Mycobacterium, Chlamydiae

							Mycobacterium, Chlamydiae,
       Rickettsiae

     20 Rabiulawal 1430H/
         17 Mac 2009
                Mycobacteria
   Rod-shaped, aerobic bacteria, non-sporing, slow
    growth rate than most bacteria.
   They do not readily stain, but capable of
    resisting decolourisation by acid or alcohol,
    hence “acid-fast” bacilli.
   Acid-fastness depends on the waxy envelope.
   Ziehl-Neelsen technique.
   Mycobacterium tuberculosis, Mycobacterium
    leprae, Mycobacterium avium-intracellulare.
   An acid fast stain is used to diagnose the presence of
    mycobacteria in tissue and cytologic preparations. Note
    the thin red rod-like organisms.
                Identification
   Culture: selective and non-selective medium.
   A) Semisynthetic agar media - contain albumin,
    neutralises the toxic and inhibitory effects of
    fatty acids in the specimen. Use to observe
    colony morphology.
   B) Inspissated egg media – plus Malachite green
    to inhibit other bacteria.
   C) Broth media – small inocula, adding Tweens
    wet the media surface and permit dispersed
    growth of Mycobacterium.
   Grow in clumps or masses because of the
    hydrophobic character of the cell surface.
         Growth of Mycobacterium




   Hydrophobic cell surface causes them to clump and
    inhibits permeability of nutrients into the cell.
                Tubercle bacilli
   Tubercle bacilli are resistant to drying and
    survive for long periods in dried sputum.
   Mycobacterial cell walls can induce delayed
    hypersensitivity and some resistance to infection
    and can replace whole mycobacterial cells in
    Freund’s adjuvant.
   A) Cell walls – rich in lipids, which largely bound
    to proteins and polysaccharides. Attribute for
    granuloma formation, caseous necrosis and
    acid-fastness.
   On closer inspection, caseous necrotic tissue is seen to
    constitute the granulomas in this gross appearance of a
    Ghon complex. Most patients with primary tuberculosis
    are asymptomatic, and the granulomas resolve.
              Tubercle bacilli

   B) Proteins – when proteins bound to a
    wax fraction, they elicit the tuberculin
    reaction (sensitivity); can stimulate
    antibodies production.
   C) Polysaccharides – role are uncertain.
       Pathogenesis & Pathology
   Proliferation of virulent organisms + interaction
    with the host = disease
   2 host responses:
   1) delayed-type hypersensitivity reaction to
    mycobacterial proteins.
   2) Cell-mediated immunity (CMI) activates
    macrophages to destroy mycobacteria-contained
    within their cytoplasm.
   Tubercle bacilli spread by lymphatic channels
    and bloodstream.
   Mycobacteria reside intracellularly in monocytes,
    reticuloendothelial cells, and giant cells.
Primary Infection & Reactivation
   When a host has first contact with
    tubercle bacilli, acute exudative lesions
    develop. The lymph nodes undergoes
    massive caseation, which usually calcifies.
   Reactivation is usually caused by tubercle
    bacilli that have survived in the primary
    lesion. Characterised by chronic tissue
    lesions, formation of tubercles, caseation
    and fibrosis.
   The caseous
    necrosis is
    extensive, and
    cavitation is
    prominent. Such
    patients can be
    highly infectious.
   Extensive cavitation of
    multiple granulomas
    of lung are typical for
    secondary tuberculosis
    from reactivation of
    primary infection or
    reinfection as an
    adult. Such lesions
    have a predilection for
    appearance in the
    upper lobes of the
    lung.
               Tuberculin Test
   Material is reactive tuberculoproteins.
   Dose of tuberculin – a large amount injected
    intracutaneously into a hypersensitive host may
    give rise to severe local reactions and a flare-up
    of inflammation and necrosis at the main sites of
    infection, normally 5 TU (TU=tuberculin units).
   Reactions – had primary infection with tubercle
    bacilli develops induration.
     Diagnostic Laboratory Tests
   1) Specimens
   2) Decontamination and concentration of specimens –
    liquefy with N-acetyl-L-cysteine, decontaminate with
    NaOH.
   3) Smears - __________, __________tested for acid-
    fast bacilli by ________________; fluorescence
    microscopy with auramine-rhodamine stain.
   4) Culture : selective/non-selective; anticoagulated
    blood for M. avium complex; growth rate;
    pigmentation in the dark.
   5) DNA detection, serology, and antigen detection.
                 Treatment

   Chemotherapy.
   Tubercle bacilli prone to spontaneous
    mutants resistant to first-line
    antituberculosis drugs.
   Rx: Isoniazid and rifampin.
   Drug resistance to M tuberculosis is a
    worldwide problem.
               Epidemiology

   Source: human who excretes large
    number of tubercle bacilli, particularly
    from resp T; and close contact.
   The development of clinical disease after
    infection may have a genetic component;
    age; undernutrition and by immunologic
    status; coexisting diseases (silicosis,
    diabetes, AIDS or HIV-infected patients).
           Prevention & Control
   1) Prompt treatment, follow-up with tuberculin
    tests, x-rays.
   2) Drug treatment for asymptomatic tuberculin
    + persons.
   3) Reduced individual host resistance by
    starvation, gastrectomy, HIV-infected.
   4) Immunisation : BCG (bacillus Calmette-
    Guèrin, a live attenuated bovine
    organism@tubercle bacilli).
   5) The eradication of tuberculosis in cattle and
    the pasteurisation of milk have greatly reduced
    M. bovis infections.
           Other Mycobacteria
   Tubercle bacilli include M. tuberculosis, M.
    bovis.
   M. avium complex commonly cause
    opportunistic infection ni AIDS.
   M. kansaii is a photochromogen, can
    produce pulmonary and systemic disease
    identical to tuberculosis, esp in patients
    with impaired immune response.
         Mycobacterium Leprae
   Causes leprosy.
   Are regularly found in skin scrapings or mucous
    membranes (nasal septum) in lepromatous
    leprosy.
   Disease is divided into 2 types: lepromatous and
    tuberculoid.
   Systemic manifestations of anemia and
    lymphadenopathy may also occur. Amyloidosis
    may develop.
       Treatment and Prevention
   First-line therapy is sulfones for both tuberculoid
    and lepromatous leprosy.
   Leprosy is most likely to occur when small
    children are exposed for prolonged periods to
    heavy shedders for bacilli. Incubation period is
    probably 2-10 years.
   Prevention is by identification and treatment of
    patients with leprosy, given chemoprophylactic
    drugs until the treatment has made them
    noninfectious.
                Chlamydiae

   3 species that infect human
   Obligate intracellular parasites
   All members of Chlamydiae exhibit similar
    morphologic features, share common
    group antigen, and multiply in cytoplasm
    by distinctive developmental cycle.
Cell pathology:

1. Elementary body
   EB
2. Reticulate body RB
   (larger, devoid of
   electron-dense
   nucleoid)
3. Cytoplasmic
   inclusion
                   Rickettsiae
   Obligate intracellular parasites, are transmitted
    to humans by anthropods.
   Staining: Giemsa, Gimenez, acridine orange.
   Characterised by fever, headache, malaise,
    prostration, skin rash and enlargement of spleen
    and liver. These are the features of typhus
    fever.
   Spotted fever and Q fever (resembles influenza,
    hepatitis, nonbacterial pneumonia).
   Rx: tetracyclines, chloramphenicol.