Metagenomic Analysis reveals Importance of Anaerobes in Development and Clinical Outcome of Necrotizing Soft-tissue infections

BACKGROUND: Skin and soft-tissue infections can manifest in a variety of ways, ranging from a self-resolving abscess to a rapidly spreading necrotizing soft-tissue infection (NSTI). Based on culture data, the microbiology of both infections are similar, both involving Gram-positive cocci such as Staphylococcus species. This begs the question – why would different patients start with seemingly similar infections and end with drastically different clinical courses? One factor is the patient’s immune response, but it does not fully account for many NSTIs that occur in otherwise healthy individuals. We hypothesize that anaerobes, which are difficult to detect via culture and thus are under-detected, worsen the infection, favoring the NSTI pathology. Our objective in this study was to better understand the impact of anaerobes in NSTIs. METHODS: We enrolled adult patients that had been diagnosed either with NSTIs or abscesses. We collected samples of their infections via routine skin debridements or incision and drains, respectively. We then extracted DNA from each sample and sequenced the variable regions 1–2 of the 16S rRNA. The sequences were compared against an in house database and for species identification. RESULTS: From December 2011 to the present, we have collected 26 NSTI samples and 19 abscess samples. We found that a higher proportion of obligate anaerobes in the wound is correlated with increased BMI and mortality in NSTIs. The wound microbiomes of patients who died from their infections also seem to cluster together. Moreover, our preliminary data suggest that NSTIs may also have a higher proportion of obligate anaerobes and higher microbial diversity compared with abscess infections. Lastly, we noted significant disconcordance between data obtained by our institution clinical microbiology laboratory and our 16S data. CONCLUSION: The presence of obligate anaerobes, traditionally difficult to detect via culture, plays a significant role in the development and worsened clinical outcome of NSTIs. Their presence may be one of the determining factors that favor the NSTI pathology over the easily-treated abscess. If true, this should lead to more aggressive and comprehensive anaerobe coverage in NSTIs, especially in culture-negative infections. DISCLOSURES: All authors: No reported disclosures.