Mycoplasma pneumoniae causes Mycoplasma pneumonia which is probably the easiest disease-agent association I’ve ever seen. Mycoplasma pneumoniae is a super cool organism. It doesn’t have any peptidoglycan, so it doesn’t have a bacterial cell wall at all. To help with it’s integrity, it has a three-layer thick cell membrane made of sterols.
Mycoplasma pneumonia is an atypical pneumonia. Atypical pneuomonias are called this because they have a very long onset and duration, but relatively milder symptoms. The symptoms are usually more systemic than respiratory and include fever, malaise. And also have weird findings like there’s a dry cough but no sputum production, and normal white blood cell numbers.
When these patients have a chest radiograph, there’s no lobar consolidation. The infiltrates are diffuse, and so severe you expect the patient to be worse off than they are. but they’re just up and walking around! That’s why atypical pneumonia is called walking pneumonia.
It can cause the development of erythema multiforme which is a Type-IV hypersensitivity that causes an eruption of small target-like rashes over the extensor surfaces, which will typically resolve in a few days.
It can very rarely cause the formation of Steven-Johnson syndrome which is a spectrum of skin lesions from red macules to fluid-filled bullae.
Since this organism doesn’t have cell wall, Gram-staining is not helpful. Culture requires the use of Eaton’s agar, but takes weeks to produce so it isn’t used often. Diagnosis is usually through detecting anti-Mycoplasma pneumoniae antibodies or through detecting cold agglutinins.
This really weird thing happens sometimes. When you take a patient’s blood in an anticoagulation tube, it’s not suppose to coagulate at all. But sometimes, if you put the tube in a fridge the blood will coagulate. This is when you have cold agglutinins. During some infections, IgM molecules are created against the RBC I-antigen. Due to chemistry and physics non-sense the antibodies binds better to the RBCs when the temperature is around 4C. (Which is refrigeration temperature). This binding to RBCs will cause the lysis of those RBCs causing a hemolytic anemia, causing weakness, dizziness, dyspnea, jaundice, dark-colored urine, hepatosplenomegaly, etc.
This infection is often self-limiting but if treatment is needed, it’s important to remember that this organism doesn’t have a cell wall, so any drugs that target the formation of the peptidoglycan layer are not useful. Tetracycline and Erythromycin are effective.
A 25-year-old female presents to the clinic with progressively worsening shortness of breath for the past three weeks. Vital signs reveal a temperature of 100F, a pulse of 110 beats/min, and an oxygen saturation of 93% on room air. Physical examination reveals mild erythema of the nasal mucosa, and inspiratory rales at the right lung base. He is producing a very small amount of sputum that is not red. His purified protein derivative test was negative. Chest radiography reveals diffuse, bilateral, mutli-lobe infiltrates. What is the fastest method to confirm the most likely diagnosis?
A. Cold agglutinin test
B. Urine antigen test
C. Acid-fast staining
D. Growth on Eaton’s Agar
First, diagnose the patient
This patient is presenting with fever, tachycardia, dyspnea, rales, and shortness of breath for the past 3 weeks, which is a long duration for a respiratory infection. He is also only producing a small amount of sputum. Therefore this is highly suggestive of an atypical pneumonia.
Atypical pneumonia can be caused by Mycoplasma pneumoniae, Chlamydia pneumoniae, Chlamydia psittaci, and Legionella pneumophila.
Chlamydia spp. infections have to be diagnosed via serology. Legionella pneumophila will be diagnosed via growth on Buffered Charcoal Yeast Extract agar or via urine antigen testing.
A. Cold agglutinin test is a really fast way to test for Mycoplasma pneumoniae infections because 50-70% of patients will form IgM antibodies against the RBC I antigen, which causes blood coagulation at cold temperatures.
B. Urine antigen testing would be appropriate and fast if the patient had Legionnaire’s Disease or Pontiac Fever, however this patient isn’t presenting with pneumonia and diarrhea which would suggest Legionnaire’s Disease or a mild, flu-like illness that would possibly be Pontiac Fever. Therefore this isn’t a good test for the most likely diagnosis.
C. Acid-fast staining is great to diagnose Mycobacterium spp. infections. This isn’t a tuberculosis infection because this patient is not presenting with consolidations in the upper lobes with hilar adenopathy. The patient also had a negative PPD test.
D. Growth on Eaton’s agar would confirm an infection with Mycoplasma pneumoniae but this takes weeks to accomplish.
Therefore,
References:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5475226/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5475226/
The Bradley Lab 
nice
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good written
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