MYCOPLASMA

Mycoplasma

Mycoplasma is a genus of bacteria characterized by the absence of a cell wall, which makes them unique among prokaryotes. The most clinically significant species is Mycoplasma pneumoniae, known for causing atypical pneumonia, often referred to as "walking pneumonia." Mycoplasma species are among the smallest free-living organisms and are capable of causing a range of respiratory, urogenital, and systemic infections.

Microscopic Appearance

• Lack of Cell Wall:

  • Unlike most bacteria, Mycoplasma species do not have a peptidoglycan cell wall, making them resistant to antibiotics that target cell wall synthesis (e.g., beta-lactams).

• Shape:

  • Pleomorphic, meaning they can vary in shape due to the absence of a rigid cell wall.

  • Typically, they appear as very small, flexible, and variable shapes, including round or filamentous forms.

• Size:

  • Extremely small, with diameters ranging from 0.2 to 0.3 micrometers.

• Staining:

  • Not visible on Gram staining due to the lack of a cell wall. They are often identified using specialized media and diagnostic techniques.

• Mycoplasma generally grow more slowly than bacteria.

• They are usually resistant to antibiotics like penicillin,

• cephaloridine, vancomycin etc. which action cell wall.

• They are sensitive to tetracycline.

• They are also killed by temperature of 40 55 C in fifteen minutes.

• They do not produce spores.

• Generally, mycoplasmas are facultative anaerobes, except for Mycoplasma pneumoniae which is a strict aerobe

Examples of Mycoplasma

• Mycoplasma pneumoniae

• Mycoplasma hominis

• Mycoplasma genitalium

• Ureaplasma urealyticum

Virulence Factors

• Adhesins:

  • Mycoplasma pneumoniae has a specialized structure known as the P1 adhesin that facilitates attachment to the respiratory epithelium, particularly the ciliated epithelial cells, allowing colonization and persistence in the host.

• Production of Hydrogen Peroxide:

  • Contributes to tissue damage and inflammation by inducing oxidative stress in host cells.

• Superantigen Activity:

  • Some Mycoplasma species can stimulate an exaggerated immune response by acting as superantigens, leading to excessive cytokine release and immune-mediated damage.

• Immune Evasion:

  • Mycoplasma can alter its surface proteins to evade the host immune system, contributing to chronic infections.

Pathogenesis

• Attachment and Colonization:

  • Mycoplasma pneumoniae attaches to the ciliated epithelial cells of the respiratory tract using P1 adhesin. This disrupts normal ciliary function, leading to impaired mucus clearance and a persistent cough.

• Inflammation:

  • The bacteria induce an immune response characterized by local inflammation, which can lead to tissue damage. The production of hydrogen peroxide exacerbates this process by causing oxidative damage to host tissues.

• Immune Response:

  • The host's immune response to the bacteria can result in symptoms such as fever, malaise, and cough. The lack of a cell wall also allows Mycoplasma to persist in the host, leading to prolonged infection.

Clinical Manifestations

• Respiratory Infections:

  • Atypical Pneumonia (Walking Pneumonia):

    • Gradual onset of symptoms including a dry, persistent cough, low-grade fever, malaise, and headache.

    • The cough is often non-productive, and the illness is usually mild but can become more severe in some cases, particularly in older adults or those with underlying health conditions.

  • Tracheobronchitis:

    • Inflammation of the trachea and bronchi, leading to symptoms such as sore throat, hoarseness, and a persistent, dry cough.

• Extrapulmonary Manifestations:

  • Dermatologic:

    • Skin rashes, including erythema multiforme and Stevens-Johnson syndrome.

  • Cardiac:

    • Myocarditis or pericarditis in rare cases.

  • Neurological:

    • Encephalitis, meningitis, or transverse myelitis, though these are rare complications.

  • Hematologic:

    • Hemolytic anemia due to cold agglutinins (IgM antibodies that agglutinate red blood cells at low temperatures).

Lab Diagnosis

• Culture:

  • Mycoplasma pneumoniae is difficult to culture because of its slow growth and fastidious nature. Specialized media such as SP4 broth can be used, but cultures may take weeks and are not commonly performed in clinical settings.

• Serology:

  • Detection of specific antibodies (IgM and IgG) against Mycoplasma antigens is commonly used. Cold agglutinin titers may also be elevated in cases of M. pneumoniae infection.

  • It include CFT(The complement fixation test )is an immunological medical test that can be used to detect the presence of either specific antibody or specific antigen in a patient's serum, based on whether complement fixation occurs) and ELISA.

• PCR:

  • Polymerase chain reaction (PCR) is a highly sensitive and specific method for detecting Mycoplasma pneumoniae DNA in respiratory samples, making it a preferred diagnostic tool.

• Chest X-ray:

  • May show patchy or diffuse infiltrates, often out of proportion to physical findings in cases of atypical pneumonia.

Treatment

• Antibiotics:

  • Because Mycoplasma species lack a cell wall, they are inherently resistant to beta-lactam antibiotics like penicillins and cephalosporins.

  • Macrolides (e.g., azithromycin, clarithromycin):

    • First-line treatment, especially in children and pregnant women.

  • Tetracyclines (e.g., doxycycline):

    • An alternative, particularly in adults.

  • Fluoroquinolones (e.g., levofloxacin):

    • Another alternative, particularly in adults, but generally avoided in children due to potential side effects.

  • Tetracycline and erythromycin are the antibiotics of choice.

• Supportive Care:

  • Most cases of Mycoplasma infections are self-limiting, so treatment primarily focuses on symptom relief, including the use of antipyretics and hydration.

• Prevention:

  • No vaccine is currently available for Mycoplasma pneumoniae.

  • Preventive measures include good hygiene practices, particularly in crowded settings like schools and military barracks, to reduce the spread of respiratory infections.