Mycoplasma Flashcards
which 4 mycoplasma are definitively associated with human disease?
- Mycoplasma pneumoniae —> upper respiratory infection, bronchitis, pneumonia
cause STDs:
2. Ureaplasma urealyticum
3. Mycoplasma hominis
4. Mycoplasma genitalium
what kind of diseases to Ureaplasma urealyticum, Mycoplasma hominis, and Mycoplasma genitalium produce in men and women, respectively?
all cause STDs
men - nongonococcal urethritis
women - vaginosis, cervicitis, pelvic inflammatory disease (PID)
[the other relevant Mycoplasma is Mycoplasma pneumoniae —> respiratory infections]
what shape are Mycoplasma?
smallest free-living organism by size and genome that can be cultured
highly polymorphic bc they LACK rigid cell wall (NO peptidoglycan)
have 3-layer membrane instead
what is the clinical significance of the fact that mycoplasmas lack a rigid cell wall (and therefore peptidoglycan), but instead have a 3-layer membrane?
[how does this effect labs and treatment]
completely resistant to penicillins and other antibiotics that target cell wall
not visible by gram staining
major antigenic determinants are instead membrane glycolipids and proteins —> antibiotics to mycoplasmas cross-react with human RBC
what are the growth requirements of mycoplasmas?
fastidious organisms
require exogenous sterols for membrane (cholesterol added to medium)
very slow growing!
what do mycoplasmas have in their membranes that is not present in other bacteria or viruses?
sterol-containing membranes - require cholesterol source to be cultured in medium
describe the type of pneumonia caused by Mycoplasma pneumoniae
atypical (walking) pneumonia:
- transmitted via respiratory secretions
- prominent causative agent of pneumonia in closed populations (military, college, etc)
- respiratory pathogenicity linked to high affinity of bacteria for respiratory epithelial cells
how would a mutation in an adhesin (such as P1, P30, P65, or P116) affect the pathogenicity of Mycoplasma pneumoniae?
would cause it to be avirulent because its respiratory pathogenicity is liked to high affinity for binding respiratory epithelial cells
attachment occurs at base of cilia between adhesins of bacteria and glycoprotein of epithelial cell —> causes loss of cilia and sloughing of cell into lumen —> hallmark cough
how does the incubation period of atypical pneumonia caused by Mycoplasma pneumoniae compare to that caused by viral respiratory infections?
atypical pneumonia: 2-3 week incubation period, gradual (several days) onset of symptoms (hallmark cough)
viral respiratory infection: 1-3 days incubation period
how does Mycoplasma pneumoniae typically infect children under 3, patients 5-20, and adults over 20, respectively?
under 3 years: primarily upper respiratory infection
5-20 years: bronchitis, pneumonia (highest attack rate in this group)
20+ years: pneumonia
describe the methodology behind the cold agglutinin test for Mycoplasma pneumoniae (and why this works)
major antigenic determinants are membrane glycolipids and proteins that can cause antibody cross-reaction to human RBCs
infection leads to formation of cold agglutinins (IgM antibodies against altered oligosaccharide surface antigen on RBCs)
test: chill patient blood and see if tube becomes coated with RBC’s (this can be reversed if tube is warmed)
patients with sickle cell or related diseases are at risk for higher disease severity caused by Mycoplasma pneumoniae - what would be a key PE finding of this severity?
can develop extremely high titers of cold agglutinins (due to antibody against bacterial membrane cross reacting with RBCs)
this can lead to digital necrosis
why is it hard to test for infection by Mycoplasma pneumoniae? how is diagnosis typically made (when it is made)?
mostly undiagnosed because:
- culturing takes up to 2 weeks
- cold agglutination test is not specific or sensitive enough
- long incubation period makes serological tests negative early on
- PCR tests not commercially available
if diagnosis is made, based on clinical recognition of gradual onset of symptoms and family outbreak characteristics (due to long incubation periods)
how are undiagnosed cases of Mycoplasma pneumoniae usually treated, and why might this be ineffective?
patients presenting with pneumonia often given standard therapy for community acquired pneumonia (CAP)
however beta-lactam antibiotics are sometimes used, which would be ineffective against Mycoplasma pneumoniae, since it lacks a cell wall and peptidoglycan
