Obligate anaerobes are abundant in human necrotizing soft tissue infection samples - a metagenomics analysis.

Necrotizing soft tissue infections (NSTIs) are associated with high morbidity and mortality and are increasing in incidence. Proper identification of the microbial causes of NSTIs is a crucial step in diagnosis and treatment, but the majority of data collected are culture based, which is biased against fastidious organisms, including obligate anaerobes. The goal of this study was to address this gap in knowledge by characterizing NSTI microbial communities through molecular diagnostics. We performed 16S rRNA sequencing on human NSTI samples and identified five genera most commonly found in NSTIs (Prevotella, Bacteroides, Peptoniphilus, Porphyromonas, and Enterococcus). We found that a >70% contribution of obligate anaerobes to the bacterial population distribution was associated with NSTI mortality, and that NSTI samples, from both survivors and non-survivors, had an increased relative abundance of gram negative bacteria compared to those of abscess patients. Based on our data, we conclude that obligate anaerobes are abundant in NSTIs and a high relative abundance of anaerobes is associated with a worse outcome. We recommend increasing anaerobe antibiotic coverage during the treatment of NSTIs even when anaerobes are not found by traditional clinical microbiology methods, and especially when there is a clinical suspicion for anaerobe involvement.