Mycoplasma are a unique group of bacteria known for their exceptionally small size and lack of a rigid cell wall. This characteristic significantly influences their behavior and interaction within various environments. Found in diverse habitats, certain species cause a range of infections in humans. Understanding their fundamental differences from typical bacteria is important for comprehending the diseases they cause and how they are managed.
Unique Characteristics of Mycoplasma
Mycoplasma are the smallest known self-replicating bacteria, typically 0.1 to 0.5 micrometers in diameter. Their diminutive size allows them to pass through many conventional bacterial filters, earning them the designation of “filterable” bacteria. This also means they cannot be readily observed using standard light microscopy.
A defining feature of Mycoplasma is the complete absence of a peptidoglycan cell wall. This lack of a rigid outer layer makes Mycoplasma highly pleomorphic, allowing them to assume various shapes. To compensate, their cell membranes are unusually tough and contain sterols, providing structural stability. This unique membrane composition makes them vulnerable to changes in osmotic pressure. Mycoplasma also possess remarkably small genomes, reflecting their reliance on host cells for many essential nutrients.
Mycoplasma and Human Health
Mycoplasma species can cause a variety of infections in humans, affecting different body systems. Mycoplasma pneumoniae is a well-known cause of respiratory tract infections, particularly “walking pneumonia” or atypical pneumonia. This condition often presents with milder symptoms than typical bacterial pneumonia, including a dry cough, headache, fatigue, fever, and mild shortness of breath. Transmission occurs through respiratory droplets, and symptoms typically appear one to four weeks after exposure, potentially lasting for several weeks.
Beyond respiratory issues, Mycoplasma pneumoniae can sometimes lead to more severe complications, such as asthma attacks, inflammation of the brain (encephalitis), or a type of anemia (hemolytic anemia). Other Mycoplasma species are primarily associated with urogenital infections. Mycoplasma genitalium is a sexually transmitted infection (STI) that can cause symptoms similar to other STIs, including discharge from the penis or vagina, and painful urination. Many individuals infected with Mycoplasma genitalium may not experience any symptoms, making detection and treatment challenging.
Untreated Mycoplasma genitalium infections can lead to complications such as urethritis in men and cervicitis or pelvic inflammatory disease (PID) in women, which can potentially impact fertility. Ureaplasma urealyticum and Mycoplasma hominis are other species found in the urogenital tract. While they can be part of the normal flora, their overgrowth can cause urethritis, bacterial vaginosis, cervicitis, or PID, and have been linked to complications in newborns. Symptoms for these urogenital infections often include painful urination, unusual discharge, and lower abdominal pain.
Diagnosing and Treating Mycoplasma Infections
Diagnosing Mycoplasma infections presents challenges due to their small size, unique characteristics, and often non-specific symptoms. Healthcare providers use various laboratory tests to confirm an infection. Polymerase chain reaction (PCR) tests, which detect the bacteria’s genetic material, are highly sensitive and specific, often serving as the gold standard. Serology tests, measuring antibodies, can also be used, though results may be slower or lead to false positives. While bacterial culture can identify Mycoplasma, it is time-consuming and difficult due to their fastidious growth requirements.
The absence of a cell wall in Mycoplasma has significant implications for treatment. Many common antibiotics, such as penicillin and other beta-lactams, target the bacterial cell wall. Since Mycoplasma lack this structure, these antibiotics are ineffective. Instead, treatment involves antibiotics that act through different mechanisms, such as inhibiting protein synthesis or DNA replication.
Macrolide antibiotics, including azithromycin, clarithromycin, and erythromycin, are frequently used as first-line treatments, particularly for respiratory ones. Tetracyclines, such as doxycycline and minocycline, are effective alternatives. Fluoroquinolones like levofloxacin and moxifloxacin may be prescribed if macrolides are ineffective or for specific situations.
Treatment courses usually last 7 to 14 days, though longer durations may be necessary. Completing the full course of antibiotics is important to ensure eradication and minimize antibiotic resistance. Resistance to these specific antibiotic classes has been observed in some Mycoplasma strains, highlighting the need for careful monitoring and appropriate treatment selection.