Microbiome of ICU Patients Transforms within Days of Admission

A new study shows that intensive care unit (ICU) patients have depleted populations of commensal, health-promoting microbes and higher counts pathogenic strains.

Researchers at the University of Colorado School of Medicine (Aurora, USA) collected fecal, oral, and skin samples from 115 mixed ICU patients across four centers in the United States and Canada to characterize the patient microbiome. Samples were collected at two time points: within 48 hours of ICU admission, and at discharge or on ICU day 10. The researchers assessed the source composition of ICU patient samples and compared them to those from the American Gut Project (AGP), mammalian corpse decomposition samples, and house surfaces.

The researchers found that between time points and within a patient, the source composition changed dramatically, creating a dysbiosis (bacterial imbalance) that worsened during the patient's stay in the hospital. The samples from ICU patients showed lower levels of Firmicutes and Bacteroidetes bacteria, two of the largest groups of microbes in the gut, and higher abundances of Proteobacteria, which include many pathogens. The study was published in the August 2016 issue of mSphere.

“We saw the rapid rise of organisms clearly associated with disease. In some cases, those organisms became 95%of the entire gut flora, all made up of one pathogenic taxa, within days of admission to the ICU. That was really striking,” said lead author anesthesiologist Paul Wischmeyer, MD. “Some of the patient microbiomes, even at the time of admission, resembled the microbiomes of corpses; that happened in more people than we would like to have seen.”

The average human body has about 100 trillion microorganisms in the gut, forming a mutualistic, symbiotic relationship with the body; 99% of the bacteria come from about 30 or 40 species. The metabolic activity performed by these bacteria is equal to that of a virtual organ, and includes fermentation of unused energy substrates, training the immune system, preventing growth of harmful species, regulating the development of the gut, producing vitamins for the host (such as biotin and vitamin K), and producing hormones to direct the host to store fats.

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University of Colorado School of Medicine