Beyond the cuff - characterising biofilm-forming microorganisms on endotracheal tubes in critically ill patients

Background/Aims: Mechanical ventilation, commonly used for acute respiratory failure in intensive care units (ICUs), usually involves tracheal intubation with an endotracheal tube (ETT). Microorganisms can attach to the ETT surface within hours, forming biofilms that may serve as infection reservoirs and enhance microbial tolerance to external factors, such as antimicrobials. This study aimed to characterise the diversity of biofilm-forming microorganisms on ETTs, examining differences in biofilm microbial communities from sections above and below the cuff.<br/><br/>Methods: Critically ill adults requiring mechanical ventilation through an ETT who were admitted to two participating ICUs within the Belfast Health and Social Care Trust, Northern Ireland, were prospectively recruited between April 2023 and March 2024. Following extubation, pre-defined 1 cm2 sections directly above and below the cuff were excised and biofilms removed. The viable counts (density) of bacteria and fungi (colony-forming units per 1 cm2 section [CFU/cm2]) were determined by extended quantitative culture. Isolate identification was done by MALDI-ToF and/or 16S rRNA (bacteria) or ITS (fungi) marker gene sequencing. Routine microbiological investigations of respiratory samples (secretions, bronchoalveolar fluid, pleural fluid) during hospital admission were recorded, when available, for participants. The study was approved by the Social Care Research Ethics Committee (20/IEC08/0025).<br/><br/>Results: Forty participants (mean age, 58 years; 15 female) were included. The median (range) intubation duration was 3 days (&lt;24 hours to 14 days). Overall, 433/456 (95.0%) ETT isolates recovered were identified to the species- (or genus-) level with a median (range) richness of 2 (0-12) in biofilms above and 2 (0-17) below the cuff (p=0.5). No microorganisms were cultured in at least one section of five participant ETTs. There was no difference in the microbial density (geometric mean [95% confidence interval]: above cuff, 2.0 x103 [4.0 x102 – 7.9 x103] CFU/cm2; below cuff, 1.6 x103 [4.0 x102 – 5.0 x103] CFU/cm2; p=0.7) or in the microbial diversity between sections (Shannon-Wiener diversity, median: above cuff, 0.951; below cuff, 0.693; p=0.8). Microbial biofilm communities were more similar within than between patient ETTs. Among the taxa cultured, Candida albicans was the most prevalent (above cuff, 7/40 [17.5%] participants; below cuff, 11/40 [27.5%] participants). Fungal taxa were identified in 32 biofilms and usually co-cultured with bacterial taxa (84% of the time). Recognised respiratory pathogens including Staphylococcus aureus, Pseudomonas aeruginosa and Enterobacteriaceae were also identified in the ETT biofilms. Pathogens were found in 18 participants’ respiratory samples, of whom 9 had the same pathogen recovered from their ETT biofilm.<br/><br/>Conclusion: Community profiling showed that microbial biofilms were similar regardless of their origin (above or below the cuff), with fungi frequently detected. Generally, viable microorganisms in most ETT biofilms were present in low density; nonetheless, recognised respiratory pathogens were commonly present. Further studies will investigate the microbial community composition and structure in ETT biofilms using next-generation sequencing.<br/><br/><br/>