FIG. 4.

Amplification controls. Agarose gel electrophoresis of PCR products amplified with 16S rRNA gene primers 516F and 13R (about 874 bp). E. coli was inoculated into blood culture medium containing human blood and processed by one of the four listed digestion and purification protocols. In the first five lanes, the processed DNA was diluted in sterile, UV-irradiated water as indicated, and 5 μl of DNA target were added to a 50-μl PCR mixture along with 1 μl of additional B. pertussis DNA. Lane Neg, unprocessed, sterile water (negative control); and Lane Pos, 1 μl (79 ng) of B. pertussis DNA (positive control) subjected to PCR. A 1-kb DNA ladder is present in the last lane.