Mycoplasma pneumoniae

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Mycoplasma pneumoniae


Introduction to bacteria

Bacterial structure and functions


Mycoplasma pneumoniae


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USMLE® Step 1 questions

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High Yield Notes

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Mycoplasma pneumoniae

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USMLE® Step 1 style questions USMLE

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A 24-year-old man comes to the clinic because of a 2-week history of nonproductive cough and intermittent headaches. The patient has been feeling severely fatigued for the past few weeks, even though his daily regimen has remained the same. He is currently training to become an artillery officer and lives in army barracks. Past medical history is noncontributory, and he takes a multivitamin daily. He does not use tobacco, alcohol, or illicit substances. Temperature is 38.2°C (100.8°F), pulse is 96/min, and blood pressure is 128/85 mmHg. Physical examination reveals conjunctival pallor and pale mucous membranes. Bilateral crackles are heard on chest auscultation. Chest radiograph reveals diffuse bilateral infiltrates. Laboratory results are as follows:

Laboratory value  Result 
Complete blood count 
Hemoglobin   9.6 g/dL 
 Hematocrit  30% 
 Leukocyte count  9,100/mm3 
 Platelet count  250,000/mm3 
 MCV  88 µm3 
 Haptoglobin  23 mg/dL (N= 41-165 mg/dL) 

 Further testing in this patient is likely to reveal which of the following findings?  

External References

First Aid









Mycoplasma pneumoniae p. , 148

Eaton agar

Mycoplasma pneumoniae p. , 148

Fluoroquinolones p. 36

Mycoplasma pneumoniae p. , 148

Headache p. 536

Mycoplasma pneumoniae p. , 148

Macrolides p. 190

Mycoplasma pneumoniae p. , 148

Mycoplasma pneumoniae p. , 148

anemia and p. 417

erythema multiforme p. 494

tetracyclines p. 189

Pneumonia p. 707

Mycoplasma pneumoniae p. , 148


Mycoplasma pneumoniae is a small bacterium which causes atypical pneumonia in young adults.

Mycoplasma, as a genus, have a cell membrane that is packed with sterols, but they lack a proper, rigid cell wall.

Therefore, they don’t take up dye under Gram staining, so they can’t be visualized with light microscopy.

Additionally, they are highly pleomorphic bacteria, meaning they have no fixed shape and size, and they’re also osmotically unstable in the external environment.

So, to survive, Mycoplasmas invade host cells and live intracellularly.

Now, Mycoplasma pneumoniae is a facultative anaerobe, meaning it can live without oxygen if it has to, but it grows better in an aerobic environment.

So it prefers places like lungs or respiratory airways, where there is an unlimited flow of oxygen.

As a result, some people may carry this bacteria in their nose or throat, and when they sneeze or cough, these organisms get out in the form of small respiratory droplets.

And when other people inhale these droplets, they may get infected, especially when they spend a lot of time together in close quarters.

So Mycoplasma pneumoniae infections occur mostly in children who go to school, young adults in college, or military recruits.

Following inhalation of the pathogen droplets, Mycoplasma pneumoniae attaches to an epithelial cell in the respiratory tract, using a specialized attachment organelle which has an adhesive protein complex, called ‘adhesion protein P1’ at its tip.

Adhesion protein P1 attaches to the host cell surface, like the respiratory epithelial cell, and holds on for dear life.

This makes it much harder for the mucociliary clearance mechanisms, which normally remove any foreign pathogen out of the respiratory tract, to clear the bacteria.

So Mycoplasma pneumoniae multiplies and damages the respiratory epithelial cells in the process.

When they reach the lungs, this starts a local inflammatory response, and lung tissue fills with white blood cells, proteins, fluid, and even red blood cells if a nearby capillary gets damaged in the process - leading to a local cytotoxic effect.

So Mycoplasma pneumoniae avoid the battlefield by sneaking inside lung cells, where they remain dormant or replicate intracellularly.


Mycoplasma pneumoniae is a type of bacteria that causes a type of pneumonia known as "walking pneumonia", because affected people may not feel very sick, as opposed to typical pneumonia. Mycoplasma pneumonia presents with milder symptoms, such as gradual onset of symptoms such as fever, cough, sore throat, and fatigue.


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