Mycobacteria 1p5k2x

MYCOBACTERIA CORYNEBACTERIA Lecture 40

Faculty: Dr. Alvin Fox 1

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 5

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 10

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 18

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 22 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 28

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) 34

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 40

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 43

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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