Mycobacterium

Filename: Myco.ppt

Outline

• Microbial characteristics

• Diseases
  • Tuberculosis
  • Leprosy

• Treatment

• Prevention

Mycobacterium

• Mycobacteriaceae are represented by the single genus Mycobacterium

• Closely related to the genera Corynebacterium and Nocardia. Rhodococcus
  • previously called the CNM group

CELLULAR Morphology

• Strongly acid fast weakly Gram positive

• Form rods with occasionally branched filaments and no aerial mycelium.
  • Non motile, no spores, no capsule

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COLONIAL Morphology

• Solid surface
  • The time for visible colonies 2-40 days
• Diffusable pigments are rare

Saprophytic Mycobacteria

• Grow at 22 C

• Grow rapidly

• Produce pigment

• weakly acid fast

Easily confused with pathogens

Growth Parameters Mycobacterium

• PHYSIOLOGICAL
  • aerobes
  • resistant to penicillin
  • divided into two groups
    • generally grow slowly
    • some grow fast
  • high lipid content in both the cell and the cell wall

Growth Media

• Simple synthetic media *

• Complex Organic media **

• Oleic acid Albumin ***

Simple synthetic media

• growth poor
  • large inocula
  • slow

• toxic fatty acids inhibit growth
  • Fatty acids neutralized by serum or albumin
  • activated charcoal helps

Oleic Acid Albumin Medium

• Hydrophobic cell wall
  • Mycobacteria grow in clumps

• Tweens wet surface of cells
  • Disperse clumps
  • Encourage more rapid growth

Mycobacterial Cell Wall

• “Cord Factor”
  • virulence

• Protein Fraction
  • tuberculin test

• Lipids
  • Acid fast
  • symptoms

• Polysaccharides
  • immunity?

Cord factor

• Serpentine cords

• found in cell wall

• mycolic acid
  • trehalose- 6,6’ dimycolate

• inhibits leucocytes

• chronic granulomas

Cell Wall

Adjuvanticity

• Muramyl dipeptide

• subunit of peptidoglycan

• Stimulates immune response non-specifically

Protein fractions

• In cell wall

• bound to waxes

• tuberculin sensitivity !!!

• induce antibodies???

Mycobacterial Lipids

• Cell wall rich in lipids

• Responsible for acid fast reaction

• Induce adverse cellular immunity

• Caseation necrosis

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Tuberculin Test: Method

• Injected subdermally with protein extract
  • OT Old tuberculin
  • PPD Purified Protein Derivative

Tuberculin Reaction

• develops 24-48 hours

• read after 48-72 hours

• edema, erythema

• necrosis

• ᡂ mm

Tuberculin Test:Interpretation

• Positive
  • infected with tuberculosis in past
  • risk of developing the disease
  • confirm with X rays
  • antibiotic therapy

• Negative
  • never infected
  • high risk occupations
  • immunize?

Mycobacterium:Diseases

• Chronic long term diseases

• Tuberculosis
  • Mycobacterium tuberculosis
  • Koch 1982
  • Other mycobacteria produce similar disease
    • M. bovis, M. avium, M kansasii, M. intracellular

• Leprosy
  • Mycobacterium leprae
  • Hansen 1873

Other Mycobacterial Diseases

• Skin infections
  • Mycobacterium tuberculosis
  • Mycobacterium marinum
  • Mycobacterium ulcerans

• Lymph glands
  • Mycobacterium scrofulaceum
  • Mycobacterium tuberculosis

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Tuberculosis

Localized Infection

• Entry
  • Respiratory

• Disease
  • Pneumonia
  • granulomatous lesions

• Exit
  • respiratory

Systemic Infection

• Entry
  • respiratory

• Spread
  • Lymphatic & hematogenous

• Disease
  • granulomas any site

• Exit
  • respiratory

Tuberculosis

• Two types
  • Primary -Exudative tuberculosis
  • Reactivation-Productive tuberculosis

• Initial sites
  • lungs, gastrointestinal tract

• Spread through lymphatics to lymph nodes
  • intracellular!!!
  • later spread through blood stream

• Secondary sites
  • ALL organs except muscle

Radiologic Differences between primary and post primary tuberculosis

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X-Ray primary TB

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Exudative tuberculosis

• Acute inflammatory reaction
  • Tuberculin positive

• Frequent in lungs
  • Pneumonia symptoms
    • edema fluid
    • PMNs around the bacteria
    • Later monocytes

• Outcomes
  • heal
  • tissue necrosis
  • Productive TB

Productive Tuberculosis

• Secondary spread

• Chronic granuloma
  • Centre multinucleated giant cells
  • Midzone of epitheloid cells
  • Periphery- fibroblasts monocytes

• Tubercle
  • granuloma becomes fibrous
  • caseation necrosis
  • calcification

Treatment

• Antituberculosis drugs
  • Isoniazid
  • Ethambutol
  • Rifampin
  • Streptomycin

• Multiple drug resistant strains

• Thus drugs used concomitantly
  • Strept + INH; INH + ethambutol; ethamubutol +rifampin etc

Prevention & Control

• Public health measures
  • Tuberculin X rays

• Eradicate bovine tuberculosis
  • slaughter
  • pasteurization

• treat asymptomatic converters in children

• Immunization
  • BCG - inadequate
  • high risk groups nurses, lab techs, vets

The End

Short Answers

• Construct a table of the virulence factors associated with ??? and the biological activity of each

• Describe the clinical manifestations of ???

• Construct a table listing the common ??? species and the associated human diseases.