Colonization occurs when microorganisms live on or in a host organism but do not invade tissues or cause damage. Colonization refers to the presence of microorganisms which can cause infection, but not to the infection itself. Having these microorganisms present does increase the risk of infection if the right environment occurs.

When microorganisms find a commodious place to take up residence, they naturally begin to grow and multiply—this is known as colonization. This term has also given way to one of our favorite myths around probiotics.

Many people incorrectly believe that probiotics must colonize our gut and alter the composition of our microbiome to have an impact. This is not true—in fact, outside of cases like fecal transplants, most probiotics don’t colonize. The introduction of beneficial microbes that pass through our gastrointestinal tract can influence many factors of our health. We call these ‘Transient Microbes’.