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26 Cards in this Set

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What 2 main pt populations do you see Mycobacterium TB?

immigrants and HIV pts

In what population does immediate progression to active TB usually occur? How does it initially present?

kids -> presents as meningitis

How long does it take to detect M. tuberculosis using traditional means of identifying on solid growth media?

3-4 wks (due to TB's long generation time of 24 hrs)

What are the 2 more recent means of identifying M. tuberculosis from a culture?

1) Radiometric Growth Detection - bacteria metabolize radiolabeled palmatic acid to CO2 -- days until result



2) Gene probes - for 16s RNA - hrs until result

How long after exposure to TB does it take for a PPD test to turn (+)?

3-12 weeks (this is the amount of time it takes cellular immunity to ramp up a response)

What is the drug of choice for latent TB?

Isoniazid for 9 mths w/ monthly monitoring for hepatitis

How does mycobacteria evade host defense systems?

intracellular growth in macrophages

What percent of pts infected with TB will progress to active TB sometime during their lifetime?

15% - occurs during times of stress or immunocompromization

Strict Cut-off induration interpretation of PPD

15 mm - for non-high risk populations

Intermediate Cut-off induration interpretation of PPD

10 mm - for kids, immigrants, IV drug users, lab workers, illness, or converter (someone w/ and increase in induration of 10+ mm w/ in 2yr)

Low Cut-off induration interpretation of PPD

5 mm - for people w/ recent TB contact, fibrotic changes on X-ray, or immunosuppressed (HIV or organ transplant)

"Booster Effect"

individual was infected w/ TB a long time ago and their cellular-immunity has now waned causing their PPD test to fall below normal cut-offs. A new PPD test will boost their immunity against TB and cause a much larger response on the following test


(Why you must repeat PPD 1 week after initial test)

How should you treat active TB?

Start on a multi-drug regime (usually 4 - one being isoniazid). If pt fails to respond, always add more than one drug at a time to prevent selection for drug resistant strains

Effect of BCG vaccine on PPD test

Causes a false + that fades w/ time. If pt has had vaccine ask if they've had PPD - if they have and it was (-) then you can assume BCG effect has waned. If you get a + result, treat as a normal + workup

CDC control measures for TB infected pts

1) trx pt (most important measure)


2) Neg-pressure room isolation


3) healthcare workers wear masks



Continue precautions until there are no Acid-fast bacilli in sputum for 3 consecutive days and symp resolve

Mycobacterium leprae

Acid fast bacillis that lives in cool temp places on body. Spread via armadillo-to-human contact



Use phenolic glycolipid to live intracellular in macrophage, and lipoarabinomannan to prevent T cell proliferation

Int. Leprosy

very low # of AFB, hypo-pigmented skin patches, good recovery

Tuberculoid Leprosy

Few # of AFB, well-defined lesions w/ some nerve involvement



Due to robust Th1 response against infected macrophages

Lepromatous Leprosy

Many AFB, disfiguring nodules, nerves involved to cause sensory loss



Due to Th2 helper cells making Ab's that are useless against intracellular pathogen

Borderline Leprosy

Mix of tuberculoid and lepromatous leprosy. Most of pts

Trx for Mycobacterium leprae and 2 trx reactions that may occur

Dapson w/ either Rifamp or Clofazimine



1) Type 1 Reversal Rxn - increased inflammation at lesions and nerves


2) Type 2 Erythem nodosum Rxn - increase in cellular immunity in lepromatous pts causes mass cytokine release that cause inflam & papules


*both rxns treated w/ steroids

Which species of mycobacteria are contagious?

M. tuberculosis and M. leprae. All others are not contagious and only contracted from environment!!

Photochrome Non-TB Mycobacterium

*slow growers (2+ wks) that make orange pig when light is shined on them



. M. kansasii - common in midwest (kansas!), look like beaded bacilli, lung infections in immunocomp.



. M. marinum - painless/ulcerating papule after a cut is contaminated w/ salt water

Scotochromes Non-TB Mycobacterium

*slow growers (2+ wks) that make orange pig.



. M. gordonae - cause infections in immunocomp when they drink contaminated tap water

Nonchromogenes Non-TB Mycobacterium


and their trx

*slow growers (2+ wks) w/ no pig.



. M. avium-intracellare - most common NTM! Cause a lung infection that's similar to TB in symp and on X-ray. Can disseminate in AIDS pts w/ CD4 < 50



Trx = Clarithromycin and azithromycin

Rapid Growing Non-TB Mycobacterium

*look like diphtherioids on Gm stain, cause cutaneous infections after trauma or surgery



Include: M. abscessus, M. fortuitum, M. chelonae