Mycoplasma pneumoniae - MegaMicro

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Mycoplasma pneumoniae

Micro > Bacteriology > Mycoplasma and Ureaplasma
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
Related concepts

1.       Atypical Pneumonia
2.       Tracheobronchitis
3.       Obligate aerobe
4.       Fried-egg culture
5.       CARDS toxin

Fried Egg appearance (source: Source: http://www.sigmaaldrich.com/technical-documents/protocols/biology/testing-for-mycoplasma.html)
 
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