How to find homologous epitopes in human-gut microbiome

Question

[MOD]

Hello, I am doing a research project and since I'm new in bioinformatics, databases and this stuff i will consider any help.

So, I've found an epitope in a protein that is expressed in humans. I wonder how can I blast this specific epitope (which database should I use and how) in order to find out if there is any homology of it in proteins of the human gut microbiome... For cross-reactivity purposes.

Thank you!