Mycobacterium Flashcards
Mycobacterium tuberculosis is acid-fast due to high ________ content in its cell membrane
Mycolic acid
M.tuberculosis is an obligate _______ that replicates within ________
Aerobe; macrophages
Dye used for detection of TB
Carbol fuschin dye
Virulence factors associated with TB
Cord factor — membrane glycolipid, protects from host responses; release cachectin —> weight loss
Sulfatides — sulfolipids that prevent phagolysosome fusion (protect from lysosomal hydrolases, allow intracellular survival)
Siderophore — iron acquisition
What part of the lung is affected by primary vs. secondary TB?
Primary — middle or lower lobes
Secondary — upper lobes
Presentation of primary TB
Typically affects middle or lower lung lobes
Most common sx = low grade fever (usually no other sx); CXR shows hilar LAD, can develop pleural effusions
Caseating granulomas characterized by central necrotic zone, walled off by macrophages and lymphocytes; Ghon complex
Usually resolves by fibrosis of lung tissue
_____ TB occurs when dormant bacteria are contained within walled off foci
Reactivation is associated with the use of __________ inhibitors
Latent
TNF-alpha
Type of TB characterized by diffuse hematogenous spread to multiple organs; may present with cough, hemoptysis, night sweats, etc., and is potentially fatal
Miliary TB
Disease resulting from progressive primary OR reactivation/secondary TB involving infection of the vertebral column (typically lower thoracic/upper lumbar)
Pott disease [Tuberculous spondylitis]
Vaccine that may cause positive result on PPD
Bacille Calmette-Guerin (BCG) vaccine
Morphology of TB
Weakly gram + rod, non-motile, aerobic
Typically after an individual is infected with M.tuberculosis, there is healing by _____ and/or ______
Fibrosis; calcification
Typically after an individual is infected with M.tuberculosis, there is healing by fibrosis and/or calcification.
If this does NOT occur, the patient will have _____ _____ TB
Primary progressive
3 patterns of primary progressive TB
Primary caseous pneumonia — Gohn complex expands to entire lobe or segment, caseating necrosis, consolidated appearance
Tuberculosis bronchopneumonia — secondary to bronchogenic spread to entire lung parenchyma, patchy foci
Miliary tuberculosis — secondary to hematogenous spread, multiple nodules, millet seed appearance, spread across entire affected organ (liver, kidneys, meninges, spleen)
Sx and CXR findings associated with secondary TB (aka reactivation TB)
Insidious sx: fevers, chills, cough (+/- hemoptysis), weight loss, etc.
CXR: apical and posterior segment involvement, pulmonary cavitation present
If you suspect a patient is presenting with secondary TB, what are 3 tests that should be done next?
CXR
PPD skin test (Mantoux)
Morning sputum culture
PPD reaction sizes are categorized at >5 mm induration, >10 mm induration, >15 mm induration, and anergy.
In what situation(s) would a >15 mm induration be considered positive?
Healthy individual >4 with low likelihood of true TB infection
PPD reaction sizes are categorized at >5 mm induration, >10 mm induration, >15 mm induration, and anergy.
In what situation(s) would a >10 mm induration be considered positive?
Pts with clinical conditions that INCREASE risk of reactivation — silicosis, DM, chronic renal failure w/dialysis, malignancies (leukemia, lymphoma, lung, head/neck), malnourished, IV drug abuse
Children <4
From country with high prevalence
Residents/employees in high risk setting — jail, healthcare facilities, mycobacterium labs, homeless shelters
PPD reaction sizes are categorized at >5 mm induration, >10 mm induration, >15 mm induration, and anergy.
In what situation(s) would a >5 mm induration be considered positive?
HIV
Close contact with actively infected person
CXR with fibrotic changes consistent with TB
Immunosuppression (TNF-a inhibitors, chronic glucocorticoids, chemotherapy, organ transplant)
Describe PPD skin test
Aka Mantoux tuberculin skin test (TST)
Intradermal injection read within 48-72 hours
Made from PURIFIED PROTEIN of M.tuberculosis — will not cause infection, will illicit a reaction if previous exposure
The BCG vaccination is made from ______; it is given to kids and individuals exposed to TB or those that live in high prevalence area
M.bovis
What are some things that might cause false positive PPD test?
