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A hypothetical bacterium swims among human intestinal contents until it finds a suitable location on the intestinal lining. It adheres to the intestinal lining using a feature that also protects it from phagocytes, bacteriophages, and dehydration. Fecal matter from a human in whose intestine this bacterium lives can spread the bacterium, even after being mixed with water and boiled. The bacterium is not susceptible to the penicillin family of antibiotics. It contains no plasmids and relatively little peptidoglycan.
Which of the following statements about the cell wall is most probable?
A) Its innermost layer is composed of a phospholipid bilayer.
B) After it has been subjected to Gram staining, the cell should remain purple.
C) It has an outer membrane of lipopolysaccharide.
D) It is mostly composed of a complex, cross-linked polysaccharide.

Question

Quizplus · Accepted Answer

The mention of lipopolysaccharide (LPS) in the outer membrane of the cell wall suggests that it is a Gram-negative bacterium. Gram-negative bacteria have a thin layer of peptidoglycan in their cell wall, surrounded by an outer membrane of LPS. This is the only option that accurately describes the composition of the cell wall. Option A is incorrect, as a phospholipid bilayer is a characteristic of the cell membrane, not the cell wall. Option B is incorrect, as Gram-negative bacteria should turn pink after Gram staining. Option D is incorrect, as this type of cell wall is typical of Gram-positive bacteria.

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