MYCOBACTERIA CORYNEBACTERIA Lecture 40

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MYCOBACTERIACORYNEBACTERIALecture 40
Faculty Dr. Alvin Fox
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KEYWORDS

• Acid Fast
• Tuberculosis (TB)
• M. tuberculosis (MDR, XDR)
• M. avium - M. intracellulare complex
• M. bovis
• M. leprae
• Tubercle
• PPD
• Tuberculin
• Mycobactin
• Cord factor
• BCG
• Leprosy (Hansen's Disease)
• AIDS and TB
• Runyon groups
• Mycolic acids

• Diphtheria
• C. diphtheriae
• Loeffler's agar
• Tellurite agar
• Metachromatic bodies
• Diphtheria toxin
• Schick test
• Diphtheroids

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Mycobacterium tuberculosis
obligate aerobe acid-fast rods
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Tuberculosis (TB, consumption)

• M. tuberculosis
• major human disease
• healthy people
• problems
• association with AIDS
• multiple drug-resistance

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• M. avium- M. intracellulare complex (M. avium)

• non-AIDS
• infection almost never
• AIDS
• major bacterial opportunist
• multiple drug-resistance

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M. bovis

• spread from cattle
• infected cattle are culled
• positive skin test
• rarely seen in US

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M. leprae

• leprosy
• major disease of third world
• rare in US

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Transmission -tuberculosis

• M. tuberculosis causes disease
• healthy individuals
• transmitted man-man
• airborne droplets

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Pathogenesis of tuberculosis

• infects lung
• distributed within macrophages
• facultative intracellular pathogen
• inhibits phagosome-lysosome fusion

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Cell-mediated immunity -tuberculosis

• infiltration
• macrophages
• lymphocytes
• granulomas
• tubercules

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Laboratory diagnosis - tuberculosis

• skin testing
• delayed hypersensitivity
• tuberculin
• protein purified derivative, PPD
• X-ray

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Positive skin test -tuberculosis

• indicates exposure to organism
• does not indicate active disease

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• Other minor pathogenesis factors
• tuberculosis

• mycobactin
• siderophore
• cord factor
• damages mitochondria

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Laboratory diagnosis M. tuberculosis

• acid fast bacteria
• sputum

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Laboratory diagnosis M. tuberculosis (culture)

• grows very slowly
• two weeks or longer
• non-pigmented colonies
• niacin production
• differentiates from other mycobacteria

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Tuberculosis

• polymerase chain amplification
• rapid diagnosis

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Antibotic treatment - tuberculosis

• extensive time periods (e.g. 9 months)
• organism grows slowly, or dormant
• two or more antibiotics
• e.g. rifampin and isoniazid
• resistance minimized

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Tuberculosis and Drug resistance

• Multiple drug resistant (MDR)
• resistant to first line drugs
• Extremely drug resistant (XDR)
• Resistant to some of the second line drugs
• Nearly un-treatable

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Vaccination

• BCG vaccine
• an attenuated strain of M. bovis
• not effective
• in US,
• incidence is low
• vaccination not practiced
• immunization interferes with diagnosis

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Mycobacterium leprae
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Leprosy (Hansen's Disease)

• M. leprae
• causative agent
• chronic disease
• disfigurement
• rarely seen in the U.S.
• common in third world
• - effective antibiotic therapy recently
  initiated, incidence way down
• infects the skin
• low temperature

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• ulcers, resorption of bone
• worsened from careless use of hands (nerve damage)

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Leprosy

• tuberculoid
• few organisms
• active cell-mediated immunity
• lepromatous
• many organisms
• immunosuppression

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Production of M. leprae antigens and
pathogenesis studies

• in vitro
• unculturable
• in vivo growth
• low temperature
• armadillo (laboratory and native e.g. TX)
• mouse footpad

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Leprosy

• lepromin
• skin testing
• acid-fast stains
• skin biopsies
• clinical picture

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Other mycobacterial species (including M. avium)

• infect immunocompromised host
• not transmitted man-man, healthy people
• M. avium common
• Other species - rare

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Mycobacterial diseases

• tuberculosis-like
• leprosy-like

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• 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 (helper T cell) count greatly decreased
• M. tuberculosis infection
• infects healthy people
• infects AIDS patients
• earlier stage of disease
• more systemic

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Clinical features with AIDS

• systemic disease (versus pulmonary)
• greater in AIDS
• lesions often lepromatous

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Antibiotic therapy

• selected primarily for M. tuberculosis
• if M. avium involved other antibiotics included

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Other species

• pigmented or not
• pigmentation
• in the light
• in the dark
• growth
• fast
• slow

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Mycobacterial species identification

• cellular fatty acid profiles
• mycolic acid profiles
• genetic markers

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Mycolic acids

• mycobacteria
• longest chain length
• strongly acid fast
• nocardia
• intermediate chain length
• weakly acid fast
• corynebacteria
• shortest chain length
• not acid fast

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Corynebacterium diphtheriae
Gram positive strict aerobe pleomorphic (e.g.
club-shaped)
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Diphtheria

• member of normal flora of pharynx
• overgrowth upper respiratory tract
• pseudomembrane
• chocking
• bacteria do not spread systemically
• The toxin does disseminates
• .

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This child has diphtheria resulting in a thick
gray coating over back of throat. This coating
can eventually expand down through airway and,
if not treated, the child could die from
suffocation CDC
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Diptheria toxin

• spreads
• systemic and fatal injury

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Diphtheria toxin

• B binds to host cell
• A inhibits protein synthesis
• ADP-ribose moiety (NADH) attaches
• elongation factor 2 inhibited

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Treatment

• anti-toxin
• antibiotic

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Immunization against diphtheria (infant)

• disease vanished in US
• without immunization will return
• toxoid ( pertussis and tetanus) DPT
• neutralizing antibodies
• colonization not inhibited
• found in normal flora

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Testing immunity

• Schick skin test
• toxin

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Diphtheria toxin

• coded by bacteriophage tox gene
• not synthesized if iron present
• iron-repressor complex forms
• inhibits expression of tox gene

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Identification - C. diphtheriae

• growth Loeffler's medium
• stain for polyphosphate granules
• metachromatic
• polyphosphate granules (pink) cell (blue)

• tellurite agar
• reduction by bacteria
• tellurium precipitation
• black colonies

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Identification Exotoxin production

• in vivo
• in vitro

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• C. diphtheriae should not be confused with

• diphtheroids
• other corynebacteria
• propionibacteria