The intestinal microbiota could protect against HIV infection. At the 30th Conference on Retroviruses and Opportunistic Infections (CROI) last week, a group of scientists from Duke University presented data showing a preventive effect of two bacteria from the Lachnospiraceae family, the species Clostridium immunis and Ruminococcus gnavus against HIV. These microorganisms strongly inhibited HIV replication in vitro through the metabolic pathway of tryptophan and the aryl hydrocarbon receptor.