Macrophages mediate crucial innate immune responses via caspase-1-dependent 
processing and secretion of interleukin 1β (IL-1β) and IL-18. Although infection 
with wild-type Salmonella typhimurium is lethal to mice, we show here that a 
strain that persistently expresses flagellin was cleared by the cytosolic 
flagellin-detection pathway through the activation of caspase-1 by the NLRC4 
inflammasome; however, this clearance was independent of IL-1β and IL-18. 
Instead, caspase-1-induced pyroptotic cell death released bacteria from 
macrophages and exposed the bacteria to uptake and killing by reactive oxygen 
species in neutrophils. Similarly, activation of caspase-1 cleared unmanipulated 
Legionella pneumophila and Burkholderia thailandensis by cytokine-independent 
mechanisms. This demonstrates that activation of caspase-1 clears intracellular 
bacteria in vivo independently of IL-1β and IL-18 and establishes pyroptosis as 
an efficient mechanism of bacterial clearance by the innate immune system.