Microbiological Dynamics Before and After Lung Transplantation: Clinical Interpretation and Prognostic Implications

Respiratory cultures before and after lung transplantation are frequently obtained but often difficult to interpret. A positive culture may represent donor-derived organisms, recipient reservoir recolonization, hospital acquisition, transient colonization, invasive infection, or a marker of evolving graft vulnerability. This review summarizes how respiratory microbiology changes across the lung transplant timeline and proposes a practical framework for clinical interpretation. Conventional culture-based studies and recent airway microbiome literature are integrated to examine donor-recipient attribution, pre-transplant colonization, disease-specific reservoirs, single-lung transplantation, and pathogen-specific risk. Pre-transplant recipient colonization, particularly with multidrug-resistant gram-negative organisms, appears more consistently associated with early post-transplant pneumonia and short-term outcomes than donor culture positivity alone when targeted antimicrobial therapy is used. Disease-specific patterns are also important: cystic fibrosis and bronchiectasis favor recolonization from persistent reservoirs, whereas single-lung transplantation creates a dual-airway ecosystem in which the native lung may remain microbiologically relevant. Persistent or recurrent isolation of organisms such as Pseudomonas aeruginosa, Burkholderia cenocepacia, Staphylococcus aureus, Aspergillus species, and nontuberculous mycobacteria should be interpreted in relation to symptoms, imaging, lung function, sampling source, and timing from transplant. Contextual interpretation of respiratory cultures may improve antimicrobial planning, donor acceptance decisions, stewardship, and long-term graft surveillance.