Table 1. Commensal bacterial species that confer protection against pathogens.

Commensal	Pathogen	Mechanism	Reference
Staphylococcus lugdunensis	Staphylococcus aureus	Peptide antibiotic with bactericidal activity	7
Enterococcus faecalis with pPD1 plasmid	Vancomycin-resistant Enterococcus	Plasmid-encoded bacteriocin that inhibits pathogen growth	6
Bacillus thuringiensis	Clostridium difficile	Bacteriocin with bactericidal activity	87
Escherichia coli strain Nissle 1917	Salmonella typhimurium	Microcins with antimicrobial activity	8
Clostridium scidens	C. difficile	Conversion of primary to secondary bile acids which inhibit pathogen growth	4
Ruminococcus obeum	Vibrio cholerae	Quorum-sensing signals that interfere with pathogen gene expression	11
E. coli strains HS and Nissle 1917	E. coli O157:H7	Competition for carbohydrates	15
E. coli, Bacteroides thetaiotaomicron	Citrobacter rodentium	Competition for carbohydrates	16
E. coli strain Nissle 1917	S. typhimurium	Competition for iron	86
B. thetaiotaomicron	Candida albicans	LL-37 antimicrobial peptide induction	32
Bifidobacterium	E. coli O157:H7	Inhibition of Shiga toxin dissemination	33
Lactobacillus reuteri	C. albicans	Induction of type 3 innate lymphoid cells expansion and interleukin 22 production through tryptophan conversion to an aryl hydrocarbon receptor ligand	46
Segmented filamentous bacterium	C. rodentium	Induction of T helper 17 cells differentiation and subsequent expression of antimicrobial peptides	53
E. coli	S. typhimurium	Systemic induction of IgG	69