Previous BCG vaccine
Infection w/ nontuberculosis mycobacterium
Incorrect administration of PPD
Incorrect interpretation
What might cause false negatives on PPD?
Anergy
Recent TB exposure (not enough time to generate response)
Very old TB
Age <6 months
Recent live virus vaccination or infection with virus (measles, chicken pox)
Overwhelming TB infection
A PPD skin test is an example of what type of hypersensitivity reaction?
Type IV HSR — delayed (T cells)
Which of the following is the initial staining that should occur to SCREEN for M.tuberculosis?
A. Ziehl-Neelsen stain B. Methenamine stain C. Auramine-rhodamine stain D. India ink stain E. Gram stain
C. Auramine-rhodamine stain
Utilizes fluorescent microscopy — MOST SENSITIVE for AFB organisms!!
[Ziehl-Neelson and Kinyoun are confirmatory AFB stains, more SPECIFIC for TB]
The benefit of nucleic acid amplification testing (NAAT) is to detect resistance to which drug(s) in the mainstay TB treatment regimen?
Rifampin and INH
What type of isolation room should pts be admitted to when they have confirmed active TB?
One with negative-pressure ventilation — minimizes risk of aerosolized transmission throughout hospital
A pt with a hx of receiving the BCG vaccination returns with a positive PPD skin test. What is the next step?
Interferon-gamma release assay (aka Quantiferon gold or T-spot)
This will give more definitive result
Which of the TB medications may cause the adverse effects of blurry vision, seeing “flashing lights”, diminished peripheral vision, decreased color vision, etc.?
Ethambutol
A patient diagnosed with active tuberculosis (latent) can expect 4-drug regimen for what duration of time?
6 months; requires monitoring with sputum samples
A TB patient presents with pleural effusions; what is the most likely finding on aspirate of the fluid?
A. Elevated amylase B. Positive adenosine deaminase C. High triglycerides D. >100,000 RBC/mcL E. Clear, translucent fluid
B. Positive adenosine deaminase — indicative of TB
What general tests/labs/etc are included in the workup for M.tuberculosis?
CXR
PPD (mantoux)
NAAT-TB and NAAT-R
Sputum culture
Interferon-gamma release assay (for BCG vaccinated individuals and positive PPD with low likelihood of TB)
____ = calcified primary focus with hilar lymphadenopathy on CXR
_____ = calcified primary foci in peripheral lung tissue
Ranke
Ghon
General steps in management of active TB
4 drug therapy: INH, rifampin, pyrazinamide, ethambutol
Treat for at least 6 months; follow with sputum cultures, CBC, CMP
DOT preferred
If admitting — place in negative pressure isolation room
Drug therapy utilized in drug-resistant forms of TB
Streptomycin
In latent TB, ______ is given for _____ month(s)
INH; 9
Populations at highest risk for TB
Malnourished Homeless Overcrowded areas HIV/immunosuppressed Living in endemic areas
Extrapulmonary manifestations of Tb
Most common is lymphadenitis (scrofula)
Pleural effusions (generally seen in primary progressive TB)
Meningitis
Tuberculous spondylitis (Pott disease)
Intestinal TB — secondary to contaminated milk ingestion (think M.bovis)
Morphology of mycobacterium kansasii
Acid fast bacillus
Nonmotile
T/F: mycobacterium kansasii is spread via person-person contact
False — it is picked up from the environment
Patient populations in which you see mycobacterium kansasii
Older pts with underlying lung disease or long time smokers
M»W
Endemic areas for mycobacterium kansasii
Midwest and southwest US
Sx and CXR findings with mycobacterium kansasii
Sx: very similar to TB, but follows longer course; fevers can be present 17% of the time
CXR: Older smokers (cavitary lesion in apex), women with chronic cough (bronchiectasis in mid-lung zone), pneumonitis hypersensitivity s/p exposure
Tx and prognosis of mycobacterium kansasii
Tx: Rifampin, INH, and ethambutol for at least 18 months
Left untreated = 50% mortality
