Background: Group A streptococci (GAS) are known to cause serious invasive infections, but little is known about outcomes when patients with these infections are admitted to intensive care. We wanted to describe critically ill patients with severe sepsis or septic shock due to invasive GAS (iGAS) and compare them with other patients with severe sepsis or septic shock. Methods: Adult patients admitted to a general intensive care unit (ICU) in Sweden (2007-2019) were screened for severe sepsis or septic shock according to Sepsis 2 definition. Individuals with iGAS infection were identified. The outcome variables were mortality, days alive and free of vasopressors and invasive mechanical ventilation, maximum acute kidney injury score for creatinine, use of continuous renal replacement therapy and maximum Sequential Organ Failure Assessment score during the ICU stay. Age, Simplified Acute Physiology Score (SAPS 3) and iGAS were used as independent, explanatory variables in regression analysis. Cox regression was used for survival analyses. Results: iGAS was identified in 53 of 1021 (5.2%) patients. Patients with iGAS presented a lower median SAPS 3 score (62 [56-72]) vs 71 [61-81]), p < 0.001), had a higher frequency of cardiovascular cause of admission to the ICU (38 [72%] vs 145 [15%], p < 0.001) and had a higher median creatinine score (173 [100-311] vs 133 [86-208] μmol/L, p < 0.019). Of the GAS isolates, 50% were serotyped emm1/T1 and this group showed signs of more pronounced circulatory and renal failure than patients with non-emm1/T1 (p = 0.036 and p = 0.007, respectively). After correction for severity of illness (SAPS 3) and age, iGAS infection was associated with lower mortality risk (95% confidence interval (CI) of hazard ratio (HR) 0.204-0.746, p < 0.001). Morbidity analyses demonstrated that iGAS patients were more likely to develop renal failure. Conclusion: Critically ill patients with iGAS infection had a lower mortality risk but a higher degree of renal failure compared to similarly ill sepsis patients. emm1/T1 was found to be the most dominant serotype, and patients with emm1/T1 demonstrated more circulatory and renal failure than patients with other serotypes of iGAS.

Streptococcus pyogenes carrying M1 protein causes the severe and increasingly prevalent streptococcal toxic shock syndrome and necrotizing fasciitis. M1 protein is an important virulence factor of S. pyogenes and induces an inflammatory response in human monocytes. We wanted to investigate if purified M1 protein in solution could induce vascular NO production leading to vasopressor hyporesponsiveness. Rat aortic segments were incubated with M1 protein or LPS in vitro. M1 protein (10 microg mL) and LPS (1 ng mL) to a similar extent induced NO production and hyporesponsiveness to the vasoconstrictor phenylephrine. Immunogold electron microscopy demonstrated that M1 protein binds to Toll-like receptor 2 (TLR2) as well as TLR4 in mouse aorta but only to TLR2 in human omental artery. Incubation with M1 protein caused a reduction in the contractile response to phenylephrine in aortic segments from wild-type and TLR2-knockout but not from TLR4-knockout mice. In conclusion, M1 protein causes vascular NO production leading to hyporesponsiveness to vasopressors via a mechanism involving TLR, but the subtypes may be species dependent. M1 protein could contribute to the circulatory disturbances accompanying severe invasive streptococcal infections.

BackgroundStreptococcus pyogenes is a Gram positive bacterial species commonly involved in sepsis. Invasive strains express virulence factors such as the M1 protein. M1 protein forms complexes with fibrinogen leading to a cytokine storm in plasma contributing to the development of septic shock and organ failure. In experimental animals M1 protein causes vascular nitric oxide production and hyporesponsiveness to pressors, but it is not known whether it affects the human vascular wall.MethodsHuman omental arteries obtained during surgery were incubated in vitro with M1 protein or lipopolysaccharide (LPS) as positive control, with or without plasma. After 48 h, contractile response to noradrenaline was measured, and levels of nitrite/nitrate and the cytokines interleukin (IL)-1β, IL-6, IL-8, IL-10, and tumor necrosis factor (TNF)-α in the incubation medium were measured. A second set of arteries were incubated with or without main components of plasma (immunoglobulin G, albumin or fibrinogen), in the presence of M1 protein followed by cytokine measurement.ResultsArtery segments incubated with M1 protein and plasma contracted weaker in response to noradrenaline, and levels of IL-6 and IL-8 were significantly higher compared to after incubation with M1 protein alone. Incubation with M1 protein and fibrinogen resulted in elevated levels of IL-6 and IL-8, while incubation with M1 protein and albumin or immunoglobulin G did not affect the levels. Neither any of the other cytokines nor nitrite/nitrate was detected in the medium in any of the incubation conditions.ConclusionsThe study shows that M1 protein of Streptococcus pyogenes has a direct effect on the human vascular wall in the presence of plasma, demonstrated both as a diminished contractile response to noradrenaline and increased cytokine production. The effect of plasma was attributed to fibrinogen. The findings suggest that M1 protein contributes to the development of septic shock through impairment of the contractility of the vascular wall.