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Published on: July 15, 2011
Fungal DNA challenge in human STR typing of bone samples
Gayvelline C Calacal1, Maria Corazon A De Ungria
1DNA Analysis Laboratory, Natural Sciences Research Institute, University of the Philippines, Diliman, Quezon City, Philippines.
Abstract:
The present study focuses on possible cross-reaction of fungal DNA with human STR primers that may affect subsequent forensic DNA analysis of forensic samples. Specificity of human STR markers namely HUMAMEL, HUMCSF1PO, D8S306, HUMTH01, HUMvWA, HUMFES/FPS, HUMF13A01, HUMDHFRP2, HUMFGA and HUMTPOX was tested using DNA of 24 different filamentous fungal isolates obtained from exhumed bone samples. The specificity of these ten STR markers for human DNA was demonstrated. Presence of non-human DNA in five bone samples analyzed did not alter scoring of detected alleles. Notably, amplification was inhibited in the presence of a high proportion of fungal DNA compared to human DNA (1000 ng: 1 ng) in DNA mixture experiments. The results of the present study underscore the importance of carefully analyzing the presence of non-human biological contaminants that may affect DNA typing of environmentally challenged forensic samples to avoid spurious data interpretation.
Insights
Fungal DNA does not cross-react with human Short Tandem Repeat (STR) primers, ensuring accurate forensic DNA analysis. However, high fungal DNA concentrations can inhibit amplification, highlighting the need to assess non-human contaminants in forensic samples.
Area of Science:
- Forensic Science
- Molecular Biology
- Mycology
Background:
- Forensic DNA analysis relies on human Short Tandem Repeat (STR) markers.
- Environmental factors can introduce non-human DNA, potentially compromising sample integrity.
- Understanding potential cross-reactivity is crucial for reliable forensic investigations.
Purpose of the Study:
- To evaluate the specificity of ten human STR markers against fungal DNA.
- To determine if fungal DNA interferes with human STR profiling in forensic samples.
- To assess the impact of non-human DNA on STR allele interpretation.
Main Methods:
- Testing ten human STR markers (e.g., HUMAMEL, HUMCSF1PO) with DNA from 24 fungal isolates.
- Analyzing bone samples containing non-human DNA.
- Conducting DNA mixture experiments with varying ratios of human to fungal DNA.
Main Results:
- Human STR markers demonstrated specificity for human DNA, with no cross-reactivity observed with fungal DNA.
- The presence of non-human DNA did not affect the scoring of detected human alleles.
- Amplification inhibition occurred when fungal DNA significantly outnumbered human DNA (1000 ng: 1 ng).
Conclusions:
- Human STR markers are specific and reliable for forensic analysis, even with fungal presence.
- High levels of fungal DNA can inhibit PCR amplification, potentially leading to false negatives.
- Careful consideration of non-human biological contaminants is essential for accurate DNA typing of challenging forensic samples.
