Invasion and cytotoxicity of S . Typhimurium and S . Enteritidis for porcine alveolar macrophages. Panel A, invasion of the wild-type S. Typhimurium (wt) and isogenic ΔSPI1 mutant, and S. Enteritidis (wt) and isogenic ΔSPI1, sipA, hilA and sipB mutants into porcine alveolar macrophages 4 h post infection. Panel B, cytotoxicity of S. Typhimurium, S. Enteritidis and their isogenic mutants for porcine alveolar macrophage 24 h post infection. Controls included LDH released from non-infected PAMs, PAMS exposed to LPS, tissue culture medium, and PAMs lysed with 1% Triton X-100. * significantly different at p < 0.05 when t-test compared with appropriate wild-type strain.