The human microbiota is a mixture of microorganisms that are maintained in symbiosis with the host. However, sometimes this symbiosis goes awry, causing pathogen outgrowth and disease. For example, periodically, Staphylococcus aureus emerges from the skin-resident microbiome as a disease-causing pathogen. Boldock et al. show that such irruptions can be mediated by particulate peptidoglycan (PTG) expressed from the cell walls of nonpathogenic (commensal) skin bacteria. PTG promotes S. aureus survival in innate immune cells such as macrophages and neutrophils, and this facilitates systemic infection. This phenomenon is not mediated by established receptor pathways such as Nod1, Nod2, Myd88, or the NLPR3 inflammasome.
Nat. Microbiol. 3, 881 (2018).