Inflammatory responses and histopathological changes in a mouse model of Staphylococcus aureus-induced bloodstream infections.

INTRODUCTION

Staphylococcus aureus-induced bloodstream infections (BSIs) remain a prevalent clinical challenge and the underlying pathogenesis is still poorly understood. The aim of this study was to investigate the inflammatory responses and histopathological changes in BSIs in mice.

METHODOLOGY

Male C57BL/6 mice were inoculated with S. aureus intravenously to induce BSIs. The survival rate, weight loss, and murine sepsis scores (MSS) were monitored in BSI and phosphate-buffered saline (PBS) control mice. Blood samples and tissue homogenates were plated on agar plates to determine the bacterial burden. Inflammatory proteins and cytokines were determined by enzyme-linked immunosorbent assay (ELISA) kits. Histopathologic changes were assessed by pathological inflammation score (PIS) and macroscopic and microscopic examinations.

RESULTS

BSI mice induced by 4.5 × 108 CFU/mL S. aureus showed ~70% survival rate, higher sepsis scores, significantly decreased body weight, elevated levels of white blood cell (WBC) counts, C-reactive protein (CRP), procalcitonin (PCT), interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α. Prominent correlations were found between elevated CRP and PCT levels as well as among IL-1β, IL-6, and TNF-α. Pathological changes and higher PIS were also observed in BSI mice.

CONCLUSIONS

Our results demonstrate that inflammatory proteins (PCT and CRP) and cytokines (IL-6, IL-1β and TNF-α) play an important role in the inflammatory responses and histopathological changes in S. aureus-induced BSIs.