Mycoplasma pneumoniae

Mycoplasma pneumoniae


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much more. Try it free today! 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 a 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. As a result, individuals infected by Mycoplasma
pneumoniae are often asymptomatic or may have nonspecific symptoms like fatigue, sore throat,
mild fever and dry hacking cough – all of which aren’t typical of bacterial pneumonia
– hence the name atypical pneumonia. Besides, the person may not feel very sick,
as opposed to a person suffering from other bacterial pneumonia – where they’ll be surely
bedridden and suffering from more severe symptoms like dyspnea, or shortness of breath, fever,
chest pain, and a productive cough. This is why, sometimes a case of atypical
pneumonia is also referred to as walking pneumonia. Mycoplasma pneumoniae can also cause encephalitis,
especially following atypical pneumonia in children. Symptoms of encephalitis include fever, changes
in mental status, and neck stiffness. Diagnosing a Mycoplasma pneumoniae infection
requires a chest X-ray – which reveals a patchy infiltrate, that denotes severe infection. Quite the discrepancy for something called
walking pneumonia! For example, here is how a normal lung looks
like, and in comparison, this is how a Mycoplasma pneumoniae infected lung looks like. Besides imaging, diagnosis can also be made
by getting a sputum sample and growing the organism on Eaton’s agar media, which is
rich in cholesterol and nucleic acids. Growth takes about 2 to 3 weeks, and Mycoplasma
pneumoniae forms ‘dome-shaped colonies’, which look like fried-eggs. But this takes a long time, so growing the
bacteria is not commonly done. Instead, a cold agglutinin test is usually
performed, which is based on the fact that certain antigens of human red blood cells
and antigens of mycoplasma cell membrane are quite similar. As a result, at 4 degrees celsius, IgM antibodies
against bacterial antigens cross-react with human RBC antigens and make them agglutinate,
or clot. Using this basic principle, a simple bedside
test can be done, where the patient’s blood is taken in a tube and placed in a box of
ice. If they have IgM antibodies against Mycoplasma
pneumoniae, the blood clumps and the test is positive. However, these antibodies take time to develop,
so a negative test doesn’t necessarily rule out the infection. When encephalitis is suspected, a lumbar puncture
and cerebrospinal fluid analysis are also done. Ok, now, atypical pneumonia is generally self-limiting. But, if it doesn’t resolve on its own, antibiotics
are needed. And since mycoplasmas don’t have a cell
wall, cell wall inhibitors like beta-lactam antibiotics are inefficient So treatment relies
on antibiotics that inhibit protein biosynthesis, like tetracyclines, or macrolides like erythromycin
and azithromycin. All right, as a quick recap, Mycoplasma pneumoniae
is a small bacterium that causes atypical pneumonia in young adults and military recruits. Diagnosis of atypical pneumonia relies can
be based on a chest X-ray, which reveals patchy infiltrates, or on a positive cold-agglutinin
test where clumping of RBC occurs at 4 degrees celsius. Mycoplasma pneumoniae can also be grown on
Eaton’s agar, forming fried-egg colonies, but this takes 2-3 weeks. If the disease doesn’t resolve on its own,
tetracyclines and macrolides like erythromycin, azithromycin are used to treat the infection.

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