Differences in circulating levels of non-classical monocytes and associated caspase 1 activation during Staphylococcus aureus and Escherichia coli bacteremia.

Non-classical monocytes show increased caspase-1 activation and intermediate/non-classical monocyte expansion in patients with Escherichia coli bacteremia, unlike Staphylococcus aureus bacteremia.

• Why it matters: Innate immune signatures during bloodstream infection are inconsistently linked to the causative pathogen, limiting biomarker development and interpretation of disease severity effects.
• What they did: In a prospective cohort of monomicrobial bacteremia patients, peripheral blood myeloid subsets were profiled by flow cytometry and caspase-1 activation was measured as an inflammasome surrogate.
• The result: Myeloid subset frequencies and caspase-1 activation differed by sepsis status, but the E. coli versus S. aureus differences were primarily attributable to the infecting bacteria; eosinophil counts and caspase-1 activation may help distinguish bacterial BSI from viral infections.

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