The human microbiome is the diverse population of microorganisms that live on and in the body. Many thrive on the skin and in the mouth, but the majority live in the intestines. Over the last decade or so, microbiologists have become increasingly aware of how a person's microbial mix likely plays a critical role in a variety of medical conditions, as well as how that person responds to treatment.
Maintaining a healthy balance of gut bacteria is particularly difficult in a hospital's intensive care unit, or ICU. Every year, more than 5.7 million critically-ill patients are admitted into ICUs in the United States. Treatments like strong antibiotics (to prevent infections), opioids (for pain), or blood pressure-supporting medications can save the sickest patients and prevent death, but they can also wipe out or change colonies of health-promoting microbes. Researchers have long suspected a connection between critical illness and a gut microbiome imbalance, or dysbiosis. This can leave a person vulnerable to the rapid growth and colonization of disease-causing bacteria and hospital-acquired infections – conditions that can lead to fatal conditions like sepsis.
“The original disease is bad, but our treatments are also damaging to normal bacteria, and potentially to a patient's long-term outcome,” says Paul Wischmeyer, an anesthesiologist at the University of Colorado-Boulder who also runs a lab dedicated to improving outcomes for critically-ill patients. “Sometimes we have to do these treatments, but what are we going to do to correct the damage our treatments with antibiotics and other drugs do?”
Many ICU patients suffer long-term damage from treatments, he says. “Are we creating survivors or victims in our ICUs today, and can we do better?”
Wischmeyer is passionate about looking for nutritional interventions aimed at restoring a critically ill patient's bacterial balance. But developing such interventions will require deep knowledge of how patients' microbiomes respond to the conditions of the ICU – knowledge that's been lacking, mostly. Previous studies have tracked microbial changes in individuals and small numbers of ICU patients, but Wischmeyer had something bigger in mind.
He recently led a study to fill some of that knowledge gap. He and his collaborators – including dietitians, pharmacists, statisticians, critical care physicians, and computer scientists – collected fecal, stool and oral samples from 115 patients admitted to the ICUs at four hospitals in the United States and Canada. They analyzed the microbiomes of those samples 48 hours after a patient was admitted, and again when the patient was discharged (or 10 days later, whichever came first). In a new paper in mSphere, they describe what they found.
As they suspected, they found that ICU patients had lower abundances of health-promoting bacteria and higher levels of pathogenic species, compared to healthy patients. Wischmeyer says he was astonished at how rapidly pathogenic bacteria flourished.
“In some cases, those organisms became 95 percent of the entire gut flora – all made up of one pathogenic taxa – within days of admission to the ICU,” he says. “That was really striking.” Some patients, in fact, were hosting microbiomes that had more in common with corpses than with healthy people.
Wischmeyer, who will move his lab to Duke University in the fall, sees a variety of ways to use the study's findings. In addition to designing recovery plans aimed at restoring healthy bacteria in the gut, researchers may use this approach to gauge a patient's response to therapy. “Can we take these data and begin to make predictions about what happens to some of these patients?” he wonders.
The roots and implications of the study are personal for Wischmeyer. During high school, more than two decades ago, doctors diagnosed him with inflammatory bowel disease. He has undergone more than 20 surgeries to treat the condition.
“The drugs they treated me with often made me worse, not better,” he says. His symptoms first materialized soon after he'd been treated with antibiotics for strep throat, and he wonders if that treatment treatment triggered the disease by changing the bacterial balance of his gut. The experience drove him to learn more about gut microbes and their role in health.
“I became passionate about nutrition and how the gut can be affected by changes in our “health” environment,” he says. He hopes his findings will lead to future studies on new ways to correct dysbiosis. “I think this is a first step of a large road map for improving health by optimizing the makeup of the bacterial “friends” that share our body with us throughout life.”