Development and application of a multiplex PCR system for drowning diagnosis.

In recent years, the DNA detection of drowning-related diatoms, cyanobacteria, and aeromonas has gradually attracted interest from forensic scientists. In this study, we described the validation and application of a novel multiplex PCR system. This system integrated 12 fluorescently labelled primers designed to amplify specific genes of diatoms, cyanobacteria, and aeromonas. The specificity studies demonstrated that this multiplex PCR system could detect nine species of diatom, seven species of cyanobacteria, and five species of aeromonas, all of which were drowning-related and widely distributed in various water circumstance of southern China. The sensitivity studies indicated that the limit concentration of template DNA was 0.0125 ng. Besides, this multiplex PCR system had good performance in sizing precision and stability, but it is not suitable for degraded DNA samples. The application into forensic casework showed that all the tissue samples from ten nondrowning cases showed negative results, and the positive rates of lung, liver, kidney, and water samples from 30 drowning bodies were 100, 86.7, 90, and 100%, respectively. Combined with results of diatom tests of MD-VF-Auto SEM method, this multiplex PCR system could help rule out nondrowning bodies and provide extra evidences to support drowning diagnosis, especially for those cases with few diatoms observed. It is expected that this multiplex PCR system has great potential for forensic drowning diagnosis.

SYBR Green real-time qPCR method: Diagnose drowning more rapidly and accurately.

In the field of drowning research, the method of diatom morphology has been most applied to determine whether the cause of death is drowning. However, the characteristics of complex operation, high level of professional knowledge drive us to propose a new method. Here, based on the common phytoplankton in water(such as diatoms and Aeromonas), aiming at the rbcL, 23 S, NIES, rPOD, Hly and preprotoxin aerolysin gene, we designed 6 pairs of specific primers and applied SYBR Green real-time qPCR(RT-qPCR) method to detect phytoplankton in the Pearl River Basin of Guangdong Province, China, so as to achieve the purpose of diagnosing drowning. After the experimental verification of the corresponding algae species and the standard strains of bacteria, as well as the verification of tissue samples (lung, liver and kidney) of 56 cases( 40 drowning cases and 16 non-drowning cases), we found that these primers were of great accuracy and tedious laboratory work of diatom test was reduced. Based on the advantages of high throughput, short period and high sensitivity, this RT-qPCR method is expected to diagnose drowning more rapidly and accurately.

A novel approach for the forensic diagnosis of drowning by microbiological analysis with next-generation sequencing and unweighted UniFrac-based PCoA.

The diagnosis of drowning is one of the major challenges in forensic practice, especially when the corpse is in a state of decomposition. Novel indicators of drowning are desired in the field of forensic medicine. In the past decade, aquatic bacteria have attracted great attention from forensic experts because they can easily enter the blood circulation with drowning medium, and some of them can proliferate in the corpse. Recently, the advent of next-generation sequencing (NGS) has created new opportunities to efficiently analyze whole microbial communities and has catalyzed the development of forensic microbiology. We presumed that NGS could be a potential method for diagnosing drowning. In the present study, we verified this hypothesis by fundamental experiments in drowned and postmortem-submersed rat models. Our study revealed that detecting the bacterial communities with NGS and processing the data in a transparent way with unweighted UniFrac-based principal coordinates analysis (PCoA) could clearly discriminate the skin, lung, blood, and liver specimens of the drowning group and postmortem submersion group. Furthermore, the acquired information could be used to identify new cases. Taken together, these results suggest that we could build a microbial database of drowned and postmortem-submersed victims by NGS and subsequently use a bioinformatic method to diagnose drowning in future forensic practice.