MYCOBACTERIA
CORYNEBACTERIA
Lecture 40
Faculty: Dr. Alvin Fox
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KEYWORDS
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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
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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
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worsened from careless use of hands (nerve damage)
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
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