Mycoplasma hominis bloodstream infection following transfemoral cannulation for extracorporeal life support: a case report

In the human body, certain microscopic organisms live quietly in the genital and urinary areas without causing trouble. These are known as commensals, essentially harmless residents that coexist with us. However, when the body's defenses are weakened or when medical tools breach the skin, these residents can sometimes escape their usual neighborhood and enter the bloodstream, leading to serious illness. One such organism is Mycoplasma hominis, a tiny bacterium that lacks a protective outer shell, making it invisible to many standard antibiotics that work by attacking cell walls. While this microbe is well-known for causing local infections, it is extremely rare for it to travel through the blood to infect the entire body, especially through medical tubes inserted into the veins. Understanding how these rare infections happen is crucial for doctors treating patients with severe heart failure who rely on life-support machines, as the wrong treatment can allow the infection to spread unchecked.

This story begins in a hospital in Haining, China, with a 68-year-old man who arrived in July 2025 suffering a severe heart attack. His heart was struggling to pump blood, and his blood pressure had dropped dangerously low. Doctors quickly placed a stent to open a blocked artery and inserted a mechanical device called an intra-aortic balloon pump into an artery in his right leg to help his heart circulate blood. For the first week, the treatment worked well; his heart function improved, and the balloon pump was removed. But then, the patient began to run a fever, and his breathing became difficult again. His body was fighting a fire that the doctors could not see. To help his kidneys manage fluid and to wash out inflammatory chemicals from his blood, doctors inserted another tube into a vein in his left leg to perform continuous kidney filtration. Despite using strong antibiotics to cover common bacteria, the patient's fever persisted, and his inflammatory markers, which act as a measure of the body's alarm system, continued to climb.

By the second week, the patient's condition worsened rapidly. His heart began to fail again, and his blood pressure required massive doses of medication to stay stable. Doctors placed him on a machine that acts as an artificial heart and lung, known as extracorporeal membrane oxygenation, to keep him alive while they searched for the cause of his illness. They took samples of his blood, urine, and the tips of the tubes that had been inserted into his body to look for the source of the infection. While the patient was transferred to a larger hospital in Hangzhou for advanced heart support, the microbiology lab back in Haining was examining the blood samples under a microscope and using a high-tech scanner that identifies bacteria by their unique molecular weight. On the blood culture plates, they found tiny, needle-like colonies that looked like fried eggs under the lens. The scanner confirmed the identity of the culprit: Mycoplasma hominis.

This discovery was significant because it was the first time this specific organism had been linked to an infection caused by a catheter in a blood vessel. The bacteria were not found in the patient's urine or sputum, only in the blood, suggesting that the infection likely entered through the tubes placed in the groin area, right next to where the bacteria naturally live. Because Mycoplasma hominis does not have a cell wall, the standard antibiotics the patient had been receiving were useless against it. The medical team switched to a newer, specialized antibiotic called omadacycline, which is effective against this type of bacteria. After nearly a month of this targeted treatment, the infection was brought under control. The patient eventually received a permanent mechanical pump to support his heart and was discharged in stable condition.

The case highlights a critical lesson for medical care: when a patient with a tube in the groin develops a fever that does not respond to standard antibiotics, doctors must consider rare, atypical bacteria that live in the genital tract. These organisms are invisible to many common tests and immune to many common drugs. The researchers also noted that the infection seemed to trigger a dangerous blood clot that blocked the patient's heart stent, a complication that can occur when the body is fighting a severe infection. This event suggests that the presence of this specific bacteria can make the blood more prone to clotting, a connection that requires further study. Ultimately, this report serves as a reminder that in the complex world of life support and invasive procedures, the usual suspects are not the only ones capable of causing harm, and identifying the true cause of an infection often requires looking beyond the expected.