Direct-STR typing from presumptively-tested and untreated body fluids

Body fluids provide key pieces of information for a forensic investigation. However, sometimes only a small amount of body fluids is found and/or DNA are also degraded by environmental factors at the crime scene. In extreme cases, a forensic analyst may have to decide whether to perform a presumptive test on the stains or proceed straightaway to DNA profiling, which could be wasteful for non-biological stains. Additionally, due to the inefficient DNA extraction process, the amount of DNA may not be enough for STR typing, especially if parts of the evidence had been subjected to presumptive testing. To overcome these problems, we developed a direct PCR method for STR profiling of stains (blood, saliva, and semen) that had been subjected to presumptive tests and also those that had not undergone presumptive tests. Using the optimized protocols, 86 of 90 untreated samples (95.6%) resulted in a full DNA profile. For presumptively-tested samples, both the type of presumptive test used and the surfaces where the stains are deposited affected the quality of the STR profiles. With blood, we obtained full STR profiles from 88% of samples tested with luminol and 78% with Hemastix. The acid phosphatase test for semen and Phadebas test for saliva resulted in full STR profiles from 85% and 73% of samples, respectively. Different substrates also affected the resulting STR profiles, but there was no clear trend based on absorbency or texture. The interactions of types of body fluids, presumptive tests, and substrates must be considered together. Our direct PCR protocol can be used to detect DNA even with 6 months-old biological samples. The benefits of the developed protocol include increasing amount of DNA obtained from evidence, decreasing chances of DNA contamination from complex or lengthy extraction steps, using minimal sample amount for analysis, and most importantly, improving STR profiles. Also, the process could save analysis time and cost due to the omission of DNA extraction and quantification. Our developed method could be beneficial to cases with limited stains available, as forensic analysts can perform indirect presumptive testing on the suspected stains and direct PCR could be carried out from the filter paper used, thus leaving the original stain for subsequent DNA extraction or re-analysis.