Mycobacteria

Front 1

What is the bacteriology of Mycobacterium?

Back 1

Mycobacterium: Slim, weakly Gram (+) bacilli, acid-fast (red), req/ heat to stain through cell wall lipids, non-motile, strict aerobes, classically cause chronic granulomas (high infectivity but low virulence)
-------------------------------
Mycobacterium tuberculosis in sputum stained by the acid-fast technique. The mycobacteria retain the red carbol fuchsin through the decolorization step. The cells, background, and any other organisms stain with the contrasting methylene blue counterstain

Front 2

What composes the Mycobacterium cell wall?

Back 2

60% is lipid making it very hydrophobic & resistant to drying & resistant to chemical agents. It is a heterogeneous bilayer.

Majority of this is Mycolic acid which causes it to gram stain poorly but once it is retained it is acid fast in resisting washing out the stain

Front 3

How do you get a 1y TB infection?

Back 3

Typically from Aerosol from active TB cases. UV kills microbe, so prolonged exposure in dark enviroment harbors spread. This will then deposit in lung, be ingested by macrophage leading to granuloma formation If exposed 10-30% become infected.

Front 4

What is the 1y pneumonia pathogenesis?

Back 4

Mycobacterium tuberculosis deposits in lower lobe -> TB is ingested by alveolar macrophage -> TB mycolic wall permits intracellular proliferation/survival. -> infection spreads hilar lymph, blood -> Spread stops once DTH/CMI forms tubercule that is walled off.

Front 5

What does reactivation or latent tuberculosis look like?

Back 5

The same as a 1y infection. This was caused by reactivated TB. Notice the fibrosis that surrounds the tubercle. Their is likely more fibrosis in latent.

This ability to decrease metabolism is a virulence factor to allowing it to persist.

Front 6

How is 1y TB infection different from latent infection?

Back 6

A weakened T cell response or immunocompromised state leads to reactivation from the dormant state. No initial inoculation from another infected individual is required.

Front 7

What is the pathogenesis of reactivation or latent tuberculosis?

Back 7

A decreases in T cell response(AIDs, age, stress) -> reactivation of apex located tubercles -> TB replication results in cavitation -> TB, necrotic debris, blood are released to bronchi -> active TB that is highly contagious

10% TB will reactivate. TB may spread to bone or CSF

Front 8

What is the classical appearance of 1y tuberculosis on Xray?

Back 8

Ghon complex - benign healed 1y TB lesion. Calcified hilar lymph node (upper and medial) & granuloma (lower and lateral)

Calcification is after recovery from infection
(where located in this image)

Front 9

What does the Tuberculin PPD test measure?

Back 9

Measures the DTH response to PPD that screen for active and inactive TB cases. PPD is injected intra cutaneous

May show positive for foreigners who received different type of vaccine (BCG)

Front 10

When is a Tuberculin test measured? What constitutes a positive test? What is the follow up?

Back 10

Measure 48-72H post injection

Measure diameter of induration, not erythema. A positive test is >10mm. It is also dependent on a proper DTH/CMI immune response (may not work in AIDs pts)

Confirmationof a positive test is: CXR, clinical symptoms. Will be + if EVER infected

Front 11

Can a false negative occur for a TB test?

Back 11

Yes, in the case that the pt is in the pre-DTH stage, Lost immunity to TB, Anergic, has AIDs or is Immunocompromised in any way.

Front 12

What is a method of diagnosing TB from sputum? What is the sensitivity?

Back 12

Top - acid fast stain of sputum is important (acid fast bacillus)
Bottom - fluorchrome stain showing yellow Mycobacterium TB organisms

Only about 65% sensitive.

Front 13

What are the laboratory methods for diagnosing tuberculosis?

Back 13

Culture on special media - 3+ weeks to culture. Often used to determine susceptibility.

Quantiferon gold TB test - measures IFN-gamma produced by T cells in while blood after 2 TB Ags are added to the blood. Measures active/latent TB. ($$$)

RT-PCR from sputum and can detect rifamypin gene resistance too!

Use giant rats

Front 14

What is the pathogenesis of 1y and reactivation tuberculosis?

