Total DNA was isolated from each probiotic food supplement by a
commercially available DNA extraction kit (QIAamp DNA Mini Kit —
Qiagen, Milan, Italy). The isolated DNA was resuspended in 200μl of
elution buffer and stored at−20 °C until use as a DNA template in the
PCR reactions. Table 3 shows PCR cycling conditions used for the
detection of the microbial species. Most species-specific PCR primers,
generally located in the 16S–23S rRNA encoding region, were selected
on the basis of the microbial species listed on the labels of the different
products (Table 4). The PCR reactions were carried out in a
thermal cycler (M.J. Research, PTC100, Watertown, USA), and PCR
products were analyzed by using 1% agarose gel electrophoresis. The
gels were stained with ethidium bromide and viewed by using a UV
transluminator.