Mycoplasma hominis is a microscopic bacterium commonly found in the lower genitourinary tract of sexually active adults. While it often exists harmlessly as a commensal organism, it can become an opportunistic pathogen under certain conditions. This can lead to various inflammatory infections, particularly within the reproductive and urinary systems.
Unique Characteristics of the Bacterium
The most defining feature of Mycoplasma hominis is its complete lack of a peptidoglycan cell wall, a rigid outer layer present in almost all other bacteria. Because it lacks this protective layer, the bacterium is bounded only by a three-layered membrane that contains sterols, which it must acquire from its host environment to maintain structural integrity.
This unique biological structure has significant implications for infection management. Many common antibiotics, such as penicillins and cephalosporins, function by targeting and destroying the cell wall. Since M. hominis does not have this structure, it is innately resistant to these classes of drugs. This inherent resistance necessitates a different approach to antimicrobial therapy.
How the Infection Spreads
The primary method of transmission for Mycoplasma hominis among adults is through sexual contact, often leading to its classification as a sexually transmitted infection. Transmission can occur through unprotected vaginal, oral, or anal intercourse. The risk of colonization increases directly with the number of lifetime sexual partners.
A secondary, but clinically important, transmission route is vertical transmission from a colonized mother to her newborn during birth. While colonization in neonates is common after a vaginal delivery, it is often transient, though it can lead to serious complications in some cases, particularly in premature infants.
Common Symptoms and Associated Health Conditions
For the majority of individuals colonized with Mycoplasma hominis, the bacterium causes no noticeable symptoms. However, when the organism overgrows or spreads beyond the lower tract, it can be linked to several inflammatory conditions in both men and women.
In women, M. hominis is frequently associated with Pelvic Inflammatory Disease (PID), which is an infection of the upper reproductive organs. PID can result in severe long-term consequences, such as chronic pelvic pain, infertility, and an increased risk of ectopic pregnancy. The bacterium has also been implicated in bacterial vaginosis and postpartum fever.
Men who become symptomatic may experience Non-Gonococcal Urethritis (NGU), which is an inflammation of the urethra. Symptoms can include a burning sensation or pain during urination, and a discharge from the penis that may be clear or milky. In rarer instances, the infection can progress to the epididymis or prostate gland, causing epididymitis or prostatitis.
In newborns who acquire the infection vertically, or in adults who are immunocompromised, M. hominis can cause severe, extragenital infections. These can include respiratory issues like pneumonia, or meningitis, an infection of the membranes surrounding the brain and spinal cord. In individuals with suppressed immune systems, the bacterium has also been linked to joint infections, wound infections, and bacteremia.
Testing and Treatment Protocols
Diagnosis relies on laboratory testing of clinical samples, typically fluid swabs from the urethra, cervix, or vagina, or a urine sample. The preferred method is the Nucleic Acid Amplification Test (NAAT), which detects the organism’s genetic material. While traditional bacterial culture can be performed, NAAT is often favored because M. hominis is slow-growing and difficult to cultivate.
First-line medication typically involves antibiotics from the tetracycline class, specifically doxycycline, which works by inhibiting protein synthesis within the bacterial cell. Doxycycline is commonly prescribed for a period of seven to fourteen days.
When tetracyclines are contraindicated (e.g., during pregnancy) or resistance is detected, alternative antibiotics are considered. Clindamycin is an established alternative for certain extragenital infections. Josamycin, a specialized macrolide, may be used in pregnant women, as most other macrolides like azithromycin are ineffective against M. hominis. Resistance to tetracycline is a growing concern that complicates treatment.