RHS19 - Respiratory Tract Infections 7 Flashcards
Describe how you can tell the difference between a pneumonia caused by mycoplasma pneumoniae and one caused by chlamydophila pneumoniae.
- Clinically they present identically although chlamydophila pneumoniae occurs more frequently in “middle age” children (4-11yo)
- Upon microscopy, chlamydial inclusion bodies can be seen in the infected cells (refer to image)
- Serology or PCR is the only way to be certain
Describe the life cycle of chalmydophila pneumoniae and name what other life cycle is similar to it.
- An elementary body (EB), which is not metabolically active but is infective enters the cell via endocytosis, the endosome does NOT fuse with a lysosome
- EB transforms into a reticulate body (RB) which is metabolically active and replicates itself via binary fission
- The RBs transform into EBs and exit the cell via exocytosis, in chlamydophila pneumoniae, or via lysis of the cell, in chlamydophila psittaci
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What type of bacteria is legionella pneumophila? What are its virulence factors?
- Gram Negative
- Facultative Intracellular (alveolar macrophages)
It’s primary virulence factor is its capacity to be phagocytosed and survivie intracellularly by preventing phagosome-lysosome fusion.
How does legionella pneumophila cause damage?
Primarily via the host inflammatory response
What clinical features would suggest a pneumonia was actually Legionnaire’s disease?
- Recent exposure to a possibly contaminated water source
- Pontiac Fever (a self-limiting fever)
- Hematuria
- GIT involvement (diarrhea)
- CNS involvement
What lab diagnostics are used for legionnaire’s disease?
- It only grow on buffered charcoal yeast extract (BCYE) agar
- Visualization of small black opaque rods in and out of cells on a silver stain (refer to image)
- A urinary antigen test that checks for L. pneumophila serogroup 1 (the cause of >80% of infections)
- If urinary antigen testing is negative but Legionnaires’ is still suspected, then a respiratory culture is required
How is legionnaries disease transmitted?
Legionella pneumophila usually resides in amoebae in water. Transmission typically occurs when this water become aeroslized and inhaled
What kind of bacteria is mycobacterium tuberculosis?
- Acid fast bacilli
- Aerobic
- Non-spore forming
List the virulence factors of mycobacterium tuberculosis
- Mycolic acid (a sulfolipid) in the cell wall prevents the oxidative burst in phagocytic cells and inhibits phagosome-lysosome fusion, allowing M, tuberculosis to proliferate intracellularly
- Lipoarabinomannan (LAM) in the cell wall along with the capability to secrete SOD allows the cell to resist lysosomal enzymes and reactive oxygen species
Describe the various routes a TB infection can take
- After infection, the bacteria could be eliminated from the body
- After infection, the immune system contains the bacteria within a granuloma. This is known as latent TB and is the most common route. If the system becomes immunocompromised, the latent TB can become reactivated
- The immune system is unable to contain the initial infection and active TB starts.
How is TB transmitted? What clinical features would suggest a pneumonia was caused by TB
Transmittd by droplet nuclei and dust
- Dry cough for >2-3 weeks that may eventually produce blood tinged sputum
- Weight loss (like cachexia)
- Fatigue
- Mild Fever
- Chills, Night Sweats
- Other organ systems are involved, particularly the CNS (meningitis)
What other diseases is TB closely associated with and why?
HIV-AIDS
The ability to contain TB infection is largely dependent on the CD4+ helper T cells that produce γ-interferon. The population of the cells is largely reduced in HIV-AIDS
What are the lab diagnostics for Mycobacterium tuberculosis?
- Lowenstein-Jensen agar or Oleic acid-albumin broth is needed to culture (M. tuberculosis requires high protein content). They appear as wart-like cells in these cultures (left image)
- Ziehl-Neelsen stain (acid fast stain) of sputum allows visualization or dark bacilli. (right image)
- Purified Protein Derivative Test (PPD) checks for active/latent TB or previous TB vaccination
- TB QuantiFERON blood test checks for active/latent TB
How is a PPD test read?
48-72 hrs after injection, the site is inspected for induration (hardening)
>15mm of induration indicates the presence of active/latent TB or a previous TB vaccination
<5mm of induration indicates the absence of active/latent TB and previous TB vaccination
5-10mm - diagnosis depends upon risk factors
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