Fatal Polymicrobial Peritonitis Caused by Klebsiella variicola and Phytobacter massiliensis Identified by 16S rRNA Gene Sequencing: An Autopsy Case Report

Acute peritonitis is a life-threatening condition that, if left untreated, can rapidly progress to death owing to intra-abdominal sepsis. Here, we report an autopsy case of a 46-year-old Uzbek man who had experienced abdominal pain for about a month but died without timely medical intervention due to barriers to accessing care associated with his undocumented status. Autopsy revealed more than 1,600 mL of purulent ascites in the peritoneal cavity and localized purulent collection in the omentum. Culture of ascitic fluid collected at autopsy yielded bacterial growth, and subsequent 16S rRNA gene sequencing identified <i>Klebsiella variicola</i>, an emerging pathogen frequently misidentified as <i>K. pneumoniae</i> and associated with higher mortality in bloodstream infections, together with <i>Phytobacter massiliensis</i> (formerly <i>Metakosakonia massiliensis</i>), a recently reclassified taxon rarely reported as a cause of human intra-abdominal infection. This case highlights the forensic value of molecular diagnostics for accurate pathogen identification in postmortem investigations, with social barriers contributing to delayed presentation, which allows the infection to progress to a fatal outcome.