Question 1

Which experimental approach would best determine if a candidate protein from Streptococcus pneumoniae is involved in adherence to lung epithelium?

Accepted Answer

Knockout the gene encoding the protein and assess bacterial adherence to epithelial cells in vitro.

Question 2

The term 'mannose sensitive fimbriae' refers to which property of certain bacterial fimbriae?

Accepted Answer

Fimbriae that mediate adherence to host cells and whose binding is inhibited by mannose.

Question 3

Where are non-fimbrial adhesins typically localized in Gram-positive and Gram-negative bacteria, and how do they differ in their attachment to the bacterial cell wall?

Accepted Answer

Gram-positive: covalently attached to peptidoglycan; Gram-negative: associated with outer membrane proteins.

Question 4

What is the function of the type III secretion system (T3SS) in pathogenic bacteria?

Accepted Answer

To inject effector proteins directly into host cells, manipulating host cell processes.

Question 5

Which of the following best describes the tissue tropism of a type III secretion system?

Accepted Answer

It is determined by the specificity of effector proteins for host cell receptors.

Question 6

During infection, what distinguishes invasive pathogens from non-invasive pathogens?

Accepted Answer

Invasive pathogens penetrate and spread within host tissues, while non-invasive pathogens remain localized.

Question 7

Listeria monocytogenes is a non-flagellated bacterium that uses actin-polymerization for cell-to-cell spread. What would be the consequence if Listeria lost its ability to polymerize actin?

Accepted Answer

It would be unable to spread from cell to cell and would remain confined to the initial infected cell.

Question 8

Streptococcus pyogenes possesses a capsule made of hyaluronic acid. How does this capsule help the bacterium evade the host immune system?

Accepted Answer

By mimicking host connective tissue components, making it less recognizable to immune cells.

Question 9

Which of the following pathogens also possesses a capsule composed of sialic acid?

Accepted Answer

Neisseria meningitidis

Question 10

What is the function and location of the M-protein in Streptococcus pyogenes?

Accepted Answer

It is a surface protein that inhibits phagocytosis and is located on the bacterial cell wall.

Question 11

For which purpose does Streptococcus pyogenes produce a C5a peptidase?

Accepted Answer

To degrade the complement component C5a and prevent recruitment of phagocytes.

Question 12

Streptococcus dysgalactiae produces a protein called protein G. What is its function?

Accepted Answer

It binds to the Fc region of IgG, interfering with opsonization.

Question 13

You want to isolate antibodies from a complex protein mixture, such as human serum. Which method would be most effective?

Accepted Answer

Affinity chromatography using protein A or protein G as the ligand.

Question 14

Homologous recombination involves the exchange of genetic material between similar DNA sequences. If the identical segments are in opposite orientation, what is the likely outcome?

Accepted Answer

An inversion of the intervening DNA segment.

Question 15

Which equation best describes the rate of bacterial growth during the exponential phase?

Accepted Answer

$$N_t = N_0$ e$$^{\mu t}$$

Question 16

A patient is infected with a bacterium that produces diphtheria toxin. How many elongation factors within a eukaryotic cell can be inactivated by a single subunit A of diphtheria toxin?

Accepted Answer

One molecule of elongation factor 2 (EF-2) per toxin subunit A.

Question 17

Which of the following best explains why some bacteria are resistant to beta-lactam antibiotics?

Accepted Answer

They produce beta-lactamase enzymes that hydrolyze the beta-lactam ring.

Question 18

Which of the following is a real-world example of a pathogen using actin-based motility for cell-to-cell spread?

Accepted Answer

Listeria monocytogenes moving through host cells by polymerizing host actin.

Question 19

Which of the following best describes the role of protein A in Staphylococcus aureus?

Accepted Answer

It binds to the Fc region of IgG, preventing effective opsonization.

Med mic Ex 3

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