Phenotypic and genomic changes in enteric populations during long-term ICU patient hospitalization: the role of RamR regulation.

Unlabelled: Acquired antimicrobial resistance and metabolic changes are central for bacterial host adaptation during the long-term hospitalization of patients. We aimed to analyze the genomic and phenotypic evolution of enteric populations in long-term intensive care unit (ICU) patients. Weekly rectal swabs were prospectively collected from all patients admitted to the ICU in a teaching hospital from December 2018 to February 2019. The inclusion criterion for patients was hospitalization for more than 15 days in the ICU without any history of hospitalization or antibiotic treatment for the 3 months prior to admission. Among them, enteric species complex (KpSC) populations were detected. For each isolate, extensive antimicrobial resistance profiles were determined using the disk diffusion method, and the whole genome was sequenced using an Illumina platform. typing methods, such as Multilocus Sequence Typing (MLST), core-genome MLST, SNP typing, resistome characterization and mutation point detection, were applied. During the study period, 471 patients were admitted to ICUs. Among them, 21 patients met the inclusion criteria, and only 5 patients (24%) carried unique and distinct KpSC populations during 2-10 weeks in the gut that as detected at admission and excluding acquisition during the ICU stay. One patient showed a rare ST1563 persistent carriage for 7 consecutive weeks, which displayed important antimicrobial resistance phenotype changes in the 2 last weeks. In-depth characterization and RNA sequencing of these strains revealed a mutation within the transcriptional regulator resulting in overexpression of the regulator and decreased expression of , which controls antibiotic efflux. This mutation also impacts tolerance to biliary salts. This study revealed the importance of endogenous colonization of KpSC populations in the gut throughout the patient's long-term ICU stay and highlighted the role of in drug susceptibility.

Importance: The species complex (KpSC) is one of the major causes of nosocomial infections, especially in intensive care unit (ICUs). These bacteria are frequently highly resistant to antibiotics, leading to an increase in morbidity and mortality. The origins of multidrug-resistant KpSC strains isolated from ICU patients are still unclear, with at least two hypotheses of acquisition paths: (i) endogenous KpSC populations that are or became resistant to antibiotics and/or (ii) hospital acquisition of circulating KpSC clones. Genomic changes observed in this study might reveal mechanisms to better adapt to KpSC in the patient's gut in the face of heavy ICU medical care pressure.