Samples spiked with 10 times less Shigella (requiring 10 or 15
doublings during enrichment whether one cell is present in 1 g or
in 25 g of produce, respectively) (Table 4), showed the three ex-
pected amplification products in some samples only. The Shigella
DNA was too diluted in the DNA samples prepared by boiling and
showed amplification only for themulticopy virulence gene ipaH at
best (Fig. 4).