The boiling method failed for the samples spiked with 102
Shigella cells/ml. A higher level of sensitivity was obtained for DNAs
prepared with the three commercial DNA extraction kits, but
because of the capacity limit of the DNeasy columns and PrepMan
Ultra reagent PCR inhibition, the InstaGene matrix appeared more
suited to process produce samples after enrichment. The low limit
of detection (LOD) of the multiplex assay for Shigella in produce is
higher than the LOD in real-time PCR (Deer and Lampel, 2010; Lin
et al., 2010); but in these two studies, the LOD was estimated from
spiked rinses from various produce types rather than from spiked
post-enrichment medium resulting in fewer competitive
microflora.