Multiplex PCR for detection of SPI-7 and tviB. The presence of the tviB gene in the viaB locus is shown by a band at about 0.8 kb, and the absence of the SPI-7 region is shown by a band at about 1.5 kb. The aroC products are at 0.6 kb. Lanes: Vi-positive controls Ty2 (lane 1), SARB63 (lane 16), and CT18 (lane 24); Vi-positive clinical isolates BL13807, BL15339, and BL13510 (lanes 2 to 4, respectively); Vi agglutination-negative Salmonella isolates BL9282 (lane 5), BL14907 (lane 6), BL13843 (lane 7), BL9283 (lane 8), BL12035 (lane 9), BL3081 (lane 10), BA788 (lane 11), BL4426 (lane 12), BL6886 (lane 13), BL6397 (lane 14), BL6583 (lane 15), BL2934 (lane 22), BL13994 (lane 17), BL9737 (lane 18), BL1838 (lane 20), and BL2580 (lane 21); Vi negative controls Salmonella serovar Paratyphi A BL11161 (lane 19) and SARB64 (lane 23).