Human identification through analysis of the salivary microbiome

Human identification has played a prominent role in forensic science for the past two decades and will continue to do so. The development of techniques to exploit samples, which cannot be satisfactorily analysed at present, is driving the field. High-throughput sequencing techniques have been available for a few years however there are very few examples of their application in forensic science. This study investigates the potential for bacteria found in the salivary microbiome to be used in a new method for human identification. Two different targets (16S RNA and rpoB) were chosen to maximise coverage of the salivary microbiome and when combined, they increase the power of identification. Paired-end Illumina high-throughput sequencing was used to analyse the bacterial composition of saliva from two different people at four different time points (t=0 and t=28 days and then one year later at t=0 and t=28 days). Five major phyla dominate the samples: Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes and Fusobacteria. Streptococcus, a firmicute, is one of the most abundant genera found in saliva and targeting Streptococcus rpoB has enabled a deeper characterisation of the different streptococci species otherwise impossible with 16S rRNA alone. We have observed that samples from the same person group together regardless of time of sampling. However, samples taken one month apart group closer together than those taken one year apart. The results indicate that it is possible to distinguish two people using the bacteria found in their saliva.