by Karen Schwarzberg, Mike Gur­ney, and Nikos Gur­field — Typ­i­cally, when one thinks about the com­men­sal bac­te­ria liv­ing with us, what comes to mind are the ben­e­fits they pro­vide by aid­ing in food me­tab­o­lism, pro­duc­ing vi­t­a­mins, and pre­vent­ing col­o­niza­tion by in­vad­ing path­o­genic bac­te­ria.