Hemoglobin and Escherichia coli, a lethal intraperitoneal combination.

Area of Science:

• Immunology
• Microbiology
• Pathophysiology

Background:

• Hemolysis, the breakdown of red blood cells, releases free hemoglobin into circulation.
• The role of free hemoglobin in modulating bacterial infections, particularly in the peritoneal cavity, remains incompletely understood.

Purpose of the Study:

• To investigate the lethal effects of Escherichia coli (E. coli) when administered with free hemoglobin in a murine model.
• To elucidate the mechanism by which free hemoglobin influences E. coli peritonitis and host response.

Main Methods:

• Mice were injected intraperitoneally with E. coli suspended in various solutions: free hemoglobin, intact erythrocytes, whole blood, plasma, or saline.
• Bacterial growth, peritoneal absorption, and host inflammatory responses were assessed.
• Fractionation of lysates was performed to isolate the effects of hemoglobin versus other proteins.

Main Results:

• E. coli suspended in free hemoglobin or hemoglobin lysate was lethal, while suspensions in intact erythrocytes, whole blood, plasma, or saline were not.
• Rapid E. coli proliferation (overwhelming growth within 12 hours) and ineffective polymorphonuclear leukocyte response were observed in lethal infections.
• Free hemoglobin was identified as the sole component promoting lethal infection, independent of bacterial virulence or host resistance.

Conclusions:

• Free hemoglobin plays a critical role in promoting lethal E. coli peritonitis by inhibiting peritoneal absorption and creating an exudate that supports bacterial growth.
• The lethal outcome is attributed to intoxication from bacterial endotoxins, facilitated by hemoglobin's unique effects.
• These findings highlight the significance of free hemoglobin in scenarios involving both hemolysis and infection, such as peritonitis.