Salmonella persisters undermine host immune defences during antibiotic treatment

Many bacterial infections are hard to treat and tend to relapse, possibly due to the presence of antibiotic-tolerant persisters that are considered dormant cells when bacteria are grown in laboratory medium. Non-growing persisters also form following uptake of Salmonella by macrophages but their nature is little understood. Here we show that Salmonella persisters arising during macrophage infection maintain an active state. Persisters reprogram macrophages by means of effectors secreted by the SPI-2 Type 3 Secretion System (T3SS), thereby dampening pro-inflammatory innate immune responses and inducing anti-inflammatory macrophage polarisation. Reprogramming allows non-growing Salmonella to survive for extended periods in their host. Persisters undermining the host immune defences might confer an advantage to the pathogen during relapse once the antibiotic pressure is relieved. Transcriptome profiling of macrophages/Salmonella in distinct subpopulations by dual RNA-Seq