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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