Characterising Post-mortem Bacterial Translocation Under Clinical Conditions Using 16S rRNA Gene Sequencing in Two Animal Models.

Lily Gates,Dagmar G Alber,Neil J Sebire,Nigel J Klein

doi:10.3389/fmicb.2021.649312

Lily Gates, Dagmar G Alber + Show 2 more

Open Access

https://doi.org/10.3389/fmicb.2021.649312

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Abstract

Sudden unexpected death in infancy (SUDI) is the sudden and unexpected death of an apparently healthy infant occurring within the first year of life where the cause is not immediately obvious. It is believed that a proportion of unexplained infant deaths are due to an infection that remains undiagnosed. The interpretation of post-mortem microbiology results is difficult due to the potential false-positives, a source of which is post-mortem bacterial translocation. Post-mortem bacterial translocation is the spread of viable bacteria from highly colonised sites to extra-intestinal tissues. We hypothesise that although post-mortem bacterial translocation occurs, when carcasses are kept under controlled routine clinical conditions it is not extensive and can be defined using 16S rRNA gene sequencing. With this knowledge, implementation of the 16S rRNA gene sequencing technique into routine clinical diagnostics would allow a more reliable retrospective diagnosis of ante-mortem infection. Therefore, the aim of this study was to establish the extent of post-mortem bacterial translocation in two animal models to establish a baseline sequencing signal for the post-mortem process. To do this we used 16S rRNA gene sequencing in two animal models over a 2 week period to investigate (1) the bacterial community succession in regions of high bacterial colonisation, and (2) the bacterial presence in visceral tissues routinely sampled during autopsy for microbiological investigation. We found no evidence for significant and consistent post-mortem bacterial translocation in the mouse model. Although bacteria were detected in tissues in the piglet model, we did not find significant and consistent evidence for post-mortem bacterial translocation from the gastrointestinal tract or nasal cavity. These data do not support the concept of significant post-mortem translocation as part of the normal post-mortem process.

Highlights

Sudden unexpected death in infancy (SUDI) is the sudden death of an apparently healthy infant occurring within the first year of life where the cause is not immediately obvious
At each time point from D0 to D10 Bifidobacteriaceae represented less than 1% of the total bacterial community
Our results demonstrate that significant and consistent PM bacterial translocation was not observed in the mouse model, shown by broad-range 16S rRNA gene sequencing and confirmed with more specific, bacteria-targeted quantitative PCR (qPCR)

Summary

Introduction

Sudden unexpected death in infancy (SUDI) is the sudden death of an apparently healthy infant occurring within the first year of life where the cause is not immediately obvious. Classical bacterial culture is the gold-standard method used to identify potential causative organisms as part of routine clinical autopsy investigation (Kennedy, 2016). These methods are associated with many limitations, such as an increased likelihood of identifying readily culturable bacteria (Yu et al, 2019), the inability to culture all bacterial species under laboratory conditions (Hiergeist et al, 2015; Overmann et al, 2017), long incubation periods (Ombelet et al, 2019), skilled persons or high-cost equipment for bacterial identification, and the curation of only qualitative results (Rhoads et al, 2012). The interpretation of PM microbiology results generated in this way proves difficult, in cases of SUDI where histological findings are often unclear (Pryce et al, 2011b; Palmiere et al, 2016)

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