Mycobacteria Flashcards
What is unique about the cell walls of mycobacteria?
High lipid content, gram-positive but they repel analine dyes so they may appear beaded upon staining
What kind of culture is used for mycobacterium leprae?
None, they are non-cultivable
What, specifically, does the TST test look for?
A cell-mediated immune response to tuberculosis
What conditions particularly predispose a person to developing active Tb disease?
Immunosuppression - aging, HIV infection, glucocorticoid use, etc
From 1985 to 1992 the Tb rate in the US actually increased. Why?
Immigration from countries with high Tb rate, AIDS, injection drug use, curtailment of public health programs
Where do Tb bacilli replicate?
In macrophages
Ghon Focus
A Tb lesion, typically in the subpleural area of mid lung created by the granulomatous response
Ghon complex
Peripheral ghon focus (a Tb lesion) with involved hilar lymph nodes
Where in the lung do progressive primary and secondary (cavitary) tb infections occur respectively?
Progressive primary - mid lung, Secondary - apical posterior sections, upper lobes
Miliary tuberculosis
Infection at multiple sites with characteristic small, yellowish lesion (resembles a millet seed)
Besides the lung, where are common sites of miliary Tb infection?
Lymph nodes, kidney, adrenals, marrow, spleen, liver
Why is secondary Tb infection also called Cavitary tb?
The immune response leads to tissue necrosis and cavitation
Common symptoms of Tb infection
Low-grade fever, night sweats, weight loss, productive cough, hemoptysis (blood in sputum)
Does erythema (redness) alone at TST test injection site indicate a positive test?
No, requires induration of a specific diameter
What are some bacteria included in the mycobacterium tuberculosis complex?
Mycobacterium tuberculosis, Mycobacterium bovis (BCG vaccine), Mycobacterium ulcerans, and Mycobacterium Africanum
Which bacteria in the mycobacterium Tb complex are included in the runyon classification and what are the groups of the runyon classification?
Includes all besides Mycobacterium Tuberculosis. Group 1 - Photochromogens, Group 2 - Scotochromogens, Group 3 - Nonphotochromogens, Group 4 - Rapid growers
What Runyon group is Mycobacterium Kansasii in, what type of infection does it produce, where is it common, and what do you treat it with?
Is a Group I (Photochromogen), produces infection similar to Tb, seen in midwest, treat with anti-Tb drugs
What will likely be in the history of someone infected with mycobacterium marinum?
Cut their hands in salt or fresh water, or have recently handled fish
What runyon group is Mycobacterium Avium-Intracellulare-Complex in, who does it particularly infect, and what do you treat with?
Group II (Scotochromogens) and some in Group III, esp infects HIV-positive pts and those with lung disease, difficult to treat (not susceptible to anti-Tb drugs)
What runyon group is mycobacterium haemophilum in, who in particular does it infect, what does it require?
Is in Group 3 (nonphotochromogens), infects immunosuppressed, requires iron ions to grow
What type of infections do the Runyon Group 4 organisms cause and give 3 organisms in this group
Skin infections in immunocompromised pts. Mycobacterium fortuitum, Mycobacterium chelonae subsp chelonae, Mycobacterium chelonae subsp abscessus
For what type of bacteria can you not use a swab specimen and why?
Mycobacteria, due to hydrophobicity they cling to swab material and dont get into culture
Culture media for mycobacteria
Lowenstein-Jensen (LJ) and liquid media (albumen based)
Difference between concentrated and direct smear specimens
Concentrated are digested, decontaminated (if necessary) and centrifuged. Direct are applied straight to slide
