Mycobacteria Flashcards by Daniel Picard

What is the morphology of myocobacteria?

Slender, rod-shaped

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Describe the growth pattern, and staining pattern.

Slow growing

Poor staining and acid fast

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What does acid fast mean?

Once stained, resistant to decolourization by acid

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What is peculiar of the cell wall of mycobacteria?

60% lipid - including long chain fatty acids called mycolic acids

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Why are mycobacteria so tough?

Unique composure makes them resistant to the environment and, they live inside cells

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What are the different mycobacteria classifications?

Tubercle bacilli complex (cause TB)
MOTT - mycobacterium other than tubercle bacilli
Mycobacterium leprae (causal agent of leprosy)

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What bacterium causes leprosy?

Mycobacterium leprae

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What is the mycobacterium from cattle?

Mycobacterium bovis

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What proportion of the world is infected with tuberculosis?

1/3rd

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How does the TB infection become airborne?

IF it aerosolizes - mostly coughing (singing and talking too)

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Why are aerosols so dangerous?

They are carried by air currents and can infect someone very far away

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If the sputum stain returns negative for AFB, what does that mean?

There are not enough bacteria to cause infections - i.e. the person is non-infectious

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What does AFB stand for?

Acid-fast bacillus

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Although the incidence of TB is very low in NA, which groups have higher rates?

Inuit, First Nations, refugees, AIDS and homeless

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What is the hallmark of TB?

A tubercle = caseating granuloma

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Pulmonary TB is ___________ at first, with insidious onset of _______.

asymptomatic

cough

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_______ infectious patients may seem in good health for long periods (TB).

highly

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What symptoms are often seen before the lesion is seen on a chest X-ray?

Hemoptysis, weight loss and fever

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Most pulmonary TB in adults is located where in the lungs?

Apical areas

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How did the TB get to the apical areas of the lungs?

TB spreads via air current - breathed in and goes to lower lung fields.
TB travels through the blood from the primary focus to the apical areas

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What is the only tissue in which we cannot get TB?

enamel

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Describe extrapulmonary TB.

15% of cases
Acquired via hematogenous seeding (blood)
almost non-contagious

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Most people infected with TB do not develop TB, but, how can it be activated?

when the patient becomes immunocompromised

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What are some reasons that latent TB may become active?

organ transplant, chemotherapy or other debilitating disease

rapid, inadvertent weight loss

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What is currently used to determine if somone has been infected by TB?

Mantoux skin test

What is primed to replace the Mantoux skin test?

Interferon gamma release assay

What is the Mantoux skin test (i.e. what is done)?

Intradermal injection of 5 tuberculin units of PPD (purified protein derivative)

What is measured after administration of the 5 tuberculin units of PPD?

Induration (not erythema)

The induration is measured after how much time has expired? Thus, what day is a Mantoux test not administered?

48-72 hours | Not administered on Thursdays

For individuals of high risk for TB (suspicious chest X-ray, contact cases, immunosuppressed), what is a positive result?

Any induration bigger or equal to 5mm

For individuals of moderate risk (i.e. high prevalence countries, healthcare workers, prison or instituations) are positive at what induration size?

bigger or equal to 10 mm

If a person has no risk factors, what is a positive skin test TB result?

induration bigger or equal to 15 mm`

What's a great way to increase measurement precision for TB skin test?

Take ballpoint pen and you will feel where the induration starts.

How can the sensitivity of the TB skin test be increased?

Increased with 2 tests a few weeks apart - two step test

Repeating testing _____ lead to false positives.

doesn't

How long does it take after exposure to develop a positive test result?

4-6 weeks

What is paradoxical about those with advanced TB?

They may become anergic and have a negative test (i.e. don't respond to any skin test antigens)

Is there a TB vaccine?

BCG vaccine give to infants in many higher TB area countries

Can a BCG vaccine cause a positive skin test?

Yes, but for only a few years; i.e. a positive test in an adult should not be ascribed to a childhood BCG vaccine

MOTT-related diseases are often seen in what individuals?

the immunosuppressed

MOTT can colonize where without causing disease?

the respiratory tract

MOTT is the cause of what?

most pulmonary disease, local lymphadenitis, bone and joint or skin/soft tissue infections

What type of immunity is essential against mycobacteria?

T cell immunity

What is another word for true leprosy?

Hansen's disease

Chronic infection of the skin, peripheral nerves and, in ________ _______, the nasal mucosa.

leprosy | lepromatous leprosy

How do peripheral nerves become palpable in leprosy?

Peripheral nerves are infiltrated by large numbers of AFB

What is the real cause of the loss of digits in leprosy?

Sensory deficits occur and thus trauma is the real cause of loss of digits

Lepromatous cases may exhibit what? What can it lead to if untreated?

classic leonine facies | can lead to hideous deformities if untreated

What immune response leads to tuberculoid leprosy? | What immune response leads to lepromatous leprosy?

Th1 | Th2

Why is the lepromatous leprosy associated with poorer health outcomes?

Because B cell immunity is stimulated

What happens to infectious state as treatment begins for leprosy? How long does one need to be treated for?

Nearly non-infectious as soon as treatment starts. | Need to treat for a long time.

What is the WHO operational definition for Leprosy?

Hypopigmented or reddish lesions with definite loss of sensation involvement of peripheral nerves (definite thickening and loss of sensation) Skin smear positive for acid fast bacilli

How does leprosy spread?

Via respiratory secretions.

What percentage of contacts develop leprosy?

only about 5%

What is the incubation period of leprosy? Describe disease progression speed.

Long incubation period 1-30 years | Slow disease progression

Although the distribution is mainly equatorial where else can we find leprosy?

Louisiana (Acadians), Texas and Hawaii

What is the diagnostic method of choice for Leprosy?

skin biopsy

What is an issue with growing M. leprae?

Cannot grow in culture yet

What is the cause of fish tank granuloma? | Does it occur in salt or freshwater aquariums?

M. marinum | Both

What is another word for the tuberculoid form of leprosy?

Paucibacillary

What is another word for the lepromatous form of leprosy?

multibacilliary