Hydrogen Sulfide and Substance P Levels in Patients with Escherichia coli and Klebsiella pneumoniae Bacteraemia.

Hydrogen sulfide (H 2 S) and substance P (SP) are known from animal models and in vitro studies as proinflammatory mediators. In this study, peripheral blood concentrations of H 2 S and SP were measured in patients with Escherichia coli or Klebsiella pneumoniae bacteraemia. Fifty patients were recruited from general wards at Christchurch Hospital, during 2020-2021. Samples from age- and sex-matched healthy subjects previously recruited as controls for studies of cardiovascular disease were used as controls. The concentrations of H 2 S were higher than controls on day 0, day 1, and day 2, and SP was higher than controls on all 4 days. The concentrations of H 2 S were highest on day 0, whereas SP concentrations were higher on day 2 than other days. Interleukin-6 and C-reactive protein were significantly higher on day 0 and day 1, respectively. The concentrations of H 2 S and SP did not differ between 15 non-septic (SIRS 0-1) and the 35 septic subjects (SIRS ≥ 2). Substance P concentrations were higher in subjects with abdominal infection than urinary tract infections on day 0 ( p = 0.0002) and day 1 ( p = 0.0091). In conclusion, the peak H 2 S concentrations precede the SP peak in patients with Gram-negative bacteraemia, but this response varies with the site of infection.