Micro: Tuberculosis Flashcards
Mycobacterium tuberculosis is extracellular or intracellular ?
Intracellular.
What constituent of M.tuberculosis cell wall (yes there is a cell wall) makes a Gram stain unlikely ?
Mycolic acid !
What protective purpose does mycolic acid serve ?
resistant to detergents and common antibiotics
Protects the cell from desiccation (does not dry out)
What culture media will M.tuberculosis grow on ?
Lowenstein-Jensen Agar (gold standard for diagnosis but not practical due to long growth period)
What diagnostic stain is used to identify M.tuberculosis ?
Acid Fast (Ziehl Nelson stain)
What is Cord Factor ?
surface glycolipid which blocks macrophage activation by IFN-γ, induces secretion of TNFα and causes Mycobacterium tuberculosis to form cords in vitro
Allows for anti-microbial resistance to many antibiotics.
What causes tissue necrosis in TB ?
Host immune response
Describe the signs and symptoms associated with TB
Mild fever , chest pain, cough (productive and often bloody), Fatigue, malaise, weight loss and sweating.
Where is M.tuberculosis endemic to ?
Southeast asia
Sub-saharan africa
Eastern Europe
Primary tuberculosis
Initial cause of tuberculosis disease
Secondary tuberculosis
reactivation of a latent infection
Disseminated tuberculosis
involves many (milliary spread)
What cells does m.tuberculosis infect intracellularly ?
Alveolar macrophages (much like legionella)
Activation and recruitment of alveolar macrophages leads to the formation of …
Tubercle (Granuloma)
Caseous lesion
Cheese like interior to a granuloma
Ghon complex
Calcified casesou lesion (show up in chest x rays well)
Tuberculous cavities
Tubercle that has liquified and formed and air-filled cavity in which bacteria can spread from
Reactivation tuberculosis (secondary) Aspergillus likes these cavities !
Screening
Tuberculin (Mantoux Test)
+ Tuberculin. Whats next ?
Chest X-ray for signs of tubercles
Microscopy of sputum (Acid Fast staining of sputum)
3rd step is TB diagnosis (not entirely necessary)
Culture on Lowenstein Jensen.
Specific but extremely slow .
What are the 4 main drugs used in treatment of tuberculosis ?
Isoniazid
Rifampin
Ethambutol
Pyrazinamide
Describe the “Preferred” Regimen for treating TB
Initial: Daily INH, RIF, PZA and EMB for 56 doses (8 weeks)
COntinuation: Daily INH and RIF for 126 doses (18 weeks)
Describe the Alternative Regimen for TB treatment
Intial : Daily INH, RIF, PZA and EMB for 14 dosed (2 weeks) the twice weekly for 12 doses (6 weeks)
Continuation: Twice weekly INH and RIF for 36 doses (18 weeks)
MDR-TB
Multi-drug resistant TB –> Resistant to Isoniazid and Rifampin ! (Uh Oh)
XDR-TB
Extremely drug resistant TB–> Resistant to isoniazid , rifampin and at least one of the other two (ethambutol or pyrazinamide)
DOTS
Directly Observed Treatment Short Course
Why do we not give out the Bacille Calmette Guerin vaccine in the US ?
We have such a low occurrence of TB and the vaccine would render the Mantoux test ineffective for screening.
BCG is a mycobacterium bovis strain.
Describe Micobacterium Avium Complex
Mixture of : Mycobacterium Avium and Mycobacterium Intracellulare
Weakly G+
Acid Fast Aerobic Rods (Mycolic acid in cell wall)
Who typically contracts MAC ?
Immunocomrpromised patients
Chronic Pulmonary disease.
Primary MAC
Similar to primary TB
Secondary MAC
Dissemination to all organs and blood stream !
Who typically get s 2nd MAC ?
AIDS patients with low CD4+ T-Cell counts ( <50 Cells/ml)
How do you prevent MAC infection in AIDS patients ?
Constant prophylaxis with
Clarithromycin
Azithromycin
Describe the lab diagnostics of Nocardia
Gram +, Aerobic
Weakly Acid fast
Branching Filaments (Branched long Rods)
Normally found in the soil
CUlture: BLood or Chocolate Agar
Who is at risk for nocardiosis ?
Immunocompromised
Renal transplants
Where does nocardia spread to after forming lung abscesses ?
Brain and kidney (renal patients at increased risk)
TOC for Nocardia
IV Trimethoprim-sulfonhexamide (Bactrim)
Linezolid
