Mycobacteria and Nocardia Flashcards
- acid fast bacilli with unusual complex and lipid rich cell wall
- obligate aerobe
- slow growing
mycobacteria
tuberculous pathogens?
m. tuberculosis and m.bovis (extrapulmonary Tb)
non tuberculous pathogens?
m. kansasii in immunocompromised, MAC disseminated in AIDS
risk factors for Tb?
exposure to persons wit Tb, HIV infection, immunosuppressive therapy, homelessness, incarceration, alcohol, illicit drug use, diabetes, chronic pulmonary disease
properties of M. tb:
- _______ growth rate
- cell walls with high _____ content provides resistance to antibioitcs, dessication, complement, toxic oxygen species
slow
lipid
60% of the cell wall of m tuberculosis made up of?
mycolic acid/ lipids
transmission of TB:
- person to person via ________
- taken up by __________, via ___ and _____
- survive intracellularly by preventing?
small respiratory droplets
alveolar macrophages, LAM adhesin and C3b opsonization
phagosome lysosome fusion
in immunocompromised patients TB spreads to?
bone marrow, spleen, kidneys, CNS
pathogenesis of TB:
- what type of reaction?
- secretion of ______
- lysis of phagocytic cells by ______
- bacterial killing by activated ________
type IV delayed hypersensitivity reaction
IFN-gamma and cytokines
cytotoxic T cells
macrophages
- expressed by virulent strains of TB
- glycolipid of trehalose and two mycolic acid
- disrupts mitochondrial membranes
cord factor
latent TB infection
-______ formation of aggregates of activated macrophages, ________ that can fuse into multinucleated ________
granuloma
epithelioid histiocytes
Langhan’s giant cells
tubercle formation: large granulomas containing bacilli surrounded by T cells and macrophages encapsulated with ________
collagen
calcified primary granuloma
Ghon focus
low pathogen burden in TB?
self limiting infection and immunity
high pathogen burden in TB?
necrosis due to cytokine toxicity, activation of complement cascade, ischemia, hydrolytic enzymes
smaller than pea sized granulomas in TB?
cleared from bacteria by activated macrophages
larger necrotic or caseous granulomas in TB?
encapsulation with collagen/fibrin, survival of bacteria, reactivation in immunocompromised
early symptoms of pulmonary TB?
fever, night sweats, weight loss, malaise
later symptoms of pulmonary TB?
nonproductive cough, then productive with bloody sputum, chest pain, shortness of breath
primary TB?
- disease within 2 years of infection
- children
- heals spontaneously
secondary TB?
- post primary reactivation TB
- greater than 2 years post infection
- endogenous reactivation of latent infection
- pulmonary and extrapulmonary TB
- seedlings of TB bacilli, more likely with immunosuppression
- hematogenous spread to lymph nodes, GU, bone joints, meninges, GI tract
miliary TB
tuberculosis adenitis usually in the neck
scrofula
dx of TB with radiology reveals lesions where?
oxygenated parts of lungs
tuberculin (mantoux) skin test is a _______ hypersensitivity response, which screens for ____ TB by injecting _________
type IV delayed
latent
Purified protein derivative
in mantoux TB skin test, redness swelling and induration occur after _____ days, and patients are not positive until ______ weeks after infection
2-3 days
3-6 weeks
when reading tuberculin test, measure ______ only
induration
limitations of PPD tuberculin test?
anergy (Esp with HIV patients), recent TB infection, very young age, prior immunization, cross reactivity to other mycobacteria
alternative to tuberculin test for diagnosis of latent TB, measures M. tb antigens, more specific
IGRA: interferon gamma release assay
diagnosis of M. tb?
- acid fast stain of sputum
- auramine-rhodamine fluorescent staining of mycolic acid
- culture: definitive but slow, on lowenstein jensen media
- BACTEC: metabolism
- qPCR: good, also detects resistance for isoniazid and rifampin
first line drugs for TB active disease?
isoniazid (inhibits mycolic acid synthesis), rifampin, streptomycin, pyrazinamide, ethambutol (inhibits arabinoglactan synthesis)
candidates for TB prophylaxis?
positive tuberculin skin test + HIV infection, close contacts with infectious TB, chext Xray with previous TB, injection drug use
BCG vaccine contains live attenuated ________, most effective in children, but not recommended in US b/c it affects ________
M. bovis
surveillance
- transmission by aerosols, contact
- obligate intracellular pathogen
- infects skin, peripheral nerves (Schwann cells), eyes, mucous membrane, testes
- reservoir: humans, primates, armadillos
M. leprae
tuberculoid leprosy spectrum
- nerve damage?
- acid fast bacilli?
- Th1 CMI?
- Th2 humoral immunity?
2-40 yr incubation, neuropathies and enlarged peripheral nerves
- low amt acid fast bacilli
- high T cell mediated immunity
- low humoral immunity
lepromatous leprosy spectrum?
- acid fast bacilli?
- Th1 CMI?
- Th2 humoral immunity?
- high amt acid fast bacilli
- low T cell mediated immunity
- high humoral immunity, causes tissue damage
diagnosis of M leprae?
- acid fast stain of tissues
- lepromin skin test
- serology for PLG-1: phenolic glycolipid 1 - adhesin
drug therapy for m leprae?
dapsone: inhibits folic acid synthesis, check G6PDH
- reservoir: birds, mammals, soil, water
- transient colonization
- opportunistic pathogen (AIDS)
- multidrug combos: clarithromycin/azithrmycin, ethambutol, rifabutin
MAC
- tuberculosis like disease
- water and milk
- midwest and TX
m. kansasii
waterborne, subQ abscesses and skin ulcers
m. marinum
- gram positive, catalase positive aerobic actinomycetales
- form hyphae
- ubiquitous in decaying organic matter
- immunocompromised, avoid phagocytic killing due to secretion of catalase and SOD
- survive and replicate in macrophages, block phagosome lysosome fusion
- bronchopulmonary disease
nocardia
painless firm subcutaneous nocules
actinomycotic mycetoma
nodules along lympatics
lymphocutaenous disease
diagnosis of nocardia?
- gram positive, partially acid fast
- aerial hyphae
- antibiotic treatment: TMP-SMX
