Bacterial aggregates, comprising single or multiple species, are prevalent across diverse ecological niches. Such cellular clustering is regarded as a shield against environmental adversities and suspected to be the initial phase in biofilm formation. This ubiquitous phenomenon can be observed among both environmental and pathogenic bacterial populations. Thus, raising interest of aggregation within human microbiomes. Particularly in highly competitive environments like the human intestine, the protective characteristic of multicellular aggregates is thought to lead to a selective advantage for pathogenic species. Perturbations in the equilibrium of the intestinal microbiota may promote the proliferation of unfavorable bacteria. Moreover, dysbiosis is frequently observed during or after sepsis. However, the specific role of bacterial aggregation in this context remains elusive.

To investigate the impact of aggregation on a disbalanced human gut microbiota, Enterobacteriaceae were isolated from fecal samples of intensive care patients (from study MS-ICU) who were treated with the antibiotics meropenem, piperacillin/tazobactam, or with no antibiotics. Isolates were screened for their ability to aggregate and form biofilms. As bile acids accumulate in patients" blood during sepsis, we also assessed the influence of this substances on cell size, shape and aggregation via cell counting and microscopy.

Our study demonstrates the presence of several aggregate- and biofilm-forming Enterobacteriaceae among the surviving strains isolated across all patient treatment cohorts. Additionally, bile acids significantly influence those processes. We suggest that bacterial aggregation and biofilm formation may promote the survival of specific strains within the gut. Subsequent experiments will consider the impact of host-pathogen interactions and also of antibiotics. Integrate our results, we aim to understand the role of bacterial aggregation in the maintenance of a balanced human intestinal microbiota.