Question

Which of the following is FALSE regarding Bacterial Endotoxins?

	a.	They can cause Fever and Hemorrhagic Shock
	b.	They are secreted by the cell
	c.	Examples of bacteria that produce them include Clostridium tetani and Bacillus anthracis.
	d.	The bacteria are typically found in soil

Which of the following is true regarding Gram (+) and a Gram (-) bacteria?

	a.	The Gram (-) have a thick layer of peptidoglycan on the surface of the cell
	b.	The Gram (+) have a cell wall and Gram (-) do not have a cell wall
	c.	The Gram (+) have a peptidoglycan layer that is sandwiched with a layer of liposaccharides on the surface
	d.	The Gram (+) have a thick layer of peptidoglycan on the surface of the cell

Answer 1

1. Bacterial endotoxins : Endotoxins are toxins released by bacteria. Endotoxins are also called Lipopolysaccharide (LPS) are derived from outer membrane of Gram negative bacteria. Lipid component Lipid A of Lipopolysaccharide is associated with toxicity of endotoxins. Endotoxins are heat stable and liberated only on cell lysis or death of bacteria.

The endotoxins are pyrogens, the pyrogens are fever inducing substances produced by bacteria. Endotoxins released from bacteria initiate host inflammatory response. It leads to increased cellular immune response. The inflammatory response is mediated by interleukin, cytokines, tumor necrosis factors, etc. The endotoxins may enter to blood and causes fever, nausea and aseptic shock.

Endotoxins are present almost everywhere in environment. In humans mostly present in digestive system.

Escherichia coli, Klebsiella, Proteus, Pseudomonas, Shigella are some enterotoxin producing bacteria.

False statement is 'c' Examples of bacteria that produce endotoxins are Clostridium tetani and Bacillus anthracis. Both theses are exotoxin producing bacteria.

2. The bacterial species are distnigushed into two main groups based on its cell wall structure and composition as Gram Positive and Gram negative bacteria by Gram staining.

The main distinguishing feature is the thickness of peptidoglycan and presence or absence of outer lipid layer. Gram positive bacteria have thick peptidoglycan layer but lack an outer lipid layer while Gram negative bacteria have a thin peptidoglycan layer covered with a outer lipid layer.

The thick peptidoglycan layer of Gram positive bacteria retain the primary crystal violet during staining and prevent from decolorisation. So cell appears in purple color. But in gram negative bacteria due to thin peptidoglycan layer primary stain crystal violet is decolourised by ethanol and take-up the color of counter stain Safranin and appears red.

Both Gram positive and Gram negative bacteria have cell wall. Gram positive bacteria is single layered while gram negative have double layered cell wall.

d. The Gram (+) have thick peptidoglycan layer on the surface of cell. Is only true statement.