Secreted antigen A peptidoglycan hydrolase is essential forEnterococcus faeciumcell separation and priming of immune checkpoint inhibitor therapy

Enterococcus faeciumis a microbiota species in humans that can modulate host immunity¹, but has also acquired antibiotic resistance and is a major cause of hospital-associated infections². Notably, diverse strains ofE. faeciumproduce SagA, a highly conserved peptidoglycan hydrolase that is sufficient to promote intestinal immunity^3–5and immune checkpoint inhibitor antitumor activity⁶. However, the functions of SagA inE. faeciumwere unknown. Here we report that deletion ofsagAimpairedE. faeciumgrowth and resulted in bulged and clustered enterococci due to defective peptidoglycan cleavage and cell separation. Moreover, ΔsagAshowed increased antibiotic sensitivity, yielded lower levels of active muropeptides, displayed reduced activation of the peptidoglycan pattern-recognition receptor NOD2, and failed to promote cancer immunotherapy. Importantly, plasmid-based expression of SagA, but not its catalytically-inactive mutant, restored ΔsagAgrowth, production of active muropeptides and NOD2 activation. SagA is therefore essential forE. faeciumgrowth, stress resistance and activation of host immunity.