First of all, 99% of all gut bacteria is anaerobic.
Over 99% of the bacteria in the gut are anaerobes, but in the cecum, aerobic bacteria reach high densities.
Second, almost every single species of bacteria, yeast or archaea that lives inside of your gut is beneficial one way or another.
Those species that are not beneficial, will most likely only pass through.
When you take Antibiotics
or some other drugs, it creates a serious imbalance in the microbiome, and that imbalance is the problem, cause after that imbalance it is very difficult to get those 1000 species back into previous balance.
That opens the door for all bad bacteria.
Some people, who have taken some very bad Antibiotics
or any Antibiotics
for too long or too many times .. for those people it is even impossible to return to the previous balance, cause intestines get damaged forever, and it is impossible to restore those 1000 species back to balance.
Candida species are just few out of 500 - 1000 species that can colonize your intestines.
Anything you take by your mouth can affect gut flora, one way or another.
ALways start with one single drop of anything, and increase slowly, watch for negative effects.
If you take Hydrogen-Peroxid orally, it will definitively affect microflora of your mouth, and some upper digestive tract.
Will it reach the colon?
Will it affect bacteria in Colon?
It is individual.
There is no simple answer to that but to try it yourself and report results.
Your own experience will be different from the experience of other people.