De Novo or Persistent Pseudomonal Airway Colonization After Lung Transplantation: Importance for Bronchiolitis Obliterans Syndrome?

Abstract

Recently, Botha et al. (1) showed that de novo colonization of the lung allograft by Pseudomonas is strongly associated with the subsequent development of bronchiolitis obliterans syndrome (BOS) after lung transplantation (LTx). This is an interesting and an important finding; however, we can hardly agree with the authors’ statement that persistent colonization “does not seem to predispose to the development of BOS.” In fact, we recently also demonstrated that pseudomonal airway colonization after LTx indeed is a risk factor for BOS (2), which is corroborated by the authors’ results. Yet, re-analyzing the data from our study demonstrated results that are exactly opposite to those of the authors’, namely freedom from BOS was significantly shorter mainly in those patients with persistent (i.e., with an existing pseudomonal reservoir present pretransplant, as defined by the authors) airway colonization, whereas the patients with de novo colonization after LTx seemed to have a somewhat better BOS-free survival (Fig. 1). In both studies, LTx recipients with persistent colonization were mainly cystic fibrosis (CF) patients and those with de novo colonization were mainly patients with chronic obstructive pulmonary disease; therefore, this discrepancy raises some questions. Furthermore, their suggestion that persistent allograft colonization “may represent simple recolonization … with little pathological impact on otherwise healthy airways” is contradicted by the fact that both transient and persistent pseudomonal airway colonization are associated with neutrophilic airway inflammation (2–4), which can lead to a self-perpetuating cycle of airway damage and subsequently airway remodeling after LTx, as is also seen in chronic obstructive pulmonary disease (5), CF (6), and bronchiectasis (7). Moreover, in our own study, we could demonstrate a significant correlation between the postoperative day of recolonization and development of BOS stage more than or equal to 1 in the CF patients developing BOS, suggesting that particularly early recolonization of the healing allograft by the resident bacteria in the upper respiratory tract during the first days or weeks after LTx is detrimental for the evolution to BOS. In the end, both articles confirm the importance of pseudomonal colonization for the development of BOS; yet, we would like to ask the authors how they could explain the discrepancies between their current results and our recent findings.FIGURE 1.: Freedom from BOS ≥1 of all recipients (n=92), dichotomized to presence (n=39) (de novo, n=19 vs. persistent, n=20) or absence (n=53) of pseudomonal airway colonization after LTx. Survival curve was censored to survival at 3 months, ***P<0.001.Robin Vos Bart M. Vanaudenaerde Stephanie I. De Vleeschauwer Dirk E. Van Raemdonck Lieven J. Dupont Geert M. Verleden Lung Transplantation Unit Katholieke Universiteit and University Hospital Gasthuisberg Leuven, Belgium