Relationship between cell number and Ct.

<p>Log-linear relationships between the copy number of pathogen-specific sequence and Ct_pathogen and between the copy number of the human-specific sequence and Ct_human. (A) <i>S. pneumoniae</i>, <i>H. influenzae</i>, <i>Pseudomonas</i> spp., or <i>M. catarrhalis</i> was suspended in sputum. DNA was then purified from the suspension, and the target sequences specific to each organism were amplified by PCR. A log-linear relationship indicates that the sputum does not contain molecules that inhibit isolation of DNA or exponential amplification by PCR. Experiments were done in triplicate. A bar indicates standard deviation. (B) Human genomic DNA isolated from sputum was serially diluted, and a DNA sequence in the human SFTPC gene (arbitrarily selected from human genes, of which sequence is specific to human by BLAST search of GenBank database; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0024474#pone-0024474-t002" target="_blank"><b>Table 2</b></a>) was amplified. A log-linear relationship indicates that the sputum does not contain molecules that inhibit isolation of DNA or exponential amplification by PCR.