Bacterial transmigration as an indicator of time of death.

Time of death is difficult to evaluate in many forensic science situations. We have developed an animal model for assessing the time of death by evaluating the transmigration of normal microbiota through the wall of the small intestine. A segment of small intestine was removed from decapitated CF-1 mice ( Carnsworth Farms) and suspended in vitro in a beaker containing sterile phosphate-buffered saline. Bacterial transmigration was evaluated in this model over a three-day period at select temperatures (4, 25, and 37 degrees C) by microbiological cultures and scanning electron microscopy (SEM). Evidence of bacterial transmigration by SEM occurred within 2 to 3 h at 37 degrees C, 5 to 6 h at 25 degrees C, and 72 h at 4 degrees C. Analysis of the microbiological data indicated a differential flux of select bacterial and mycotic organisms. Staphylococcal species were the first organisms to be cultured from the suspending saline. These organisms are known to elaborate powerful protease enzymes that may play an important role in the degeneration of gut tissues. Coliform-type organisms and candida species were found at later times after death. The last major groups of bacteria to be identified were a variety of anaerobic species. This model may be adaptable to certain situations in human forensic pathology.