Salmonella biofilms program innate immunity for persistence in Caenorhabditis elegans

Significance Salmonella resides as an intracellular pathogen in eukaryotic hosts and causes diarrhea or typhoid fever. In a small but alarming proportion of infected humans, Salmonella exists asymptomatically as biofilms, a basis for long-term disease transmission. Although Salmonella biofilms have been observed in chronically infected mice, mechanisms underlying why and how such multicellular aggregates are formed in vivo remain poorly understood. We exposed optically transparent Caenorhabditis elegans to Salmonella and observed the progression of infection in intestines from free-living cells to static aggregates. We discovered that a secreted toxin is down-regulated when Salmonella forms biofilms, leading to an adaptive advantage in chronic infections. Hence, Salmonella biofilms enable dormancy to prolong in vivo existence.