An unexpected microbe is killing organ transplant patients

A 44-year-old man appeared to be recovering nicely after a double lung transplant at Northwestern Memorial Hospital in Chicago, Illinois. A week after the surgery, however, the patient, whose own lungs had been ruined by the inflammatory disease pulmonary sarcoidosis, grew confused and then became delirious. Although a brain scan found nothing wrong, tests showed that the amount of ammonia in his blood had spiked—and continued to rise even after dialysis to remove the toxin. Forty days after his surgery, he died.

Now, a new study implicates bacteria that normally live in the urinary tract as the cause of the man’s fatal illness and the deaths of other lung transplant patients. The work suggests a way to treat a rare but deadly complication of organ transplantation and cancer treatment.

Although our bodies normally produce small amounts of ammonia when we break down proteins, liver enzymes transform it into a safer compound, urea, which is excreted in our urine. In some organ transplant recipients and cancer patients, however, the amount of ammonia in the blood explodes. Although this condition, known as hyperammonemia, is unusual, “when it has occurred, it’s been disastrous,” says pulmonologist Mark Wylam of the Mayo Clinic in Rochester, Minnesota. The brain swells, and patients fall into a coma. “The end of the ordeal is that they die,” he says.

Not only is hyperammonemia resistant to treatment and usually fatal, but the cause has also been elusive. In 2013, Wylam and colleagues discovered the likely culprit in one case, a 64-year-old woman who died from hyperammonemia after a double lung transplant. They found that her blood and tissues were positive for a type of bacterium, Mycoplasma hominis, that often causes mild genital infections in women.

[link to news.sciencemag.org]