Mycoplasma species are unique and widespread bacteria, notable for being among the smallest free-living organisms. They exist in various environments, including as parasites or commensals in humans, animals, and plants. Almost 100 species have been identified, with fifteen known to inhabit humans. These often coexist as normal residents, though some can cause infections.
Unique Characteristics of Mycoplasma
Mycoplasma species have distinct biological features. Their exceptionally small size, typically 0.2 to 0.8 micrometers, positions them among the smallest self-replicating organisms, often compared to large viruses. This diminutive stature is partly due to their remarkably small genome, containing a minimal set of genes necessary for survival and reproduction.
A defining characteristic of mycoplasmas is the complete absence of a rigid cell wall. This lack of a cell wall renders them pleomorphic, meaning they can adopt various shapes, from spherical to filamentous, rather than maintaining a fixed form. Mycoplasmas are also parasitic, often relying on host cells to obtain essential nutrients because they have limited metabolic capabilities for synthesizing their own. They require sterols for growth when cultured in laboratory settings, typically supplied by adding serum to the growth medium.
Common Mycoplasma Infections
Mycoplasma species cause a range of infections, primarily affecting human health. Mycoplasma pneumoniae causes respiratory tract infections, notably “walking pneumonia” or atypical pneumonia. Symptoms often include a dry cough that can persist for weeks, low-grade fever, headache, sore throat, and fatigue, differing from typical bacterial pneumonia. While many Mycoplasma pneumoniae infections are mild, they can also manifest as bronchitis, ear infections (otitis media), and even a version of the common cold.
Genitourinary infections are caused by species such as Mycoplasma genitalium and Ureaplasma urealyticum. These bacteria can be found in the genital tract of healthy, sexually active individuals, but an overgrowth can lead to symptoms. Manifestations in both men and women include painful urination (dysuria), unusual discharge, and pelvic pain. Untreated infections can lead to complications such as chronic prostatitis in men, cervicitis and pelvic inflammatory disease in women, and even infertility or pregnancy complications like preterm labor.
Diagnosis and Treatment Approaches
Diagnosing mycoplasma infections presents challenges due to their unique properties. Traditional bacterial culture methods are often difficult and time-consuming, sometimes taking up to five weeks, due to the organisms’ small size and specific growth requirements. Consequently, diagnosis often relies on molecular tests, such as Polymerase Chain Reaction (PCR), which detects the bacteria’s genetic material, and serological tests that identify antibodies produced by the body in response to the infection. A combination of PCR and serology, particularly IgM antibody detection, is often considered the most effective approach for early and accurate diagnosis, especially in children.
Treatment involves specific antibiotics, as their lack of a cell wall makes them resistant to many common types. Antibiotics that target cell wall synthesis, such as penicillin and other beta-lactams, are ineffective because mycoplasmas do not have this structure. Instead, macrolides (like azithromycin and erythromycin), tetracyclines (such as doxycycline and minocycline), and fluoroquinolones are the primary choices, as they work by inhibiting protein synthesis or DNA replication within the bacterial cell. The increasing prevalence of macrolide-resistant strains of Mycoplasma pneumoniae has led to the use of tetracyclines and fluoroquinolones as second-line treatments, though age-related safety concerns for children exist with these alternatives. Resistance mechanisms in mycoplasmas can involve mutations in ribosomal RNA for macrolides and tetracyclines, and in DNA gyrase or topoisomerase IV for fluoroquinolones.
Preventing Mycoplasma Spread
Preventing mycoplasma spread involves general hygiene and specific precautions based on transmission route. For respiratory species like Mycoplasma pneumoniae, transmission occurs through respiratory droplets released when an infected person coughs or sneezes. Avoiding close contact with symptomatic individuals and practicing good hand hygiene, such as frequent washing with soap and water or using alcohol-based hand sanitizer, can help reduce transmission. Covering the mouth and nose when coughing or sneezing and disposing of used tissues promptly are also recommended.
For sexually transmitted species like Mycoplasma genitalium and Ureaplasma urealyticum, safe sexual practices are important. Consistent and correct use of condoms for all sexual acts significantly reduces the risk of transmission. It is also advisable for individuals experiencing symptoms or after unprotected exposure to get tested, and for all recent sexual partners to be tested and treated concurrently to prevent reinfection. Currently, there is no widely available vaccine for most human mycoplasma species, making preventive measures and prompt treatment even more important.