There are around 100 trillion bacteria in our guts, so it’s impossible to know the precise composition of anyone’s microbiome before they start a course of antibiotics, or after they finish. But modern gut testing can give us a good idea.
Research has revealed that antibiotics have the potential to decimate our gut bacteria. That means that the round you took for your sinus infection could have cut your gut flora down to one tenth of its previous level. Not by one tenth, to one tenth: that’s a 90 percent reduction (Source: NCBI).