Virulence determinants in California S. sonnei isolates. Virulence determinants in California S. sonnei isolates. Virulence determinants: stx1A, Shiga toxin 1, subunit A, variant a; stx1B, Shiga toxin 1, subunit B, variant a; sigA, Shigella IgA-like protease homolog; gad, glutamate decarboxylase; ipaH9.8, invasion plasmid antigen; senB, plasmid-encoded enterotoxin; prfB, P-related fimbriae regulatory gene; lpfA, long polar fimbriae; celb, endonuclease colicin E2; ipaD, invasion protein S. flexneri; virF, VirF transcriptional activator; iss, increased serum survival; sat, secreted autotransporter toxin. Varvara K. Kozyreva et al. mSphere 2016; doi:10.1128/mSphere.00344-16