Determining Postmortem Interval by Comparing Intestinal Microbial Ratios over Various Temperatures.

摘要

Postmortem interval (PMI) is used in forensic science to assist in solving crimes. Reliable methods for determining PMI that can be applied to every death investigation are needed, and the study of microbial growth in the body after death may be one additional approach to satisfy this need. This study used a mouse model to determine cecal bacterial colony forming unit (CFU) ratios of three prominent intestinal bacterial species over five days postmortem in an attempt to establish baseline postmortem microbial trends for future use in determining PMI. Additionally, the CFU changes over time when the mice were kept at 4°C, ambient room temperature, and ambient outdoor temperature were compared to determine the effect of different environments on microbial ratios.;The three bacteria analyzed for this investigation were Lactobacillus spp., Enterococcus spp., and E. coli. E. coli was not present on any of the media plated and therefore determined to not be useful in determining PMI with microbial samples from the cecum of mice. Lactobacillus spp. and Enterococcus spp. were quantified from all the mice and CFUs along with their ratios were analyzed from each temperature. The ANOVA summary p values for comparison of ratios among all the time points within a specific environment were 0.557, 0.0002, and 0.0078 for 4°C, room temperature, and outdoors respectively. The p values <0.05 indicated that there were significant differences between some of the time points within that environment. Notably, the most significant change in the bacterial ratio occurred between 24 and 48 hours from mice kept at room temperature. When comparing all three environments, the hottest environment experienced the greatest ratio increase over time while the coldest environment experienced the least ratio change. When comparing ratios for a specific time point between the three different environments, four significant differences were observed and they were for PMIs greater than 24 hours. While few significant differences among the environments were observed, the data analysis showed that microbial ratios are useful in determining if a mouse body left at room temperature has been deceased for less than or greater than 48 hours. The results of this study show that further investigation of postmortem microbial changes needs to be explored in order to accurately predict PMI in this mouse model.