Reacción a "Genital microbiome could help identify sexual offenders"

The study shows that changes in the composition of the vaginal and penile microbiome can occur before and after a sexual act. However, given the small sample size and the variability of cases found, no conclusive general pattern is detected. In my opinion, the study should have made a more careful analysis of the variability in the sampling, since, although 10 replicates were taken, only one was sequenced per case, which does not allow us to establish what basic variability we could expect in the sampling. In the same way, more controls of samples would be needed, taken at similar intervals without there being a [sexual] relationship, in order to know what the expected fluctuations could be in its absence.

The chosen sequencing methodology (16S gene amplicons) allows us to identify the species of bacteria with a fair degree of resolution, but does not ensure that we can establish that they are clonal, as would be expected from a transmission. The state of the art for establishing clonality is based on massive genomic DNA sequencing techniques (shotgun). Furthermore, the presence of the same 16S variants in two different people does not imply direct transmission and, as the couples share housing and habits, dual colonization cannot be ruled out.

Regarding the possible forensic application, I believe that the data allow us to glimpse future possibilities, but they do not provide evidence that it is possible, for example, to identify the aggressor from the possible variants detected in a victim. It is foreseeable that, unlike this study, samples taken shortly before the attack will not be available. Obtaining DNA from the aggressor himself in any remains found in the victim or crime scene would provide a more precise and direct identification. One advantage that the microbiome could have over human DNA is the persistence over time of clones transmitted from aggressor to victim, something that is not investigated here.