*Purpose: Hyperammonemia syndrome (HS) is a rare complication that can occur after lung transplantation. This syndrome is characterized by increased ammonia levels with altered sensorium, seizures, cerebral edema, and has high mortality. The pathophysiology is still unclear, but case series have linked Ureaplasma urealyticum, Ureaplasma parvum and Mycoplasma hominis infection to HS. In particular, murine models suggest U. urealyticum may be mostly implicated. Our study aimed to explore the association between Ureaplasma and Mycoplasma airway colonization, ammonia levels, HS and mortality in lung transplant patients.

*Methods: Adults who underwent lung transplantation from July 2017 – August 2019 in our center were retrospectively identified. Our center performs routine surveillance testing for Mycoplasma and Ureaplasma using nucleic acid amplification testing (NAAT) from post-op day 1 bronchoscopy specimens. We collected baseline demographic data and examined for associations between Mycoplasma and Ureaplasma colonization, ammonia levels, and outcomes. Peak ammonia levels were compared using the Kruskal-Wallis test.

*Results: 159 patients underwent lung transplantation during the study period. Mean age was 54 (±13) years and most were male (66.6%). Most common etiologies for transplant were obstructive lung disease (35.8%) and idiopathic pulmonary fibrosis (23.2%). NAAT was performed in 147 (92%) of patients. In these patients, serum ammonia levels were collected during the first week post-transplant in 141 (95%). Mycoplasma and/or Ureaplasma colonization was found in 42 (29.8%) of tested patients. Species included M. salivarium (61.9%), U. parvum (16.6%), U. urealyticum (11.9%), M. hominis (7.1%) and M. pneumoniae (4.8%). Two patients were co-infected. Median peak ammonia levels were 51 mmol/L in those colonized with Mycoplasma spp., 67.5 mmol/L with Ureaplasma spp., and 46 mmol/L in uncolonized patients. Peak ammonia levels were significantly higher in those with Ureaplasma colonization compared with Mycoplasma (p=0.042) and uncolonized patients (p=0.005). Those with Mycoplasma (mostly M. salivarium) colonization did not have significantly higher ammonia levels compared with uncolonized patients. HS was identified in 2 patients (1.2%), both colonized with Ureaplasma, one of whom died.

*Conclusions: This is the first study demonstrating this association in a lung transplant population undergoing active surveillance for Mycoplasmataceae and reinforces the correlation between in vivo Ureaplasma airway colonization and higher ammonia levels.

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