How the Bacteria in your Gut Compete for Survival

How the Bacteria in your Gut Compete for Survival

  • Probiotics 101

  • By Desiree Nielsen, Registered Dietitian

    The digestive tract is home to trillions of live microbes. No matter how many times we hear that statistic, it still inspires awe. Living along the entire length of your gut, that community of trillions represents about one thousand different species of bacteria, together with archaea (single-celled organisms), viruses and yeasts. Some are most at home in the acidic contents of your stomach, like Helicobacter pylori. Others prefer the slow-moving space within the colon while yet others choose to get cozy, deep into the folds of your intestinal walls like Bacteroides fragilis.

    As with any living thing, in order to thrive, microbes need access to the right pH, the perfect amount of (or lack of) oxygen and enough food so they can keep multiplying. This means that life within the confines of the gut is a competitive place.


    Bac Against Bac

    Given limited resources, the success of one microbe may mean that another dies off – there is only so much space and food available to feed the hungry trillions. So survival is dependent on the ability of bacteria to compete, which they do in several ways:


    1. pH: beneficial microbes like Lactobacillus acidophilus create short-chain fatty acids such as lactate that lower the pH of the gut space. This favours the growth of more lactobacillus while making it difficult for other, less helpful microbes such as pathogenic strains of E.coli, to survive.


    1. Antimicrobials: bacteria can produce many different types of antimicrobials, such as hydrogen peroxide, antimicrobial peptides or bacteriocins that kill off competing strains.


    1. Nutrients: as nutrient availability is limited in the gut, strains that grow and ferment available nutrients remove them from the environment, and inhibit the growth of other strains. However, the metabolites they produce, such as short-chain fatty acids or sugars liberated from other compounds, can also drive the growth of other microbes.


    1. Space: as one strain grows, it takes up physical space that will limit the growth of other strains. Certain bacterial species, such as Lactobacillus rhamnosus, can also create sugar ‘bubbles’ called biofilms that strengthen the physical defenses of any complementary strains, improving nutrient availability and oxygen levels while keeping other strains out.


    1. Interaction with the host immune system: the presence of certain bacteria can interact with your immune system in a way that benefits them to the detriment of others. This interaction can also benefit you – or not. For example, certain bacteria thrive in – and literally feed off of - an inflammatory state, so they can drive inflammation by damaging the gut lining to perpetuate inflammation.


    Striking a Balance

    Bacteria are one of the most successful – if not the most successful – living things on the planet. Bacteria can divide and double their numbers in as little as 20 minutes, which means they can multiply quickly and take up a lot of real estate in the gut, provided there is enough food and space available to support that growth. And the type of food available matters: it’s becoming clear that how we choose to eat plays a large role in which microbes thrive in our gut. We digest and absorb as much as 95% of everything we eat – what is left over is available for your bacteria to ferment. Eat more bran, more lentils, or more meat, and the species that live on those foodstuffs will have an advantage. Amazingly, we can become the food source for some microbes; bacteria like A.muciniphila eat proteins found in the mucus that lines our gut.

    As you can see, the complexity of bacterial competition is staggering. Hopefully, the end result is a harmonious balance of microbes that keep us healthy and thriving. However, that balance can be lost, more often than we might expect, creating a state called dysbiosis. Dysbiosis occurs when the typically large community of beneficial bacteria is diminished, allowing the small amount of opportunistic pathogens naturally present to multiply.

    It could be a nasty bout of traveller's diarrhea that shifts the balance. Or a period of stress and a high fat, high sugar diet. Or, a course of antibiotics. Nowhere is this imbalance more evident than in the story of Clostridium difficileClostridium difficile, or C.diff, is present in many of our digestive tracts; however, when the conditions are right, certain strains of C.diff begin multiplying and produce toxins that cause inflammation and diarrhea. Clostridium difficile-associated diarrhea can be fatal and it is increasingly antibiotic-resistant.

    C.diff is particularly tough to fight because it forms spores that lay dormant until the conditions are right for growth. Think of spores as a hard outer casing that helps bacteria like C.diff  or Clostridium botulinum survive even without proper nutrition, proper pH or when exposed to antimicrobial substances like alcohol. However, spores don’t cause the infection; actively growth bacteria do. What creates that shift?

    Antibiotic use sets the stage for growth of these microbes as it kills off many of the beneficial bacteria keeping you well. For example, beneficial bacteria transform the bile secreted into your gut into new substances, called secondary bile salts, which are thought to inhibit the growth of Clostridium difficile. There is evidence that post-antibiotic use, fewer beneficial bacteria mean fewer secondary bile salts, giving C.diff the green light to start their growth cycle.

    Antibiotic use also creates microbial shifts that result in the liberation of sialic acid from the mucin proteins within the mucus layer of the gut – free sialic acid appears to drive the growth of both C.diff and harmful strains of E.coli.


    Keeping the Peace

    As you can see, bacterial competition is another reason why the balance of bacteria in our gut is so critical to maintaining good health – and why when dysbiosis is present, it’s so difficult to repair. The reason we take probiotics is to help us protect – or restore – this delicate balance.


    By providing live and active bacteria in the right dose, probiotics can stand in for the competitive functions of our own resident bacteria such as acidifying the gut, creating bacteriocins and forming bio films. The three unique strains in Bio-K+Lactobacillus acidophilus CL1285®Lactobacillus casei LBC80R® and Lactobacillus rhamnosus CLR2® have been shown effective in not only supporting a healthy, balanced gut flora but also fighting E.coli and C.diff. In fact, in the research, Bio-K+ has been proven to neutralize the effects of the toxins released by C.diff bacteria, which is why Bio-K+ is Health Canada-approved to help prevent C.diff-associated diarrhea when taken with antibiotics.

    However, given that bacterial competition exists, you may ask yourself – what’s actually happening in my probiotic? How do I know that the strains are all not just fighting each other off?

    This is where Bio-K+ stands apart. Whenever more than one strain is present, you need to study whether they compete with each other in the finished product. The three live Lactobacillus strains are fermented together in the bottle, with demonstrated synergy. In fact, the three strains in Bio-K+ appear to be even stronger together than individually.

    Like any society, your gut microbiota is actively engaged in striking a balance between individuals – and microbial competition is one of the main reasons that your gut bacteria help you fight off infection. If you want to maintain that balance, eat a variety of plant foods and help your gut bacteria fight the good fight with a daily dose of Bio-K+.


    Do you have any other questions about the health of your microbiota or C.diff bacteria? Ask us in comments below. If you are looking to stock up on Bio-K+, head to our store locator. For more information on Bio-K+, probiotics and digestive health, contact us, find us on Facebook and Instagram or join our community



    1. Introduction to the human gut microbiota - PMC (

    2. Interactions between the microbiota and pathogenic bacteria in the gut - PMC (


    4. Multifaceted Interfaces of Bacterial Competition - PMC (

    5. Clostridium difficile virulence factors: Insights into an anaerobic spore-forming pathogen - PMC (


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    Desiree Nielsen Registered Dietitian
    About the author
    Desiree Nielsen is a registered dietitian, author and host of the vegetarian cooking sshow, The Urban Vegetarian. Desiree takes an evidence-based, integrative approach to her dietetics work, with a focus on anti-inflammatory, plant-centredcentered nutrition and digestive health.
    View all articles by Desiree Nielsen
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