Long-term control of Salmonella after transient T3SS-2 inhibition

Anti-virulence approaches are promising alternatives for traditional antibiotics to control bacterial infections. Several inhibitors show impressive activities in animal infection models, but the relative contribution of specific virulence inhibition vs off-target effects on both the bacteria and host remain unclear. Here, we developed Salmonella with switchable virulence by putting the type 3 secretion system-2 (T3SS-2) which is essential for systemic virulence, under the control of doxycycline. In infected mice given low-dose doxycycline in drinking water, the strain showed normal fitness and virulence. Doxycycline withdrawal shut down T3SS-2, arrested Salmonella replication and resolved disease symptoms. After ten days of T3SS-2 inhibition, reintroducing doxycycline restored replication, but bacterial loads remained stable, indicating strengthened host immunity. These effects were comparable to treatment with fluoroquinolone antibiotics, a highly effective therapy for human systemic salmonellosis. Thus, selective T3SS-2 inhibition may offer a suitable alternative for controlling invasive Salmonella infections.