The human digestive tract is a jungle of different microorganisms ranging from fungi, bacteria, viruses to even helminths (worms). Some of these are commensal to the gut, meaning they are a normal part of our microbiome flora jungle, and are important for our optimal health. We have bacteria that digest nutrients from food we eat, and in turn produce vitamin B12 or vitamin K for us to absorb. On the other hand, there are bacteria that are opportunistic pathogens, such as H-pylori, or fungi such as Candida. These pathogens “take the opportunity” to proliferate (overgrow) when they get the chance.