Unlike humans, adult mice with intact microbiota are resistant to gastrointestinal colonization with Candida albicans. In Nature Medicine, Koh and colleagues demonstrate that in mice, commensal anaerobic bacteria are critical for maintaining resistance to colonization with C. albicans. Treatment with penicillin, which depletes an aerobic bacteria, particularly Bacteriodetes and clostridial Firmicutes, induces colonization with C. albicans in adult mice. Recolonization with individual anaerobes (Blautia producta or Bacteroides thetaiotamicron) is sufficient to induce resistance to C. albicans, but recolonization with Bacteroides fragilis or Lactobacillus species is not. Colonization with Bacteroides thetaiotaomicron or Brachycybe producta increases expression of the transcription factor HIF-1α and the antimicrobial peptide CRAMP (an ortholog of human LL-37, known to have anti–C. albicans activity) in the mouse colon. HIF-1α and CRAMP are required for resistance to C. albicans in antibiotic-treated mice but not in untreated mice, which suggests redundant immunological pathways of resistance.

Nat. Med. (8 June 2015) doi:10.1038/nm.3871