Mycoplasma hominis is a microscopic organism classified as a bacterium that frequently colonizes the human urogenital tract. This organism is unique among bacteria because it lacks a rigid cell wall, which makes it structurally distinct from many other pathogens. Due to this missing structure, it is often grouped with other organisms known as mollicutes, which are some of the smallest free-living organisms known. While the organism is commonly found in sexually active individuals, its presence does not automatically indicate an active infection or disease state.
Classification and Transmission of Mycoplasma Hominis
The question of whether Mycoplasma hominis is a sexually transmitted disease (STD) has a complex answer rooted in its biology and behavior. The bacterium is primarily spread through sexual contact, including vaginal, oral, and anal intercourse, which functionally places it within the category of sexually transmitted infections. However, it is not always classified alongside traditional STDs because it can also exist naturally as a commensal, or part of the normal flora, in the genitourinary tract of many healthy, asymptomatic individuals.
The likelihood of being colonized by M. hominis directly correlates with the number of lifetime sexual partners, which strongly supports its primary route of transmission being sexual contact. It is considered an opportunistic pathogen, meaning it typically only causes disease when the natural microbial balance is disrupted or when the host’s immune system is weakened.
Beyond sexual transmission, M. hominis can also be passed vertically from a pregnant person to their baby during childbirth. This vertical transmission occurs when the newborn passes through the colonized birth canal, posing a risk of infection to the infant, particularly those born prematurely.
Identifying Symptoms and Associated Health Risks
Many people who carry Mycoplasma hominis remain completely asymptomatic, meaning they experience no noticeable symptoms despite being colonized. When the organism overgrows and causes an active infection, the signs and symptoms are often non-specific and can be mistaken for other sexually transmitted infections. The health risks vary significantly depending on the person’s sex and overall health status.
In women, M. hominis is associated with several serious gynecological conditions. It is frequently recovered in cases of Pelvic Inflammatory Disease (PID), an infection of the upper reproductive organs that can lead to long-term issues like chronic pelvic pain and ectopic pregnancy. The bacterium is also often found in higher quantities when bacterial vaginosis (BV) is present.
For pregnant individuals, the infection carries the risk of adverse pregnancy outcomes, including chorioamnionitis, postpartum fever, preterm labor, or miscarriage. In men, an active M. hominis infection can manifest as urethritis (inflammation of the urethra), leading to symptoms like a burning sensation during urination or a discharge from the penis.
Less common, more invasive infections include epididymitis (inflammation of the coiled tube at the back of the testicle) or prostatitis. Newborns who acquire the organism through vertical transmission are susceptible to infections, especially if they are born preterm. Potential complications in neonates include:
- Respiratory problems
- Sepsis
- Severe central nervous system issues like meningitis
In all populations, particularly those with compromised immune systems, M. hominis can cause systemic infections, including:
- Surgical wound infections
- Joint inflammation (septic arthritis)
- Blood infections (bacteremia)
Diagnosis and Effective Treatment Strategies
Diagnosis of an active M. hominis infection is typically not performed unless a person is symptomatic or has a condition highly associated with the bacterium, such as PID. Traditional culturing methods can be challenging because the organism is slow-growing and requires specialized media. The most sensitive and specific method for detection is the use of nucleic acid amplification tests (NAATs), such as Polymerase Chain Reaction (PCR) testing, which detects the bacterium’s genetic material. These tests are usually performed on swab samples collected from the urethra or cervix, or from a urine sample.
The lack of a cell wall in M. hominis dictates the treatment strategy. This structural absence makes the organism naturally resistant to common antibiotics like penicillin and cephalosporins that target cell wall synthesis.
The first-line treatment for M. hominis infections is generally an antibiotic from the tetracycline class, such as doxycycline. This medication is typically prescribed for seven to fourteen days, depending on the severity and location of the infection. Alternative treatments include fluoroquinolones, such as moxifloxacin, which may be used in cases of tetracycline resistance or for invasive infections. For pregnant individuals, clindamycin is often considered a safer alternative, as tetracyclines are generally avoided during pregnancy. Because M. hominis is sexually transmitted, the treatment plan often includes testing and, if necessary, treating all sexual partners to prevent the cycle of reinfection.