New research shows a rare but often fatal complication among lung transplant patients is likely caused by bacteria normally found in the urinary tract.

Dr. Ankit Bharat, a thoracic surgeon and surgical director at the Northwestern University Feinberg School of Medicine in Chicago, found elevated levels of ammonia in a 44-year-old double lung transplant patient a week after transplant surgery. Reasons for the patient's hyperammonemia weren't clear.

A brain scan showed no abnormalities, and dialysis did not decrease ammonia levels to a safe level. After experiencing brain swelling and falling into a coma, the patient died 40 days after surgery.

Bharat's team found the bacterium Ureaplasma urealyticum in the deceased patient's lung tissue. U. urealyticum or a related microbe U. parvum were also found in the lung tissue of three other double-lung transplant patients who had died from complications of hyperammonemia.

Bothbacteria usually live in the body's urinary tract where they break down urea, producing ammonia as a byproduct. The ammonia that's secreted is removed from the body in urine, so little ammonia is found in blood gases.

The same bacteria strains were also found in two double-lung transplant patients who had hyperammonemia but were still living. After treatment with a course of antibiotics, the patients recovered. Researchers found no evidence of the microbes in 20 double-lung transplant patients who did not experience increased ammonia levels.

Researchers say it's unclear why the bacteria sometimes spread to other areas of the bodies of transplant recipients and cancer patients where they cause infection and ultimately death. The team theorized these patients' compromised immune systems might allow the bacteria to take advantage of the body's weakened defenses. Or, given that the bacteria were found in a one donor's lungs prior to transplant, the microbes and their ability to product deadly amounts of ammonia could enter the recipient's body when the donated organs are surgically transplanted.

Regardless of why or how the bacteria invade the lungs of some organ recipients, Bharat's research suggests a potential course of treatment for lung transplant recipients who have hyperammonemia.

The initial patient Bharat and colleagues studied received the antibiotic azithromycin, which was not effective against the U. urealyticum. The bacteria could have become resistant to that specific drug, the team wrote. To avoid resistance, Bharat suggests using a combination of drugs from the three antibiotic families to which the microbes are vulnerable.

Bharat indicated that Ureaplasma microbes are difficult to diagnose because they don't grow in the routine cultures hospitals perform when identifying bacterial infections. For this reason, patients with unexplained hyperammonemia should be tested specifically for their presence.