1 Mycobacterium. 2 3 Incidence and prevalence One-third of the population worldwide is infected...
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Mycobacterium
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Incidence and prevalence
• One-third of the population worldwide is infected • Every year
– 1.5 million people die from tuberculosis – 8 to 10 million are newly infected.
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Main factors account for the resurgence of
tuberculosis in the United States
• Emergence of multidrug-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
• Socioeconomic decline in urban areas
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Classification
Organisms Growth rate Typical speciesM. tuberculosis complex
slow M. tuberculosisM. bovis
M. leprae No growth on artificial media
Nontuberculosis mycobacteria
Group Ⅰ Slow M. Kansas 堪萨斯分枝杆菌M. Marinum 海分枝杆菌
Group Ⅱ Slow M. Scrofulaceum瘰疬分枝杆菌
Group Ⅲ Slow M. avium-intracellulare鸟-胞内分枝杆菌
Group Ⅳ Rapid(<7d) M. Fortuitum偶发分支杆菌
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M. tuberculosis
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Biological properties• Shape and structure
– Slender, rod-shaped bacterium, nonmotile
– Compositions
• peptidoglycan
• arabinogalactan layer
• high content lipid
– Mycolic acids
– Cord Factor
– Wax
• polypeptide
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free lipids
(wax,cord factor)
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Biological properties
• high content lipid • Mycolic acids • Cord Factor • Wax
Acid-fast stain Slow growth Fastidious A virulence factor
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Ziehl-Neelsen stain (acid-fast stain)
Acid-fast positive
• M.TB. smear, stained with car
bolfuchsin (15minutes)
• decolorized with acid-alcohol
• counterstained with methylen
e-blue
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Biological properties
• Cultivationobligate aerobesslow growth: 18-24 hrs / 2-4 wfastidious: Lowenstein-Jensen medium (L-J)
..
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Biological properties
• Sensitivitymoist heatUV radiationalcohol
• Resistancedryacid and alkalinedyes: e.g., malachite green
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Pathogenicity neither endotoxin or exotoxin nor invasive enzyme
intracellular pathogen
• Lipids• Protein
-- induces hypersensitivity of the host
Tuberculin test
• Polysaccharides• Mycobactin
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Lipid
• Phospholipids ---proliferation of mononuclear cells, cause tu
bercles
• Cord factor ---destroy mitochondria, suppress WBC wande
ring , cause chronic granulomatosis
• Wax D ---adjuvent, delayed-type hypersensitivity
• Sulfatide 硫酸脑苷脂 suppress phagosome combine with lysosome
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Pathogenicity
• PathogensM. tuberculosis-- only human host
M. bovis-- human and cattle
• Transmission– respiratory route (main)– gastrointestinal route– impaired skin
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• Lung infection (pulmonary tuberculosis )
– Primary tuberculosis
– Post-primary (secondary) tuberculosis
• Extrapulmonary tuberculosis
Pathogenicity
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• 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
Pulmonary tuberculosis
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• Post-primary (secondary) tuberc
ulosis – in the elderly or immunosuppresse
d individuals who have had primary
infection
• the reactivation of the bacilli that
survived in the primary tubercul
osis
• the inhalation of new bacilli from
the environment
– clinical type: localized and severe
Pulmonary tuberculosis
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Immunity
• Intracellular pathogen
• Immunological reaction– Cell-mediated immunity (3~ 6 weeks after infecti
on)– Humoral immunity: circulating Abs → no defensiv
e roles– Infection immunity: The immunity to the bacilli de
pends on the existence of organisms.
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Immunity
• Cell-mediated immunity & hypersensitivity– develop at the same time mediated by T cells– caused by different components of bacilli– protein antigens (tuberculin along with wax D)
→ hypersensitivity
• Tuberculin test
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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
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• Materials– old tuberculin (OT): heat-killed, filte
red proteins of M. Tuberculosis
– purified protein derivative (PPD)
• Methods– intradermal infection of tuberculin
– read in 48-72 hrs
– Measure induration
Tuberculin test
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• 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
Tuberculin test
• early stage of infections• the elderly• patients with severe tuberculosis and other infectious disease (AIDS)• the use of immunosuppressive drugs
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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)
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Prevention and Treatment
• Prevention
– BCG, bacillus Calmette-Guerin
• Made by Calmette and Guerin; since 1908
• heat-killed, filtered proteins of M. Tuberculo
sis
• Recommended in immunization programs o
r TB control programs in China
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• Treatment – multiple drugs
– usually lasts for 6-9 months
– rifampin、 isoniazid、 streptomycin、 prazinami
de
Prevention and Treatment
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Nontuberculosis mycobacteria
Organisms Growth rate
Pigment formation in:
Typical speciesLight Dark Group Ⅰphotochromogens
Slow + - M. Kansas 堪萨斯分枝杆菌M. Marinum 海分枝杆菌
Group Ⅱscotochromogens
Slow + + M. Scrofulaceum瘰疬分枝杆菌
Group ⅢNonchromogens
Slow - - M. avium-intracellulare鸟-胞内分枝杆菌
Group ⅣRapid growers
Rapid(<7d) M. Fortuitum偶发分支杆菌
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Characteristics of nontuberculosis mycobacteria
• much less virulent than M. tuberculosis
• opportunistic pathogen in humans
• combined infection with M.tuberculosis, mostly Mycobacterium avium-intracelluare complex.
very prominent cause of disease in AIDS patients.
• difficult to treat
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Mycobacterium leprae
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Biological properties
• Intracellular parasites• Not grow on artificial media and cell culture• Grow in footpads of mice • Optimal temperature: 30℃
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4 forms of Leprosy
• Lepromatous
• Tuberculoid
• Borderline
• indeterminate
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Pathogenesis• Transmission
Respiratory tract
Direct contact
• Disease-- leprosy (Hansen's Disease)
– Lepromatous type
– Tuberculoid type
– Infect skin, nerves
– Chronic disease
– Disfigurement
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Lepromatous type Tuberculoid type
CMI deficient normal
lepromin negative positive
skin lesion abundant acid-fast bacilli
few bacilli
course progressive and malign
benign and nonprogressive
infectivity high low