Passage
Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a bacterium responsible for causing foodborne illnesses. EHEC virulence, or the ability to cause disease, is acquired through quorum sensing, a form of bacterial cell-cell communication dependent on population density. EHEC O157:H7 bacteria monitor population density by detecting changes in the concentration of autoinducer-3 (AI-3) , an extracellular signaling molecule secreted by many bacterial species. AI-3 generally acts on neighboring bacteria to activate the genes on the enterocyte effacement (LEE) locus. These genes code for type III secretion proteins (EspA, EspB, EspD, Tir) , which promote entry of Shiga-like toxins secreted by EHEC into host intestinal epithelial cells. This ultimately leads to cell death, lesions, and symptoms such as bloody diarrhea and abdominal cramps.It has been reported that a mutation in S-ribosylhomocysteine lyase (LuxS) , an enzyme involved in quorum sensing, may result in diminished production of AI-3. However, researchers predict that certain peptide hormones can activate LEE gene transcription in the LuxS. To test this hypothesis, mutant EHEC bacteria deficient in LuxS (LuxS⁻) were cultured and separately exposed to the hormones epinephrine (E) , norepinephrine (NE) , gastrin (G) , and secretin (S) at 37°C. Total RNA was extracted from the treated bacterial cultures, and LEE mRNA was quantified (Figure 1) .
Figure 1 Concentration of LEE mRNA in mutant LuxS⁻ bacteria supplemented with purified peptide hormones (Note: C = control.) Western blot was performed to compare the presence and concentration of type III secretion proteins from wild-type (WT) , LuxS⁻, and LuxS⁻ cultured in preconditioned media (PCM) . PCM was generated by culturing uninfected intestinal epithelial cells in growth media for 24 hours. After 24 hours, the cells were removed and the PCM was used to supplement the growth of LuxS⁻ bacteria.
Figure 2 Western blot results of type III secretion proteins isolated from WT, mutant LuxS⁻, and LuxS⁻ in PCM
-Which of the following is most likely to be found within the cell membranes of intestinal epithelial cells?

Question

Passage
Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is a bacterium responsible for causing foodborne illnesses. EHEC virulence, or the ability to cause disease, is acquired through quorum sensing, a form of bacterial cell-cell communication dependent on population density. EHEC O157:H7 bacteria monitor population density by detecting changes in the concentration of autoinducer-3 (AI-3) , an extracellular signaling molecule secreted by many bacterial species. AI-3 generally acts on neighboring bacteria to activate the genes on the enterocyte effacement (LEE) locus. These genes code for type III secretion proteins (EspA, EspB, EspD, Tir) , which promote entry of Shiga-like toxins secreted by EHEC into host intestinal epithelial cells. This ultimately leads to cell death, lesions, and symptoms such as bloody diarrhea and abdominal cramps.It has been reported that a mutation in S-ribosylhomocysteine lyase (LuxS) , an enzyme involved in quorum sensing, may result in diminished production of AI-3. However, researchers predict that certain peptide hormones can activate LEE gene transcription in the LuxS. To test this hypothesis, mutant EHEC bacteria deficient in LuxS (LuxS⁻) were cultured and separately exposed to the hormones epinephrine (E) , norepinephrine (NE) , gastrin (G) , and secretin (S) at 37°C. Total RNA was extracted from the treated bacterial cultures, and LEE mRNA was quantified (Figure 1) .

Figure 1 Concentration of LEE mRNA in mutant LuxS⁻ bacteria supplemented with purified peptide hormones (Note: C = control.) Western blot was performed to compare the presence and concentration of type III secretion proteins from wild-type (WT) , LuxS⁻, and LuxS⁻ cultured in preconditioned media (PCM) . PCM was generated by culturing uninfected intestinal epithelial cells in growth media for 24 hours. After 24 hours, the cells were removed and the PCM was used to supplement the growth of LuxS⁻ bacteria.

Figure 2 Western blot results of type III secretion proteins isolated from WT, mutant LuxS⁻, and LuxS⁻ in PCM
-Which of the following is most likely to be found within the cell membranes of intestinal epithelial cells?

Quizplus · Accepted Answer

11ecba2d_0f53_88f9_a3bf_53cdfc9dee1d_MD0008_00 The cell membrane is a phospholipid bilayer that separates the interior of the cell (the intracellular space) from the external environment (the extracellular space). The two phospholipid layers are oriented such that the hydrophobic tails of the phospholipids in the inner and outer layers are in contact with each other, leaving the hydrophilic head groups in contact with either the intracellular or the extracellular fluid environment. The cell membrane is described by the fluid mosaic model as a nonrigid (fluid) phospholipid bilayer through which diverse proteins are scattered (the mosaic) and are able to migrate laterally. In addition to phospholipids, animal cell plasma membranes also contain cholesterol, glycolipids (lipids with attached sugar groups), glycoproteins (proteins with attached sugar groups), and other proteins. Cholesterol, which is found in eukaryotic but not prokaryotic cell membranes, functions to regulate the fluidity of the bilayer. Due to their unique structure, cholesterol molecules decrease fluidity at higher temperatures and increase fluidity at lower temperatures. As eukaryotic cells, intestinal epithelial cell membranes contain cholesterol. (Choice A) All cells, eukaryotic and prokaryotic, have a plasma membrane, but some cell types are surrounded by an additional enveloping layer known as the cell wall. Unlike the plasma membrane, the cell wall is a rigid structure that defines the shape of the cell it surrounds and provides added protection. Animal cells, including intestinal epithelial cells, do not have cell walls. However, nearly all prokaryotic cells have a cell wall. The major structural component of the bacterial cell wall is peptidoglycan, a polymer of sugars and short polypeptides. (Choice C) Cytoskeletal filaments are found in the cytoplasm of cells and can interact directly with various components of the cell membrane (eg, by anchoring membrane proteins in place). However, they are not themselves part of the plasma membrane. (Choice D) Cellulose, a polysaccharide, is the primary component of the cell wall in plant cells. Cellulose is not found in the membranes of animal cells. Educational objective: The plasma membrane is a fluid lipid bilayer that contains a diverse array of proteins scattered throughout. Certain cell types have a cell wall surrounding their plasma membrane; however, animal cells do not have a cell wall. The primary component of bacterial cell walls is peptidoglycan.

Passage Enterohemorrhagic Escherichia Coli (EHEC) O157:H7 Is a Bacterium Responsible for for Causing