Back 14

Tuberculosis. A. Primary tuberculosis. Mucobacterium tuberculosis is inhaled in droplet nuclei from an active case of tuberculosis. Initial multiplication is in the alveoli with spread through lymphatic drainage to the hilar lymph nodes. After further lymphatic drainage to the bloodstream, the organisms are spread throughout the body.

B. Alveolar macrophage. The two-front battle being carried out between A and C is shown. Ingested bacteria multiply in the nonactivated macrophage. (1) TH1 cellular immune responses attempt to activate the macrophage by secreting cytokines (interferon gamma [IFN-]). If successful, the disease is arrested. (2) Inflammatory elements of delayed-type hypersensitivity (DTH) are attracted and cause destruction. If activation is not successful, disease and injury continue.

C. Reactivation tuberculosis. Reactivation typically starts in the upper lobes of the lung with granuloma formation. DTH-mediated destruction can form a cavity, which allows the organisms to be coughed up to infect another person.

Front 15

What is the epidemiology of mycobacterium tuberculosis? Transmission? dose, time, at risk populations & why?

Back 15

p2p transmission
low infecting dose w/ long duration exposure

At risk population: prison, low socioeconomic, nursing home, high population density & closed enviroment & absence of TB killing UV light,

50% new cases immigrants

Front 16

Describe histologically a tuberculous granuloma.

Back 16

Tuberculous granulomas.

A. Early granuloma with lymphocytes, epithelioid cells and fibroblasts organizing around a central focus. The multinucleate giant cell in the center is typical of granulomas but not exclusive to Mycobacterium tuberculosis.

B. Multiple granulomas surround and invade a vein near the lung hilum. Central degeneration is starting to appear and will eventually become caseous necrosis.

Front 17

Is Mycobacterium Tuberculosis susceptible? How is it treated in gen population? In healthcare workers w/ changed PPD test

Back 17

Many multidrug resistant strains

Use multidrug regimens

Treatment is multidrug until susceptibility is known and use DOTs (direct observed treatments) to increase adherence and decrease resistance formation

Use INH prophylactically in skin convesion test in healthcare workers for 1year.

Front 18

What is the challenge in culturing mycobacterium tuberculosis?

Back 18

Very slow growing - Doubling time 12-24H (due to complex cell wall). Culture may take 3-6wks and requires special media.

Front 19

What is the immune response to Mycobacterium Tuberculosis?

Back 19

DTH - destructive - NK cells recognize inactivated macrophages & kill them. This releases the mycobacteria and leads to granuloma formation

CMI - immune component - CD4/CD8 T cells & activated macrophages release INF-gamma which increases MHC1 expression.

Humoral response little importance because intracellular pathogen

Front 20

How does a 1y TB infection heal?

Back 20

Lesion (tubercle) heals by fibrosis
Microbe is slowly killed by activated Macrophages
TB persists in aerated upper lobes w/ low lymphatic drainage

Front 21

What are the issues surrounding the TB vaccine?

Back 21

BCG - effective only in children. Not really in adults
BCG is live attenuated vaccine of mycobacterium bovis

Causes conversion of PPD which makes screening hard

BCG not recomended in US

Front 22

What is miliary TB?

Back 22

Disseminated TB infection. Name derives from CXR which resembles millet seed spread throughout the lungs.

Occurs as complication in 1-3% of cases.

Front 23

What are the symptoms of TB? A critical complication?

Back 23

Cough, hemoptysis, night sweats & fever, weight loss (consumption)

CNS infection predominately in children (why give BCG vaccine)

Front 24

What mycobacterial species cause clinical manifestations similar to tuberculosis and how can these be differentiated from TB?

Back 24

They are distinguished by biochemical rxns & characteristics (pigment formation)

Mycobacterial Avium - Clinically indistinguishable from mycobacterium TB. Major issue in AIDs pts.

Mycobacterial Bovis - from unpasteurized milk. Causes GI TB, or lung TB if inhaled. Will cause +PPD test too!

Mycobacteria Kansasii

Front 25

What is the epidemiology of Mycobacterium Leprae?

Back 25

Generally not life threatening, just disfiguring & disabling.
Significant issue in developing nations

Front 26

What are the 2 extremes in the spectrum of clinical manifestation of Mycobacterium Leprae infections?

