1-7 Bacterial Growth and Function

Question 1

What is a flagellum, and how is it significant to bacterial pathogenesis?

Answer 1

A flagellum is a simple, stiff, corkscrew-shaped structure composed of long flagellin polymers that protrudes from the cell wall. It rotates to propel a bacterium forward.

NOTE: Bacterial flagella are NOT the same as eukaryotic flagella, which are complex, whip-like structures that burn ATP and wave side to side.

Question 2

How are bacterial ribosomes significant to bacterial pathogenesis?

Answer 2

Due to chemical differences that differentiate them from eukaryotic ribosomes (80S), bacterial ribosomes (70S) are excellent targets for drugs.

• Aminoglycosides can attack the small subunit to interfere with initiation and accuracy.
• Tetracyclines intefere with the transfer of activated amino acids to ribosomes
• Macrolids attack the rRNA of the large subunit, affecting elongation

Question 3

How are endospores significant to bacterial pathogenesis?

Answer 3

Spore-forming bacteria (e.g., Bacillus and Clostridium) can survive extreme environmental conditions (e.g., temperatures, dehydration, antiseptics, antibiotics) by compressing their genome and a minimal entourage of macromolecules into a thick, spherical coat. When nutrients and water are plentiful again, the spore can “unpack” into its normal bacterial form and resume normal metabolism and reproduction.

Question 4

What is the bacterial growth curve?

Answer 4

• Lag phase: bacteria sense new environment and upregulate (liquid culture = clear)
• Log phase: rapid cell division with exponential growth curve (liquid culture = lightly cloudy)
• Stationary phase: growth rate = death rate due to nutrient depletion, waste accumulation (liquid culture = very cloudy)
• Death phase: most remaining bacteria die due to waste accumulation (liquid culture = sediment on the bottom, lightly cloudy with chunks in the middle, pellicle on top)

Question 5

Why are some bacteria obligate aerobes?

Answer 5

They lack superoxide dismutase and/or catalase enzymes, and they also lack pathways to regenerate coenzymes that have become oxidized. In other words, they cannot detoxify oxygen radicals.

Question 6

How does fermentation differ from the electron transport pathway?

Answer 6

• Less efficient to generate ATP
• Breaks down sugars instead of oxygen
• Produces organic acids as waste products (usu. lactic and/or pyruvic acid). These can be used to narrow the differential; they can be detected with pH indicators, which reveal the bacterium’s ability to ferment the provided sugar

Question 7

What is quorum sensing?

Answer 7

A bacterial ability to sense their population density and adjust their gene expression accordingly. It can allow bacteria to conserve energy and coordinate their “attack.”

ex) biofilms, pathogens secreting virulence factor (to reach effective concentration)