An Enterobacteriaceae Bloom in Aging Animals is Restrained by the Gut Microbiome

The gut microbiome plays important roles in host function and health.Core microbiomes have been described for different species, and imbalances in their composition, known as dysbiosis, are associated with pathology.Changes in the gut microbiome and dysbiosis are common in aging, possibly due to multitissue deterioration, which includes metabolic shifts, dysregulated immunity, and disrupted epithelial barriers.However, the characteristics of these changes, as reported in different studies, are varied and sometimes conflicting.Using clonal populations of Caenorhabditis elegans to highlight trends shared among individuals, we employed 16S rRNA gene sequencing, colony-forming unit counts, and fluorescent imaging, identifying an Enterobacteriaceae bloom as a common denominator in aging animals.Experiments using Enterobacter hormaechei, a representative commensal, suggested that the Enterobacteriaceae bloom was facilitated by a decline in Sma/BMP immune signaling in aging animals and demonstrated its potential for exacerbating infection susceptibility.However, such detrimental effects were contextdependent and mitigated by competition with commensal communities, highlighting the latter as determinants of healthy versus unhealthy aging, depending on their ability to restrain opportunistic pathobionts.