Two autopsy cases of necrotizing soft-tissue infection in which the causative organism was inferred by 16S rRNA gene analysis

Necrotizing soft-tissue infection (NSTI) is a rapidly progressing, life-threatening disease that is difficult to diagnose based on clinical findings alone. NSTI often does not present with pus at the infection site, so it may not be suspected during an autopsy. Consequently, bacterial cultures are not performed, which hinders identification of the causative organism. In this study, we attempted to amplify the 16S ribosomal RNA (16S rRNA) gene (also referred to as 16S rDNA) from blood samples collected during forensic autopsies in two cases where death was suspected to be due to NSTI, as determined by postmortem histological examination. These samples had been stored frozen for up to 170 months. However, bacteriological testing was not performed at the time of autopsy because NSTI was not suspected. In one case, a 16S rRNA gene was amplified for Vibrio vulnificus, and in the other, for Streptococcus pyogenes (Group A Streptococcus). Based on the autopsy findings and laboratory results, it was determined that the NSTI caused by these bacteria was the most likely cause of death. These results suggest that amplifying bacterial 16S rRNA genes from frozen postmortem blood samples may help in future cases.