Pathogens Associated with Atypical Pneumonia Flashcards Preview

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*** What are the 3 pathogens associated with atypical pneumonia?

1. Mycoplasma pneumoniae
2. Chlamydia pneumoniae
3. Legionella


*** What does Mycoplasma require to grow?

- it is an obligate aerobe that requires STEROLS because there is no cell wall.
- it grows in hot springs and acid outflows of mining wastes.


What antibiotics are used to treat mycoplasma?

Erythromycin (macrolide), Tetracyclines, or Fluoroquinolones.
*because it lacks a cell wall, no vaccine is available.


How do we diagnose Mycoplasma?

PCR because otherwise culture takes weeks.


Is mycoplasma contagious and how do we treat?

- It is moderately contagious (sneezing or coughing) and treat with antibiotics if suspicious (without culturing bc it takes too long).


In what group of people is mycoplasma a cause of pneumonia?

children and into 30s by binding to neuramininc acid (key component of sialic acid of our glycoproteins) on respiratory epithelium via P1 adherence proteins.
*antibodies can inhibit this attachment :)


Are humans the only known reservoir for Mycoplasma?



How does Mycoplasma differ from other pneumonias?

it is limited to respiratory mucosa that lines the airways and does NOT involve the alveoli!
- causes bronchopneumonia with mononuclear cells infiltrating around the bronchi (NOT a lobar process).


How does mycoplasma cause damage to the host?

- it is not the bacteria, but rather the HOST RESPONSE that causes damage to the respiratory epithelial cells, impairing ciliary function.
- Extrapulmonary complications= HEMOLYTIC ANEMIA (50%) where IgM binds to RBCs at cold temps (cold hemagglutinins), thromboembolic complications, meningoencephalitis, or cerebellar ataxia.


What are the symptoms of pneumonia caused by Mycoplasma?

- non-productive cough (ronchi and rales on auscultation).
- non-purulent sputum production
- chest x-ray= variable infiltrate, patchy bronchopneumonia in lower lobes.
- UNUSUAL but does happen occasionally: macropapular rashes or erythema multiforme (Stevens-Johnson syndrome).
- Target lesions on palm (type IV hypersensitivity)


Can some pts with mycoplasma pneumoniae develop ARDS (acute respiratory distress syndrome)?



*** What type of bacteria is chlamydia? (sketchy)

very small gram negative (poor staining and weak LPS on outer membrane) obligate intracellular bacteria (once thought to be a virus).


What is the key energy source of chlamydia?

- tryptophan (key amino acid for making serotonin).
- uses ATP made from host mitochondria


Where can you encounter chlaymdiae?

- C. psittaci can be contracted by bird owners causing Psittacosis and can be deadly!


Do most people have antibodies to C. pneumoniae?

YES meaning they were exposed at some point in time.


How does C. pneumoniae reproduce?

- extracellular= infectious (elementary body; EB).
- intracellular= metabolically active (reticulate body; RB).


Why can't your body rid itself of C. pneumoniae in its EB form when it enters the cell?

bc it is located inside a vacuole, and it keeps the pH high within this vacuole, preventing vesicle-lysosome fusion. It then transforms into the RB form killing the epithelial cell bc it uses its nutrients.


What are the unique clinical manifestations of pneumonia caused by C. pneumoniae?

unshakable non-productive cough. It is often a co-pathogen with step pneumo.


What are the damaging host response chemicals to C. pneumoniae's hsp60 and LPS?

IL-1, TNF-a, and IFN-y


How do we diagnose C. pneumoniae?

- serologically (most common) IgM, IgG, IgA= four-fold rise in titer is positive.


How do we treat C. pneumoniae pneumonia?

for the RB (intracellular forms) it must pass through 4 membranes ( host cell, inclusion membrane, chlamydial outer membrane, chlamydial cytoplasmic membrane)= AZITHROMYCIN or fluoroquinolones or tetracyclines.


*** What is Legionella? (sketchy)

- gram negative, aerobic bacilli that is motile.


What is Legionnaires' disease?

most serious and commonly recognized form of Legionella causing pneumonia (older population).


What is Pontiac fever?

self-limited, flu-like illness without pneumonia affecting the younger population (caused by Legionella.


When does Legionnaires' disease most commonly occur?

late summer/early fall bc it grows in cooling towers/air conditioning units and water supplies or pluming systems.


How does Legionella infect the host?

- it is airborne and will affect the alveolar macrophages in the lungs causing complement binding (allowing more bacteria to enter the cell through these pores) and the cell is resistant to killing once inside the macrophages (by causing a defect in organelle trafficing; dot gene and thu absence of lysosomal fusion).
- the cell inhibits transferrin receptors to try to starve the bacteria from iron availability (which it requires).


**** What are the symptoms and signs of Legionella?

- prodromal phase= resembles influenza
- characteristic feature= HIGH FEVER, BRADYCARDIA, and DIARRHEA.
- altered mental status with normal CSF
- leukocytosis (15,000), hyponatremia, hypophosphatemia


What are the 4 diagnostic methods used to detect Legionella?

1. culture
2. direct fluorescent
3. serology
4. urinary antigen assays
*all are sensitive but not specific


Is mortality high or low in community acquired cases of legionella?

pretty high (greater than 15%), and it is slow to clear with antibiotic treatment (erythromycin, azithromycin, and/or ciprofloxacin used for more than 3 weeks).