex more
TB stable patient: immune complex less
Diagnosis
The steps to diagnose TB infection and
disease include:
 A medical evaluation that includes
history and risk assessment
 The tuberculin skin test
 A chest x-ray
 A bacteriological examination
Diagnosis
1. Specimen: sputum, pus, CSF, urine, etc.
2. Microscopic examination: Ziehl-Neelsen stain
3. Concentration: 4%NaOH-3%HCL; 6% H2SO4
4. Culture:
solid culture (2-4 weeks 37℃) ;
liquid culture (1-2 weeks)
5. Animal inoculation: guinea pig
6. quick Diagnosis: PCR
Skin test
PPD-C
BCG-PPD
>5mm +
>15mm + +
PPD-C>BCG-PPD infected
Mantoux method
When the Mantoux skin test is performed, a
needle is injected into the upper skin layer of
the patient's arm. The arm is examined 48 to
72 hours after the tuberculin injection in
order to evaluate the reaction on the patient's
skin. Any swelling that can be felt around the
site of the injection, also known as induration,
is measured. The diagnosis of TB infection
depends on the size of the measured
induration and the patient's individual risk
factors.
Prevention
BCG vaccination for new infants
Freeze-drying vaccine
rRNA vaccine
eg:south India Chingleput’s failure of BCG
Find and cure patients
Treatment for Tuberculosis
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Treated with a combination of multiple
drugs for a long period of time: rifampin,
isoniazid (INH), pyrazinamide, ethambutol,
and streptomycin.
 Emergence of multi-drug resistant M.
tuberculosis strains.
Mycobacterium avium and
AIDS
Mycobacteria and AIDS
• M. avium is much less virulent than M. tuberculosis
– does not infect healthy people
– infects AIDS patients
• M. avium infects
– when CD4 count greatly decreased
• M. tuberculosis infection
– infects healthy people
– infects AIDS patients
* earlier stage of disease
* more systemic
Clinical features with AIDS
• systemic disease (versus pulmonary)
– greater in AIDS
• lesions often lepromatous
Antibiotic therapy
• selected primarily for M. tuberculosis
• if M. avium involved other antibiotics included
Mycobacterium aviumintracelluare complex
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causes tb like disease in birds, opportunistic
pathogen in humans. Very prominent cause of
disease in aids patients has been decreased
following haart. Not easily transmitted.
(Runyon group III). Difficult to treat ( drug of
choice is rifabutin)
Mycobacterium leprae
HANSEN’S DISEASE (Leprosy)
caused by M. leprae
Hansen’s disease is a chronic, slowly progressive
 granulomatous disease involving ectodermally
derived
 tissue such as the skin and peripheral nerves. The
disease is usually limited to the cooler parts of the
body such as the skin, nose and upper respiratory
tract. It rarely affects internal organs such as the
brain, liver, spleen, kidneys, and bones.
 It has a specific predilection for peripheral nerves.
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4 forms of Leprosy: Lepromatous
Tuberculoid
Borderline
indeterminate