Antibiotics are one of the main risk factors for the development of Clostridioides difficile infection (also known as Clostridium difficile, C. difficile, and C. diff). There are other potential risk factors, such as exposure to healthcare settings, but this post will focus on why antibiotics cause C. difficile.\n\n\n\n\n\n\n\nWhat is C. difficile? \n\n\n\nC. difficile is a type of bacteria that can be found in our intestines. It doesn't always cause infections, but when it does, the toxins it produces can lead to severe diarrhea (often more than 10 watery stools per day) and can sometimes lead to: severe dehydration, septic shock, and even death. \n\n\n\nC. difficile is resistant to many different types of antibiotics, and can even produce spores. These spores act almost like a seed; they are resistant to heat, almost all antibiotics, and even alcohol-based hand sanitizers. Then, once these "seeds" enter the colon, they can "germinate" and start reproducing. \n\n\n\nC. difficile can be transmitted from one person to another when these spores are ingested (often from touching contaminated surfaces and then putting your hand in your mouth). For this reason, it's very important to wash your hands with soap and water in order to physically remove C. difficile spores. Alcohol-based hand sanitizers will only redistribute C. difficile spores around your hands!\n\n\n\n\n\n\n\nThe effect of antibiotics on the microbiome \n\n\n\nThe collection of different types of bacteria that inhabit our intestines are often referred to as the microbiome. The microbiome plays vital roles in many aspects of our bodies. It is thought that there are at least 39,000,000,000,000 bacterial cells in our intestines (that's a lot of bacteria). Since they play a vital role, these are often coined "good bacteria".\n\n\n\nWhen we give antibiotics, they don't preferentially kill "bad" bacteria; they kill any bacteria that are susceptible to them. Antibiotics can usually be lumped into 2 main categories:\n\n\n\nNarrow-spectrum antibioticsThese antibiotics are very effective against some bacteria, but only a select few. So, their activity is more targeted towards a specific group of bacteria. I usually equate these to using a hunting rifle.\n\n\n\nBroad-spectrum antibioticsThese antibiotics are the big guns. They can kill many different bacteria, and are often reserved for more complicated\/severe infections. I usually equate these to using a grenade launcher. \n\n\n\nSo, when we use broad-spectrum antibiotics, we are treating the infection... but we are also killing many different types of "good" bacteria in the intestines. Whereas narrow-spectrum antibiotics will tend to not cause so much collateral damage on the "good" bacteria in the intestines.\n\n\n\nThis is why a huge part of my job is to ensure that we use the narrow spectrum antibiotics whenever possible. If we needlessly use broad-spectrum antibiotics to treat a very susceptible infection, it would be like rabbit hunting with a grenade launcher....yes it will work, but you'll also burn down half the forest while doing it.\n\n\n\n\n\n\n\nWhy do antibiotics cause C. difficile?\n\n\n\nWhen antibiotics kill off bacteria in the intestines, this will leave more "space" for the more resistant bacteria to grow (particularly with the big gun broad-spectrum antibiotics). C difficile is one of these resistant bacteria, and they can rapidly multiply when given the chance.\n\n\n\nTo use another analogy: A healthy microbiome is like a really healthy green lawn, and a microbiome post-antibiotics is more like my lawn (patchy, not healthy, full of weeds). If we then introduce some dandelion seeds (which would be like C. difficile spores), the healthy lawn stays healthy because there's no room for the weeds to grow. But, the patchy\/unhealthy lawn has tons of room for weeds to grow, so it becomes a field of dandelions. \n\n\n\n\n\nHealthy microbiome exposed to C. difficileUnhealthy microbiome (post-antibiotics) exposed to C. difficile\n\n\n\n\n\n\n\n\n\nConclusion\n\n\n\nAntibiotics don't just kill bacteria that cause infections; they can also kill "good" bacteria in your intestines. Now a perfect storm can occur where the only bacteria remaining are the more resistant type (e.g. C. difficile) and there is also more room for them to grow. This can unfortunately result in unchecked growth and infection.\n\n\n\nThis is why we try to avoid using antibiotics unless we really need them. If we do need antibiotics, we try to use narrow-spectrum antibiotics. Otherwise, if we use the big gun broad-spectrum antibiotics when they aren't required, we will be needlessly increasing the risk of C. difficile.