Effect of ozone disinfection on forensic STR profiling

While good laboratory practice in a forensic lab minimises the chance of infection of laboratory personnel, in certain cases, possible contamination of pieces of evidence with highly contagious pathogens might call for additional precautions. The number of potential disinfection methods that might be suitable for forensic genetics are surprisingly limited. First and foremost, the ideal technique should not inhibit DNA amplification, it should be effective against a host of pathogens, and it should be applicable on porous surfaces. We examined ozone treatment on extracted DNA samples and mock casework samples. Ozone-treated and control specimens were amplified with Qiagen Investigator ESSplex SE QS kit. Detected allele counts were compared between the treated and untreated sample groups. Following disinfection, concentration of ozone-treated DNA was about half of the control samples, but full STR profiles were recovered. In the case of mock casework samples (disposable surgical masks), there was no significant difference (p = 0.513) between the detected allele counts of control and ozone-treated samples. Sampling location of surgical masks (earloop, nosepiece) showed a statistically significant difference (p = 0.011), though. Comparing the effect of contributors on STR profiling, a significant difference (p = 0.001) was observed, which could be explained with the differences between individuals including shedding capacity, head size or shape. According to our pilot study, ozone treatment does not encumber the routine forensic DNA analysis, the sampling position or the contributor affected the allele counts more than the ozone treatment.