Analysis of mixed sequencing chromatograms and its application in direct 16S rRNA gene sequencing of polymicrobial samples.

Investigation of clinical samples by direct 16S rRNA gene sequencing provides the possibility to detect nonviable bacteria and bacteria with special growth requirements. This approach has been particularly valuable for the diagnosis of patients who have received antibiotics prior to sample collection. In specimens containing more than one bacterium, direct sequencing gives mixed chromatograms that complicate further interpretation. We designed an algorithm able to analyze these ambiguous chromatograms and implemented it as a Web-based service. The algorithm contains both a new base-calling procedure and a new database search procedure. 16S rRNA gene sequencing was performed on polybacterial suspensions prepared in the laboratory. The computer program identified all bacteria correctly to the species level in 23 out of 23 samples containing two different bacteria. For samples containing three different bacteria, correct identification to the species level was achieved for three out of five and to the genus level for five out of five.