Chapter 20 Mycobacterium

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.

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

Content M.tuberculosis M. leprae(self study)

M. tuberculosis

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

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

A. Biological properties Cultivation obligate aerobes,37℃,6.5-6.8 slow growth: 18-24 hrs / 2-4 w fastidious: Lowenstein-Jensen medium (L-J) ..

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

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

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

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

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

Sulfatide inhibit the fusion of lysosome and phagosome

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

Transmission respiratory route (main) gastrointestinal route impaired skin

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

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

primary complex

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

Miliary tuberculosis

Caseous tuberculosis

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

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

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 48-72 hrs Measure induration

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

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

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

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