International Business Department           Liu Bojia           October 25, 2023

  Our intestines provide a home for hundreds of millions of diverse bacteria. These little things reside in our intestines to help us digest, provide us with indispensable vitamins, and more than anything else, help us fight off foreign pathogenic bacteria. Without gut flora - for example, by growing up in a completely sterile environment, or by removing it completely with antibiotics - the results of animal experiments have shown that this can rapidly increase the risk of infection when subsequently exposed to the outside world.

  While many studies have let us know that it is important to maintain a balanced gut flora, the question of what gut flora composition is better at providing protection, or to put it bluntly, which probiotic supplementation is good for your health, has yet to be settled.

  A recent study published in the leading academic journal Science provides a seemingly simple answer: a more diverse flora is good for health. And scientists explored the mechanism behind it and found that the reason is surprisingly easy to understand.

  In this study, researchers at the University of Oxford in the UK examined how gut bacteria fight off potentially disease-causing "bad bacteria" by selecting more than 100 different strains of gut bacteria and two common disease-causing organisms, Klebsiella pneumoniae and Klebsiella spp. Klebsiella pneumoniae and Salmonella enterica, two common pathogens, and cultured them together in different combinations.

  As a result, they observed that when these gut bacteria were "singled out" against the pathogenic bacteria, it was difficult for any one of them to contain the spread of the pathogenic bacteria; however, when up to 50 species of bacteria were cultured together, the pathogenic bacteria grew only 1/1,000th as efficiently as they did when co-cultured with a single gut bacterium. This effect held true not only in the environment of in vitro bacterial culture, but also when the intestines of germ-free mice (which had no resident intestinal bacteria prior to the experiment) were used as the culture environment.

  These results suggest that resistance to pathogenic bacterial colonisation is a collective property of gut bacteria when they combine to form colonies. Interestingly, the researchers also found that there are some bacterial species that are "cornerstones" of the gut flora, which do not provide much protection on their own, but when present in the colony can make the colony more protective.

  Analysing the reasons further, the researchers found that they can be explained by a simple ecological fundamental: diverse gut bacteria effectively contain the growth of pathogenic bacteria by consuming a greater diversity of nutrients.

  A protective gut flora requires both bacterial species similar to the pathogenic bacteria, whose metabolic needs overlap to a higher degree, to "grab" the nutrients that the pathogenic bacteria need most first, and additional bacterial species that are more distantly related to the pathogenic bacteria to ensure that nutrients are blocked, so that the pathogenic bacteria can't eat anything. "The key is to have the nutrient utilisation curves of the bacteria and pathogenic bacteria overlap." The researchers concluded.

  Based on this speculation of the principle of nutrient blockade, the researchers conducted computational simulation analyses to predict whether different species compositions of gut flora would provide more or less protection when faced with a new pathogenic bacterium by assessing the genomic and metabolic requirements of different bacterial species. And in subsequent experiments, the results confirmed the predictions of the computer simulations.

  The study authors believe that these findings could explain why bacterial infections such as Klebsiella pneumoniae are often more likely to occur after treatment with antibiotics, and that this is related to the fact that antibiotic treatment reduces the species diversity of the gut flora. They hope to use the predictive methods developed in this study to develop new strategies for optimising gut health by rationally designing the gut flora.