Postmortem alterations of bacterial localization.

Abstract

Localization of bacteria in mammalian gastrointestinal tracts by electron microscopy has yielded much information on our understanding of intimate host-microbial interactions, but because of difficulties in obtaining human tissue, the human host-microbial interactions have not been well studied. In this report, an attempt was made to ascertain the feasibility of using gastrointestinal tissues obtained at autopsy. A rat model was used to produce samples that would simulate conditions that autopsy samples might undergo. Rats, left at room temperature for 1 hr and then refrigerated at 2C for time intervals up to 24 hours after death were autopsied and samples from the stomach, ileum and cecum were removed and processed for light and scanning microscopy. Tissues were fixed in buffered glutaraldehyde, postfixed in buffered osmium tetroxide, dehydrated in an ethanol series, critical point dried, coated with gold-palladium and examined. Keratinized murine stomachs showed little or no changes in the localization of the gram-positive layer of bacteria over 24 hours. However, major changes were noted in the ileum and colon with the ileum showing the most dislocation of the flora. Colonic tissues were altered by invading bacteria although some regions had a relatively normal appearing host-flora relationship. Slow cooling rates of the gastrointestinal tracts were implicated as a major cause for alterations in bacterial localization. The data predict that studies of normal microbial location with human autopsy samples will be best pursued on keratinized tissue.