Three hundred and twenty six bacterial isolates were used to
determine the specificity of the assay. These strains (Table 1)
included 232 Shigella isolates from clinical and food sources and
one control strain, S. flexneri 2457M, a genetically modified
version of wild-type S. flexneri 2457T harboring a cassette
conferring kanamycin resistance into the mxiC gene (Deer and
Lampel, 2010). Ninety-four non-Shigella species were also tested,
including several known to be genetically close to Shigella such as
E. coli (59 strains, including 49 EIEC isolates) and Salmonella
enterica (24 strains). The strains were grown overnight in Tryptic
Soy Broth (TSB) at 30 C to increase the probability that the
Shigella strains maintained the invasion plasmid (Schuch and
Maurelli, 1997).