Back 26

Lepromatous Leprosy - more severe
-Has low/no CMI response w/ poor development of granulomas. High # AFB in tissue & bloodstream, More contagious, High Ab levels

Tuberculoid - minor severe
Has CMI response to AFB granuloma, Few AFB in tissue, Low Ab, Rapid nerve damage, Not contagious (usually)

Front 27

What are the clinical manifestations of Lepromatous Leprosy?

Back 27

Slow deteriorating nerve damage -> anesthesia & loss digits & tissue damage & leonine facial features

------------------------------------
Lepromatous leprosy. Note the cutaneous plaques, infiltrates, and loss of eyebrows. Scrapings of the ear lobes would reveal numerous acid-fast bacilli. This advanced case will still respond to appropriate chemotherapy.

Front 28

How does the clinical manifestations and diagnosis similar and different in leprosy and tuberculoid?

Back 28

They differ in strength CMI response, Ab levels, AFB counts, & contagious levels

---------------
Lepromatous leprosy (severe) - Loss of fingers due to not feeling wounds on the hands.

Front 29

What are the clinical manifestations of Tuberculoid leprosy?

Back 29

Tuberculoid - minor severe
Has CMI response to AFB granuloma, Few AFB in tissue, Low Ab, Rapid nerve damage (CMI response), Not contagious (usually)

Anesthetic effect is localized. Later may lose motor function.

Front 30

What is the source and route of transmission of leprosy? Where is it cultured?

Back 30

Humans are the ONLY resovoir and source of M Leprae (nasal discharge, break skin/mucous membranes, blood to skin/nerve)

Long incubation period

Cultured in:
mouse footpad
armadillos

Front 31

What is the pathogenesis of M leprae?

Back 31

M leprae is obligate intracellular parasite -> replicate skin macrophage & Schwann cells -> Chronic granulomatous disease of skin, peripheral nerves, & superficial tissue. -> peripheral nerves are invaded and anesthesia results.

Front 32

How does the pathogenesis of M leprae in tuberculoid & lepromatous differ?

Back 32

Tuberculoid has a strong CMI response -> contains infection to localized region -> Nerves are palpable and damaged leading to patches/lesions of anesthesized, hypopigmented & hairless skin

Lepromatous has weak CMI response -> uncontained microbe travels to cooler regions (face, nose, testis, extremities) -> More effected regions

Front 33

What is the bacteriology of Mycobacteria Leprae?

Back 33

Weakly acid-fast bacillus
Obligate intracellular parasite
Slow growing doubles in 11-13days
Outer wall rich in mycolic acid
Only grows in armadillos & mouse footpads

----------------------
High # of AFB Mycobacterium Leprae in tissue section

Front 34

What are the layers in order of the Mycobacteria cell wall?

Back 34

Cell membrane - Peptidoglycan Mycolic acids.

LAM, lipoarabinomannan.

Front 35

Summary of mycobacterium species

Back 35

Front 36

How are mycobacterium similar/different from other gram (+) organisms?

Back 36

Differ in that high amounts of mycolic acid that makes it acid fast, hydrophobic

Front 37

How is mycobacterium leprae diagnosed?

Back 37

From acid fast smears of
skin slits/biopsies, nasal mucosa, ear lobe

Lepramatous pts have high # AFB and are easier to dx.

Tuberculoid pts may be dx clinically or through skin biopsies.

Front 38

How is mycobacterium leprae treated?

Back 38

Tx is very effective & cheap
(multi to prevent formation of resistance)
1. Sulfones (dapsone) - some resistance from misuse
2. Rifampin
3. Clofazimine

Tx should not be stopped even if rx reactions occur

Front 39

What is the source of tuberculosis like pathogens?

Back 39

Environment
M. Bovis - unpasteurized milk
M. Avium 0 birds, mammals in soil & water

Front 40

What is the importance of determining non mycobacterium tuberculosis- TB diseases?

Back 40

They are generally harder to treat and have more Abx resistance.

Front 41

What is another significant and frequent TB infection?

Back 41

Mycobacterium Avium-Intracellular Complex (MAIC)
- A group of related AFB microbes that are very similar
- Cause disease in adults, major issue in AIDs
- Prognosis is grave when diagnosed with MAIC
- Highly resistant & hard to treat