1.
Structure
a.
Mycoplasma
pneumoniae lacks a cell wall (and thus a periplasmic space). Contains
sterols in their cell membrane for structural support.
b.
Extremely small and elongated, requiring a
stereomicroscope for viewing morphology.
2.
Pathobiology:
a.
They have an extracellular capsule that helps
them adhere to host cells
b.
Obligate aerobe (different from other Mycoplasma
which are facultative)
c.
Antigenic components are present in the
cell membrane (glycolipids, proteins); an adhesin molecule, PI adhesin, helps M.
pneumoniae adhere to respiratory epithelium
d.
Adherence to respiratory epithelium can
destroy cilia and disrupt normal clearance of upper-respiratory tract, allowing
microbes to reach the lower respiratory tract which then stimulates an
inflammatory response, causing the persistent cough
e.
Produces a unique virulence factor known as
Community Acquired Respiratory Distress Syndrome (CARDS) toxin. The CARDS toxin
most likely aids in the colonization and pathogenic pathways of M. pneumoniae, leading to inflammation and airway
dysfunction
3.
Epidemiology
a.
Strict human pathogen spread by close
contact; not seasonal; targets school age children and young adults
4.
Laboratory
diagnosis
a.
Often difficult to test and rely more
on clinical assessment; Culture is slow; Commonly used test is cold agglutinin
antibody assay but this is not very sensitive
b.
Has no cell wall and presents with a
fried-egg appearance after a 2-3 week culture on an Eaton agar
5.
Disease
manifestations
a.
Asymptomatic carriage;
tracheobronchitis; mild form of "atypical" pneumonia in young people
(shortness of breath, cough, not much infiltrate on X-ray)
b.
Treat with erythromycin or
tetracycline
c.
Coined “walking pneumonia” due to
resistance to beta-lactam antibiotics like penicillin
i.
Also resistant to glycopeptides,
sulfonamides, trimethoprim, polymixins, nalidixic acid, rifampin
d. Lack of cell wall makes it very
susceptible to dessication
e.
Prevention and control
i.
Difficult -- vaccines ineffective;
difficult to isolate patients because they are often infectious for prolonged
period
f.
Delayed onset of symptoms and similarity of
symptoms to other pulmonary conditions make it hard to clinically diagnose
i.
Atypical pneumonia due to Legionella is usually in older patients and the immune-compromised
and is visualized with silver stain
ii.
Atypical pneumonia due to Chlamydia-related bacteria is usually more mild and is visualized
with a Giemsa stain