Question 1

Which structure is responsible for motility in most flagellated bacteria, and is recognized by the vertebrate innate immune system via TLR-5?

Accepted Answer

Flagellin

Question 2

A mutant strain of Vibrio cholerae lacking its polar flagellum would most likely show which phenotype in a host?

Accepted Answer

Decreased ability to reach the intestinal epithelium

Question 3

E. coli uses a 'random walk' model for chemotaxis. What happens when E. coli senses it is moving away from an attractant?

Accepted Answer

It tumbles more frequently to change direction

Question 4

Which equation best describes the probability $$P of a $$bacterium moving toward an attractant in a chemotaxis experiment, given $$n$$ runs and $$m$$ tumbles?

Accepted Answer

$$P = \frac{n}{n+m}$$

Question 5

Which of the following is a major reason why Listeria monocytogenes is a concern for pregnant patients?

Accepted Answer

It can grow at refrigeration temperatures and cross the placenta

Question 6

Listeria monocytogenes uses actin-based motility for cell-to-cell spread. What is the main advantage of this mechanism?

Accepted Answer

Rapid spread without exposure to the humoral immune system

Question 7

Which of the following statements about Gram-positive Listeria is TRUE?

Accepted Answer

They can invade and live within cells to avoid the host’s immune system.

Question 8

Which structure is primarily responsible for the initial loose attachment of E. coli to host cells?

Accepted Answer

Fimbriae (pili)

Question 9

A soft agar motility test is performed on three bacterial cultures. Tube B shows a thin line of growth only along the stab line. What does this indicate?

Accepted Answer

The bacteria are non-motile

Question 10

Which of the following is NOT a type of taxis observed in bacteria?

Accepted Answer

Electrotaxis

Question 11

Gram-negative bacteria can attach to surfaces via their _________.

Accepted Answer

Fimbriae

Question 12

Which equation best represents the rate $$R of $$bacterial colonization given $$A ($$adhesion rate) and $$C ($$colonization efficiency)?

Accepted Answer

$$R = A 	imes C$$

Question 13

Which bacterial structure is most likely to be downregulated in invasive pathogens once inside the host to avoid immune detection?

Accepted Answer

Flagellin

Question 14

A patient presents with symptoms of meningitis after consuming contaminated soft cheese. Which pathogen is most likely responsible, and what unique property allows it to cause disease even when food is refrigerated?

Accepted Answer

Listeria monocytogenes; psychrophilic growth

Question 15

Which of the following best describes the two-step attachment process of pathogenic E. coli?

Accepted Answer

Loose attachment via pili, followed by tight attachment via afimbrial adhesins

Question 16

Which equation would you use to calculate the number of bacteria $$N$$ adhering to a surface after $$t$$ hours, given an initial population $$N_0$$ and adhesion rate constant $$k$$?

Accepted Answer

$$N = N_0$ e$$^{kt}$$

Question 17

Which bacterial property is most important for colonization of mucosal surfaces, which are constantly washed by fluids?

Accepted Answer

Ability to adhere to mucosal cells

Question 18

Which of the following is a specific example of a bacterium using actin-based motility for cell-to-cell spread?

Accepted Answer

Listeria monocytogenes

Question 19

Which equation best describes the relationship between the number of flagella $$F$$ and the probability $$P of E. $$coli swimming in a straight line?

Accepted Answer

$$P = \frac{F_{CCW}}{F_{total}}$$

lecture 11

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