Contribution of Uremia to Ureaplasma-Induced Hyperammonemia

Lung transplant recipients (LTRs) are vulnerable to hyperammonemia syndrome (HS) in the early postoperative period, a condition typically unresponsive to nonantibiotic interventions. HS in LTRs is strongly correlated with Ureaplasma infection of the respiratory tract, although it is not well understood what makes LTRs preferentially susceptible to HS compared to other immunocompromised hosts. Ureaplasma species harbor highly active ureases, and postoperative LTRs commonly experience uremia. We hypothesized that uremia could be a potentiating comorbidity, providing increased substrate for ureaplasmal ureases. Using a novel dialyzed flow system, the ammonia-producing capacities of four isolates of Ureaplasma parvum and six isolates of Ureaplasma urealyticum in media formulations relating to normal and uremic host conditions were tested. For all isolates, growth under simulated uremic conditions resulted in increased ammonia production over 24 h, despite similar endpoint bacterial quantities. Further, transcripts of ureC (from the ureaplasmal urease gene cluster) from U. urealyticum IDRL-10763 and ATCC- 27816 rose at similar rates under uremic and nonuremic conditions, with similar endpoint populations under the two conditions (despite markedly increased ammonia concentrations under uremic conditions), indicating that the difference in ammonia production by these isolates is due to increased urease activity, not expression. Lastly, uremic mice infected with an Escherichia coli strain harboring a U. urealyticum serovar 8 gene cluster exhibited higher blood ammonia levels compared to nonuremic mice infected with the same strain. Taken together, these data show that U. urealyticum and U. parvum produce more ammonia under uremic conditions compared to nonuremic conditions. This implies that uremia is a plausible contributing factor to Ureaplasma-induced HS in LTRs.