Amplifications included 30 cycles (94 °C for 30 s, 58 °C for 1 min and 72 °C

for 2 min 30 s), followed by a final extension step at 72 °C for 10 min. Template S. Typhi and S. Typhimurium chromosomal DNA was prepared as described previously (Santiviago et al., 2001). Primers sopD21 (GTGTGGCTGTTCCAGAATGTGCTG) and sopD22 selleckchem (CCGTTGCTAAACTGCCGTTTGCTTA) were used to amplify a fragment of 1800 bp. For S. Typhimurium 14028s mutagenesis, primers sopD23W (ATGCCAGTTACGTTAAGTTTTGGTAATCGTCATAACTATGTGTAGGCTGGAGCTGCTTCG) and sopD24W (TATATAAGCATATTGCGACAACTCGACTTTTCACTTATACATATGAATATCCTCCTTAG) were used to amplify the aph- and cat-resistance cassette from pKD3 and pKD4, respectively (Datsenko screening assay & Wanner, 2000). Letters in italics highlight primer sequences that annealed with both resistance cassettes. All primers were designed on the basis of the reported sequence of S. Typhimurium LT2 sopD2 (AE006468.1). The sopD2 PCR product was cloned directly in the pCC1 vector according to the manufacturer’s instructions (CopyControl™ PCR Cloning Kit, Epicentre) to yield the plasmid pNT007. The presence of the gene and its promoter region in the plasmid was confirmed by PCR amplification and restriction

endonuclease analyses. The cloned PCR product was sequenced to ensure that it did not harbor any mutation (data not show). sopD2 pseudogene sequencing was performed by Macrogen Corp. (Rockville, MD) using S. Typhi chromosomal DNA prepared as described (Santiviago et al., 2001) and pNT007 Avelestat (AZD9668) previously isolated using the Wizard miniprep kit (Promega). To generate the chromosomal deletion of sopD2, a ‘one-step inactivation’ protocol was performed (Datsenko & Wanner, 2000). Following mutagenesis, aph- and cat-resistance cassettes were removed by FLP-mediated recombination. To measure bacterial invasion, the method described by Lissner et al. (1983) and modified by Contreras et al. (1997) was used. Briefly, HEp-2 monolayers were grown at 37 °C in a 5% CO2/95% air mixture in RPMIFS (RPMI medium supplemented with 10% fetal bovine serum pretreated for 30 min at 60 °C). Bacterial

strains were grown anaerobically to mid-exponential phase and then harvested by centrifugation before infection of the confluent HEp-2 monolayers in 96-well microtiter plates at a multiplicity of infection of 100 : 1. After incubation for 1 h to allow bacterial entry into cells, monolayers were washed twice with phosphate-buffered saline (PBS), and 100 μL of RPMI containing gentamicin (200 μg mL−1) was added to each well. The plates were then incubated for 2 h to kill any remaining extracellular bacteria. For strains carrying vectors, the medium was supplemented with chloramphenicol throughout the assay. The medium was removed and cells were washed twice with PBS. The cells were then lysed with sodium deoxycholate (0.5% w/v in PBS).