Transcript 16-Mycobacterium-tuberculosis

Batterjee Medical College
Batterjee Medical College
Mycobacterium
tuberculosis
Dr. Manal El Said
Head of Medical Microbiology Department
Batterjee Medical College
Mycobacterium tuberculosis
Diseases
Tuberculosis
Characteristics
• Aerobic & acid-fast rods
• High lipid content of cell wall, which prevents dyes used in
Gram stain from staining organism.
• Lipids include mycolic acids & wax D.
• Grows very slowly, which requires that drugs be present
for long periods (months).
• Produces catalase, which is required to activate isoniazid
to active drug.
Batterjee Medical College
Mycobacterium tuberculosis
Habitat and Transmission
• Habitat is human lungs.
• Transmission is via respiratory droplets produced by
coughing.
Pathogenesis
•Granulomas & caseation mediated by cellular immunity, i.e.,
macrophages
&
CD4-positive
Tcells
(delayed
hypersensitivity).
•Cord factor (trehalose mycolate) virulence factors.
•Immunosuppression
dissemination.
increases
risk
of
reactivation
&
Batterjee Medical College
Mycobacterium tuberculosis
Laboratory Diagnosis
•Acid-fast rods seen with Ziehl-Neelsen stain.
•Slow-growing (3–6 weeks) colony on Löwenstein-Jensen
medium.
•Organisms produce niacin & are catalase-positive.
Rough and buff lowenstein jensen agar
Batterjee Medical College
Mycobacterium tuberculosis
Laboratory Diagnosis
•Acid-fast rods seen with Ziehl-Neelsen stain.
•Slow-growing (3–6 weeks) colony on LöwensteinJensen medium.
•Organisms produce niacin & are catalase-positive.
Skin Test
• PPD skin test is positive if induration measuring 10
mm or more appears 48 hours after inoculation.
• Induration is caused by a delayed hypersensitivity.
• Positive skin test indicates that the person infected
& not that the person has the disease tuberculosis.
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Mycobacterium tuberculosis
Laboratory Diagnosis
Tuberculin skin test (Mantoux test) or PPD test
Batterjee Medical College
Mycobacterium tuberculosis
Treatment
• Long-term therapy (6–9 months) with three drugs, isoniazid,
rifampin, and pyrazinamide.
• A fourth drug, ethambutol, is used in severe cases (e.g.,
meningitis), in immunocompromised patients (e.g., AIDS) &
where the chance of isoniazid-resistant organisms is high
Batterjee Medical College
Mycobacterium tuberculosis
Treatment
• Most patients become noninfectious within 2 weeks of
adequate therapy.
• Treatment of latent (asymptomatic) infections consists of
isoniazid taken for 6 to 9 months.
• Multidrug-resistant (MDR) strains have emerged & require
other drug combinations
Batterjee Medical College
Mycobacterium tuberculosis
Prevention
• BCG vaccine containing live, attenuated Mycobacterium
bovis organisms may prevent or limit extent of disease but
does not prevent infection with M. tuberculosis.
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Atypical Mycobacteria
• These mycobacteria are called atypical because they
differ from M. tuberculosis in various ways.
• Most important difference is that atypical are found in
environment, whereas M. tuberculosis is found only in
humans.
• Atypical are called "Mycobacteria
tuberculosis," or MOTTS.
other
than
M.
• Atypical are subdivided into slow growers & rapid growers
based on whether they form colonies in more than or less
than 7 days.
Batterjee Medical College
Atypical Mycobacteria
The following are important slow growers:
• Mycobacterium avium-intracellulare complex
-They
causes
tuberculosis-like
disease,
especially
in
immunocompromised patients e.g.with AIDS.
- It is highly antibiotic-resistant.
• Mycobacterium kansasii
It causes tuberculosis-like disease but is less antibioticresistant than MAC.
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Atypical Mycobacteria
Mycobacterium marinum :
• It
causes
"swimming
pool
granuloma
or
fish
tank
granuloma," which is a skin lesion at the site of an abrasion
acquired in a swimming pool or an aquarium.
Mycobacterium scrofulaceum
• It causes scrofula, which manifests as swollen, nontender
cervical lymph nodes (cervical adenitis).
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Atypical Mycobacteria
The important rapid grower is:
Mycobacterium fortuitum-chelonei complex
• It causes infections of prosthetic joints and indwelling
catheters.
• It also causes skin and soft tissue infections at the site of
puncture wounds.
• The
organisms
are
antituberculosis drugs.
usually
resistant
to
most
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Mycobacterium leprae
Diseases
Leprosy.
Characteristics
• Aerobic, acid-fast rods.
• Cannot be cultured in vitro.
• Optimal growth at less than body temperature, so lesions
are on cooler parts of the body, such as skin, nose, and
superficial nerves.
Batterjee Medical College
Mycobacterium leprae
Habitat and Transmission
• Humans are reservoir.
• It founds in armadillos, but it is uncertain whether they are
source of infections for humans.
• Mode of transmission is nasal secretions of patients with
lepromatous form.
• Patients with lepromatous form are more likely to transmit
than those with tuberculoid form because they have much
higher numbers of organisms than those with tuberculoid
leprosy.
• Prolonged exposure is usually necessary.
Batterjee Medical College
Mycobacterium leprae
Pathogenesis
• Lesions occur in cooler parts of body, e.g., skin &
peripheral nerves.
• In tuberculoid leprosy, destructive lesions are due to cellmediated response to organism.
• Damage to fingers is due to burns & other trauma, because
nerve damage causes loss of sensation.
• In lepromatous leprosy, cell-mediated response to M. leprae
is lost & large numbers of organisms appear in lesions &
blood.
Batterjee Medical College
Mycobacterium leprae
Laboratory Diagnosis
• Acid-fast rods are abundant in lepromatous leprosy, but few
are found in tuberculoid form.
• Cultures & serologic tests not done.
• Lepromin skin test is positive in tuberculoid but not in
lepromatous form.
Batterjee Medical College
Mycobacterium leprae
Treatment
• Dapsone plus rifampin for the tuberculoid form.
• Clofazimine is added to that regimen for lepromatous form
or if organism is resistant to dapsone.
• Treatment is for at least 2 years.
Batterjee Medical College
Mycobacterium leprae
Prevention
•Dapsone for close family contacts.
•No vaccine is available.