A 59-year-old woman is brought to the emergency department with fever, skin flushing, and an altered level of consciousness. Her blood pressure is 50/20 mmHg, and her heart rate is 120/min despite receiving IV fluids. If blood cultures are positive for E. coli, which of the following bacterial factors is most directly responsible for this patient's current condition?

Question

A 59-year-old woman is brought to the emergency department with fever, skin flushing, and an altered level of consciousness.  Her blood pressure is 50/20 mmHg, and her heart rate is 120/min despite receiving IV fluids.  If blood cultures are positive for E. coli, which of the following bacterial factors is most directly responsible for this patient's current condition?

Quizplus · Accepted Answer

This patient has septic shock (ie, fluid-refractory hypotension in a patient with sepsis) as a result of the release of bacterial endotoxins into the bloodstream. Endotoxins are found in the outer membrane of Gram-negative bacteria (eg, E. coli), which is composed of lipopolysaccharide (LPS). LPS is released by destruction of the bacterial cell wall or during cell division. LPS is a very long, heat-stable molecule arranged into three regions: O antigen, core polysaccharide, and Lipid A. Lipid A is toxic to mammalian cells and acts as a virulence factor by inducing the release of endogenous pyrogens (eg, IL-1, prostaglandins) and inflammatory mediators (eg, TNFa, interferon) from activated macrophages. These cytokines cause the manifestations of septic shock: fever, hypotension, increased vascular permeability with third-spacing of fluids, and organ failure. (Choice A) E. coli strains can produce a capsule (eg, K-1 antigen) which provides a defense against phagocytosis by immune cells but does not directly contribute to the manifestations of septic shock. (Choice B) Fimbriae, or pili, allow bacteria to adhere to the target tissue and establish infection. Although Enterotoxigenic E. coli is an example of an organism that uses fimbriae, bacterial adhesion is not directly responsible for the manifestations of septic shock. (Choice C) Heat-stable exotoxin is one of the enterotoxins produced by Enterotoxigenic E. coli but is responsible for secretory diarrhea rather than the manifestations of septic shock. (Choice E) Although the O antigen is part of the lipopolysaccharide of a gram-negative bacteria and can be used for identification of different strains, it is not directly involved in the manifestations of septic shock. Educational objective: Gram-negative sepsis is caused by the release of lipopolysaccharides from bacterial cells during cell division or bacteriolysis. Lipid A is the toxic component of lipopolysaccharides and induces the widespread release of IL-1 and TNF-alpha from activated macrophages. These cytokines cause the signs and symptoms of septic shock (eg, fever, hypotension, organ dysfunction).

A 59-Year-Old Woman Is Brought to the Emergency Department with Fever