Highlights ■ Oral and tracheal pathogens persisted throughout mechanical ventilation. ■ S. aureus showed consistent oral-tracheal correlations at both time points. ■ Tracheal K. pneumoniae load increased after 48 hours and  exceeded oral load. ■ The oral microbiota may contribute to lower respiratory tract colonization and systemic infection. ABSTRACT Objective: To investigate the prevalence, co-occurrence, and temporal dynamics of Staphylococcus aureus, Klebsiella pneumoniae, Streptococcus pneumoniae, and Pseudomonas aeruginosa in oral and tracheal samples from critically ill patients receiving mechanical ventilation. […]