Limosilactobacillus reuteri is a lactic acid bacterium. It is a member of the Lactobacillaceae family. It inhabits a variety of natural environments, including the gastrointestinal tract of humans and other animals. It does not appear to be pathogenic and may have health effects.
Discovery At the turn of the 20th century, L. reuteri was recorded in scientific classifications of lactic acid bacteria, though at this time it was mistakenly grouped as a member of Lactobacillus fermentum. In the 1960s, further work by microbiologist Gerhard Reuter, for whom the species eventually was named, reclassified the species as L. fermentum biotype II. Significant differences were found between biotype II and other biotypes of L. fermentum, to the point that in 1980 it was identified as a distinct species and the formal species identity, L. reuteri, was proposed. In April 2020, L. reuteri was reassigned to the genus Limosilactobacillus.
Prevalence L. reuteri inhabits multiple natural environments. It has been isolated from many foods, especially meats and dairy products. It appears to be ubiquitous in the animal kingdom, including in the gastrointestinal tracts and feces of healthy humans, sheep, chickens, pigs, and rodents. It is the only species to constitute a "major component" of the Lactobacillus genus present in the gut of each of the tested host animals, and each host seems to harbor its own specific strain. It is possible that L. reuteri contributes to the health of its host organism. L. reuteri is present as a dominant member of fermenting organisms in type II sourdoughs; several metabolic traits of L. reuteri, including exopolysaccharide formation and conversion of glutamine to glutamate, improve bread quality.
Effects
Antimicrobial Limosilactobacillus reuteri produces reuterin, reutericin 6 and reutericyclin.
Reuterin In the late 1980s, Walter Dobrogosz, Ivan Casas and colleagues discovered that L. reuteri produced a novel broad-spectrum antibiotic substance via the organism's fermentation of glycerol. They named this substance reuterin, after Reuter. Reuterin is a multiple-compound dynamic equilibrium (HPA system, HPA) consisting of 3-hydroxypropionaldehyde, its hydrate, and its dimer. At concentrations above 1.4 M, the HPA dimer was predominant. However, at concentrations relevant for biological systems, HPA hydrate was the most abundant, followed by the aldehyde form. Reuterin inhibits the growth of some harmful Gram-negative and Gram-positive bacteria, along with yeasts, fungi and protozoa. Researchers reported that L. reuteri can secrete sufficient amounts of reuterin to achieve desirable antimicrobial effects. Furthermore, since about four to five times the amount of reuterin is needed to kill "good" gut bacteria (i.e. L. reuteri and other Lactobacillus species) as "bad", L. reuteri can potentially remove gut invaders without harming other gut microbiota. Some studies questioned whether reuterin production is essential for L. reuteri's health-promoting activity. In 2008, L. reuteri was confirmed to be capable of producing reuterin in the gastrointestinal tract, improving its ability to inhibit the growth of E. coli. The gene cluster controlling the biosynthesis of reuterin and cobalamin in the L. reuteri genome is a genomic island acquired from an anomalous source.
Clinical results in humans Although L. reuteri occurs naturally in humans, it is not found in all individuals. Dietary supplementation can sustain high levels of it in those with deficiencies. Oral intake of L. reuteri has been shown to effectively colonize the intestines of healthy individuals. Colonization begins within days of ingestion, although levels drop after months if intake is stopped. L. reuteri is found in breast milk. Oral intake on the mother's part increases the amount of L. reuteri present in her milk, and the likelihood that it will be transferred to her child.
Safety Manipulation of gut microbiota is a complex process that may cause bacteria-host interactions. Although probiotics in general are considered safe, concerns exist about their use in certain cases. Some people, such as those with compromised immune systems, short bowel syndrome, central venous catheters, heart valve disease, and premature infants, may be at higher risk for adverse events. Rarely, consumption of probiotics may cause bacteremia, fungemia and sepsis, potentially fatal infections, in children with compromised immune systems or who are already critically ill.
Intestinal health One of the better documented effects of L. reuteri is a significant reduction of symptom duration in pediatric diarrheal disease. L. reuteri is effective as a prophylactic for this illness; children fed it while healthy are less likely to experience diarrhea. With regard to prevention of gut infections, comparative research reported L. reuteri to be more potent than other probiotics. Animal research reported it to reduce motor complexes and thus intestinal motility. L. reuteri may be effective treating necrotizing enterocolitis in preterm infants. Meta-analysis of randomized studies suggests that L. reuteri can reduce the incidence of sepsis and shorten the required duration of hospital treatment in this population. L. reuteri is an effective treatment against infant colic. Studies suggest that colicky infants treated with L. reuteri experience a reduction in time spent crying compared to those treated with simethicone or placebo. However, colic is still poorly understood, and it is not clear why or how L. reuteri ameliorates its symptoms. One theory holds that affected infants cry because of gastrointestinal discomfort; if this is the case, it is plausible that L. reuteri somehow acts to lessen this discomfort, since its primary residence is inside the gut.
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