Mycoplasma pneumoniae

• Mycoplasma pneumoniae is a type of “atypical” bacteria that commonly causes mild infections of the respiratory system.
• In fact, pneumonia caused by M. pneumoniae is sometimes referred to as “walking pneumonia” since symptoms tend to be milder than pneumonia caused by other germs.
• The most common type of illness caused by these bacteria, especially in children, is tracheobronchitis, commonly called a chest cold.
• Symptoms often include being tired and having a sore throat, fever, and cough.
• Sometimes M. pneumoniae can cause pneumonia, a more serious lung infection, which may require care in a hospital.

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Mycoplasma pneumoniae cells attached to ciliated mucosal cells

Pathogenesis

• M. pneumoniae bacteria spread from person-to-person contact by respiratory droplets. and is exclusively a human pathogen.
• M. pneumoniae is primarily an extracellular pathogen that has evolved a specialized attachment organelle for close association with host cells.
• This attachment is critical to the bacteria’s survival and ability to infect. The close association between M. pneumoniae and the host cells prevents the host’s mucociliary clearance mechanisms from removing the bacterium.
• The bacterium attaches to and damages the respiratory epithelial cells at the base of cilia.
• This activates the innate immune response and produces local cytotoxic effects.
• M. pneumoniae 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.
• While M. pneumoniae primarily lives on the surface of the respiratory epithelial cells, it can invade tissues and replicate intracellularly.

The endocytosis of M. pneumoniae by the host cells could:

• Aid in the establishment of a latent or chronic disease state
• Facilitate the bacterium in evading an immune response
• Interfere with the efficacy of certain drug therapies

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Mycoplasma p.

Causes

Mycoplasma pneumoniae are bacteria that can cause illness by damaging the lining of the respiratory system (throat, lungs, windpipe). People can have the bacteria in their nose or throat at one time or another without being ill.

• People spread Mycoplasma pneumoniae bacteria to others by coughing or sneezing.

• When someone infected with M. pneumoniae coughs or sneezes, they create small respiratory droplets that contain the bacteria. Other people can get infected if they breathe in those droplets.

• Most people who spend a short amount of time with someone who is sick with M. pneumoniae do not get infected.
• However, the bacteria often spread between people who live together since they spend a lot of time together.
• M. pneumoniae outbreaks occur mostly in crowded settings like schools, college residence halls, military barracks, nursing homes, and hospitals.
• During school-based outbreaks, if people in the community get sick they are usually family members of ill school children.

Signs and symptoms

In general, infections caused by Mycoplasma pneumoniae are mild. Once someone becomes infected with the bacteria, symptoms usually appear after 1 to 4 weeks.

Symptoms depend on the type of infection. The most common type of infection is tracheobronchitis (chest cold), but pneumonia (lung infection) can occur.

• Common symptoms of a chest cold include:

• Sore throat
• Feeling tired
• Fever
• Slowly worsening cough that can last for weeks or months
• Headache
• Common symptoms of pneumonia include:

• Cough that may produce mucus
• Fever and chills
• Shortness of breath
• Chest pain
• Feeling tired

Children younger than 5 years old could have symptoms that are different from older children, and may have the following cold-like symptoms:

• Sneezing
• Stuffy or runny nose
• Sore throat
• Watery eyes
• Wheezing
• Vomiting
• Diarrhea

Schematic of the phosphorylated proteins in the attachment organelle in Mycoplasma pneumoniae

Diagnosis

Clinical laboratories can provide diagnostic testing for Mycoplasma pneumoniae infections using culture, serology, or nucleic acid amplification methods (see chart below). M. pneumoniae differs from other bacteria in ways that impact the methods used for diagnosis of infection:

• It can pass through filters typically used to remove bacteria.
• Light microscopy cannot detect it.
• It does not produce visible turbidity in liquid growth media. In order to get a visual confirmation of growth, M. pneumoniae cultures requires specialized media.

Currently, there are multiple commercially available kits cleared by the U.S. Food and Drug Administration (FDA) for the detection of M. pneumoniae. Most of these kits are used for detection of multiple respiratory pathogens, including M. pneumoniae.

Treatment

• Most people will recover from an infection caused by Mycoplasma pneumoniae without antibiotics.
• Most Mycoplasma pneumoniae infections are self-limiting; however, clinicians routinely treat pneumonia caused by M. pneumoniae with antibiotics.
• All mycoplasmas lack a cell wall and, therefore, all are inherently resistant to beta-lactam antibiotics (e.g., penicillin).

Clinicians treat the disease with macrolide, tetracycline, or fluoroquinolone classes of antibiotics, taking age of the patient and local antibiotic resistance patterns into consideration:

• Macrolides (e.g., azithromycin): Children and adults
• Fluoroquinolones: Adults
• Tetracyclines (e.g., doxycycline): Older children and adults

Clinicians should not prescribe fluoroquinolones and tetracyclines for young children under normal circumstances. Macrolides are generally considered the treatment of choice. However, clinicians should practice prudent use of macrolide drugs due to the emergence of macrolide-resistant strains of M. pneumoniae.

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Pathogenicity of Mycoplasma pneumoniae in vasculitic-thrombotic disorders

Antibiotic Resistance

Resistance to macrolides has been emerging in M. pneumoniae since the 2000s. This issue is especially troubling in Asia, where resistance rates have been as high as 90%. The United States and Europe have also reported macrolide resistance. Current data suggest that the prevalence of macrolide resistance in M. pneumoniae may be around 10% in the United States, with regional variability.

• Studies have reported that patients with infections due to macrolide-resistant strains may have fever and cough for a longer duration than patients infected with macrolide-sensitive strains.
• Experts need to learn more about the extent of macrolide resistance and its clinical implications to inform prescribing decisions.

Complications

While M. pneumoniae usually cause mild infections, severe complications can occur that require care in a hospital. M. pneumoniae infections can cause or worsen the following complications:

• Serious pneumonia
• Asthma attacks or new asthma symptoms
• Encephalitis (swelling of the brain)
• Hemolytic anemia (too few red blood cells, which means fewer cells to deliver oxygen in the body)
• Renal dysfunction (kidney problems)
• Skin disorders like Stevens-Johnson syndrome, erythema multiforme, toxic epidermal necrolysis

Risk factors

Mycoplasma pneumoniae infections are most common in young adults and school-aged children, but can affect anyone. People living and working in crowded settings are at increased risk. These settings include:

• Schools
• College residence halls
• Military barracks
• Nursing homes
• Hospitals
• Other people at increased risk for serious infections include those:

• Recovering from a respiratory illness
• With a weakened immune system

Prevention

• People can get infected with Mycoplasma pneumoniae more than once. While there is no vaccine to prevent M. pneumoniae infections, there are things people can do to protect themselves and others.

• Good Hygiene
• Like many respiratory germs, Mycoplasma pneumoniae most commonly spread by coughing and sneezing. Some tips to prevent the spread of M. pneumoniae include:

• Cover your mouth and nose with a tissue when you cough or sneeze.
• Put your used tissue in a waste basket.
• If you don’t have a tissue, cough or sneeze into your upper sleeve or elbow, not your hands.
• Wash your hands often with soap and water for at least 20 seconds.
• If soap and water are not available, use an alcohol-based hand rub.
• Preventive Antibiotics
• Doctors generally do not prescribe antibiotics to help prevent someone else from getting sick (for example, a close contact of an infected person).

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