Temporal Changes in Tracheal Aspirate Pathogens, Resistance Patterns, and Inflammatory Biomarkers in Critically Ill Patients: An Exploratory Retrospective Cohort Study

Abstract

Objective: Nosocomial and ventilator-associated pneumonia are major causes of morbidity and mortality in intensive care units (ICUs). Although tracheal aspirate cultures (TACs) are routinely obtained, temporal changes in antimicrobial resistance and systemic inflammation within the same patient remain poorly characterized. This study evaluated microbiological and laboratory changes using serial TAC samples. Methods: This retrospective cohort study included adult ICU patients admitted to a tertiary center between January 2022 and July 2025 who underwent at least two TACs and had complete laboratory data. Changes in pathogen distribution, antimicrobial resistance patterns, and inflammatory biomarkers between sequential TAC episodes were analyzed. Results: Forty-six patients were included, with an overall mortality rate of 97.8%. The median interval between TACs was 13.5 days. Pathogen distribution shifted toward Klebsiella spp. in the second TAC. Extensively drug-resistant isolates increased from 23.9% to 58.7%. Resistance to ceftazidime and methicillin also increased, whereas the proportion of isolates without resistance decreased. Laboratory findings demonstrated persistent physiological stress, including elevated C-reactive protein, reduced albumin, increased blood urea nitrogen/creatinine ratio, and declining blood cell counts. Conclusion: Critically ill patients receiving prolonged mechanical ventilation demonstrated temporal changes in pathogen distribution, antimicrobial resistance patterns, and inflammatory biomarkers over approximately two weeks. These findings suggest ongoing microbiological and inflammatory alterations during extended ICU stays. Larger prospective studies are needed to determine the clinical significance of these longitudinal changes.