Contributions of Intestinal Bacteria to Nutrition and Metabolism in the Critically Ill

Abstract

SYNOPSIS Important advances in the study of bacteria associated with the human gastrointestinal tract have significant implications for clinicians striving to meet the metabolic and nutritional needs of critically ill patients. A transition from culture-based to culture-independent studies of the intestinal microbiota has ushered in a new era of laboratory and clinical studies in this field. These studies are helping to clarify the important role of bacteria in carbohydrate metabolism, and are providing new evidence that highlights the role of bacteria in protein and lipid homeostasis. We know that during periods of caloric excess or deprivation, microbial populations in the GI tract are clearly altered; however the molecular etiology for such changes remains elusive. Similarly, little is known about how microbial ecology changes before, during, and after critical illness. Nevertheless, several approaches, e.g. probiotic administration, have been employed to manipulate gut microbial communities in the ICU. In this review we offer a broad overview of the importance of the host-microbe relationship, discuss what is currently known about the role of gut microbes in nutrition and metabolism in the healthy human host, review how gut microbes are impacted by critical illness, and discuss interventions that have already been utilized to manipulate the gut microbiome in ICU patients.

Engineering Microbiomes to Improve Plant and Animal Health

“…Microbiomes are not passive players [6,7]; rather, microbes can alter host development, physiology, and systemic defenses [2,8,9], enable toxin production and disease resistance [10,11], increase host tolerance to stress and drought [12][13][14], modulate niche breadth [15], and change fitness outcomes in host interactions with competitors, predators, and pathogens [6]. Because microbiomes can encompass a hundred-fold more genes than host genomes [16], and because this 'hologenome' of a hostmicrobiome association can vary over space and time [17,18], microbiomes can function as a phenotypically plastic buffer between the host-genotype's effects and the environmental effects that interact to shape host phenotypes. Expression of virtually any host phenotype thus depends to some extent on the presence and taxonomic makeup of host-associated microbes.…”

Dysbiosis in the intensive care unit: Microbiome science coming to the bedside

“…indigenous microbes that provide benefits to the human host), with resultant increased vulnerability to secondary pathogen intrusion, and enrichment for antibiotic-resistance genes [16]. Host nutrition is also likely important, because intestinal microbiota rely mainly on availability of enteral nutrients for their survival, and critical illness places them in an acute starvation state [17]. Additionally, pharmacological interventions may alter specific body-site conditions (e.g.…”

“…Finally, the ICU environmental ecosystem, including room surfaces, devices or even the hands of healthcare providers may form reservoirs of microbes that can colonize vulnerable patients, as shown in the case of gut colonization of very low birth weight infants by bacteria present in their room environment [18]. Overall, we have only limited knowledge of the impact of ICU care on the microbiome [17]. …”

“…A major metabolic role of gut microbes is the fermentation of dietary fiber into short-chain fatty acids (SCFA), among which butyrate serves as a primary energy source for the colonic epithelium and preserves gut integrity [19]. With a rapid and persistent drop in fecal SCFA concentration with sepsis [21], the mucus epithelial barrier is degraded opening up ports for pathogen translocation, and epithelial apoptosis occurs resulting in malabsorption of nutrients, diarrhea and fecal energy loss [17,22]. Intestinal microbiota are also considered major tonic activators of host immunity against infections, involving both innate (via granulopoiesis stimulation and antimicrobial peptide production) and adaptive (through regulatory and Th17 T cell differentiation) mechanisms [23].…”

Is there a link between autism and glyphosate-formulated herbicides?

“…Gut commensals provide many essential nutrients to the body [39]. In particular, Lactobacillus participates in bacterial fixation of inorganic selenium into more bioavailable organic forms such as selenocysteine and selenomethionine.…”