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Necrotizing fasciitis caused by group A streptococcus (GAS) is a life-threatening, rapidly progressing infection. At present, biofilm is not recognized as a potential problem in GAS necrotizing soft tissue infections (NSTI), as it is typically linked to chronic infections or associated with foreign devices. Here, we present a case of a previously healthy male presenting with NSTI caused by GAS. The infection persisted over 24 days, and the surgeon documented the presence of a "thick layer biofilm" in the fascia. Subsequent analysis of NSTI patient tissue biopsies prospectively included in a multicenter study revealed multiple areas of biofilm in 32% of the patients studied. Biopsies associated with biofilm formation were characterized by massive bacterial load, a pronounced inflammatory response, and clinical signs of more severe tissue involvement. In vitro infections of a human skin tissue model with GAS NSTI isolates also revealed multilayered fibrous biofilm structures, which were found to be under the control of the global Nra gene regulator. The finding of GAS biofilm formation in NSTIs emphasizes the urgent need for biofilm to be considered as a potential complicating microbiological feature of GAS NSTI and, consequently, emphasizes reconsideration of antibiotic treatment protocols.

Background Necrotizing soft-tissue infections (NSTI) are life-threatening conditions often caused by β-hemolytic streptococci, group A Streptococcus (GAS) in particular. Optimal treatment is contentious. The INFECT cohort includes the largest set of prospectively enrolled streptococcal NSTI cases to date. Methods From the INFECT cohort of 409 adults admitted with NSTI to 5 clinical centers in Scandinavia, patients culture-positive for GAS or Streptococcus dysgalactiae (SD) were selected. Risk factors were identified by comparison with a cohort of nonnecrotizing streptococcal cellulitis. The impact of baseline factors and treatment on 90-day mortality was explored using Lasso regression. Whole-genome sequencing of bacterial isolates was used for emm typing and virulence gene profiling. Results The 126 GAS NSTI cases and 27 cases caused by SD constituted 31% and 7% of the whole NSTI cohort, respectively. When comparing to nonnecrotizing streptococcal cellulitis, streptococcal NSTI was associated to blunt trauma, absence of preexisting skin lesions, and a lower body mass index. Septic shock was significantly more frequent in GAS (65%) compared to SD (41%) and polymicrobial, nonstreptococcal NSTI (46%). Age, male sex, septic shock, and no administration of intravenous immunoglobulin (IVIG) were among factors associated with 90-day mortality. Predominant emm types were emm1, emm3, and emm28 in GAS and stG62647 in SD. Conclusions Streptococcal NSTI was associated with several risk factors, including blunt trauma. Septic shock was more frequent in NSTI caused by GAS than in cases due to SD. Factors associated with mortality in GAS NSTI included age, septic shock, and no administration of IVIG.

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The study results do not support the use of HBOT as a treatment option in a severe attack of UC.