PhD Scientific Days 2025

Poster Session II. - J: Theoretical and Translational Medicine

Dysbiosis in Critical Illness

Name of the presenter

Karim Dilan Mark

Institute/workplace of the presenter

Semmelweis University, Department of Anesthesiology and Intensive Therapy & Centre for Translational Medicine, Budapest, Hungary

Authors

Dr. Dilan Mark Karim¹, Péter Fehérvári², Caner Turan¹, Péter Hegyi², Zsolt Molnár¹, Krisztina Madách¹

1: Semmelweis University, Department of Anesthesiology and Intensive Therapy & Centre for Translational Medicine, Budapest, Hungary
2: Semmelweis University, Centre for Translational Medicine, Budapest, Hungary

Text of the abstract

Introduction
The human microbiome has a critical role in immune regulation, nutrition, and pathogen defence. Dysbiosis, characterized by the loss of microbial diversity and a pathological change in composition, is prevalent in critically ill patients and has been linked to poor outcomes. The extent of this diversity loss, and its potential risk factors remain unclear.
Aims
To assess the extent of microbial diversity loss in critically ill patients and to identify possible risk factors.
Methods
A systematic review and meta-analysis were conducted following the Cochrane Handbook and PRISMA guidelines. We included all studies reporting alpha diversity of the gut and/or lung microbiome of critically ill patients. Raw analysis of diversity measures was performed and studies with temporal data were included in a secondary analysis to assess diversity change over time. For improved comparability, we regrouped studies with healthy controls and calculated standardised mean differences (SMD) between healthy and critically ill populations, reducing heterogeneity arising from differences in sampling, sequencing and data analysis methods. Potential risk factors were examined for interactions with microbial diversity.
Results
The analysis included 104 studies from an initial pool of 18,547. The pooled Shannon diversity index of the gut microbiome was 3.27 (95% CI: 3.01–3.54, n=2,245). The pooled Chao1 richness index was 320 (95% CI: 221–419, n=1,063). A minor change was seen over time in pooled data, but the between-study differences were extensive.
In the standardized comparison, diversity and richness were significantly lower in the critically ill, with a Shannon index SMD of -0.91 (95% CI: -1.25 to -0.58, n=1,189) and a Chao1 index SMD of -1.54 (95% CI: -2.32 to -0.77, n=648). There was no significant difference in diversity loss between adult and pediatric populations (X²=2.53, p=0.11).
No significant interactions between diversity and the collected risk factors were identified.
Conclusion
Microbial diversity is significantly reduced in critically ill patients, but methodological variability limits current evidence and comparability of studies. We suggest a consensual, standardised framework for how evidence is collected and recommend an individual participant data meta-analysis approach to identify modifiable risk factors and possible interventions.
Funding
None