Two partial DNA sequences retrieved from the National Center for Biotechnology Information database. (a) GenBank Locus GQ247740, a 293-base long signature sequence for B. burgdorferi 16S rDNA. TEC1 (left) and LD2 (right) PCR primer sites underlined. (b) GenBank Locus FJ948170, a 287-base long sequence of 16S rDNA for numerous environmental bacteria. TEC1 and LD2 primer sites underlined. Note 6 mismatched bases printed in red bold face. X------ = 231 bases in a sequence specific and unique for B. burgdorferi 16S rDNA. X = 225 bases in a sequence nonspecific for environmental bacterial 16S rDNA. 000000 = 6 slots with no nucleotide bases. In the absence of a fully matched B. burgdorferi DNA, the PCR primers may bind to a partially matched non-target bacterial DNA templates which are not infrequently present in normal human blood. Only DNA sequencing can distinguish the 287 base-pair PCR amplicon of a common environmental bacterial 16S rDNA from a 293-base B. burgdorferi 16S rDNA.