Question 1

Which of the following best explains why Gram-negative bacteria are often more resistant to antibiotics than Gram-positive bacteria?

Accepted Answer

Their outer membrane contains porins and efflux pumps that limit antibiotic entry and actively expel drugs.

Question 2

A patient with cystic fibrosis develops a severe lung infection. Which virulence factor of Pseudomonas aeruginosa most contributes to its persistence in the thick mucus of the lungs?

Accepted Answer

Biofilm formation

Question 3

Which pigment produced by Pseudomonas aeruginosa is fluorescent under UV light and acts as a siderophore to scavenge iron?

Accepted Answer

Pyoverdine

Question 4

A microbiologist is culturing Haemophilus influenzae. Which medium should be used to provide the necessary growth factors?

Accepted Answer

Chocolate agar

Question 5

Which of the following best describes the mechanism by which Legionella pneumophila survives inside macrophages?

Accepted Answer

It uses a Type IV secretion system to block lysosome fusion, allowing replication in a vacuole.

Question 6

Which of the following is a distinguishing feature of Bordetella pertussis compared to other Gram-negative bacilli discussed?

Accepted Answer

It produces tracheal cytotoxin that damages ciliated cells.

Question 7

A hospital outbreak of infections is traced to a bacterium that forms blue-green pus in wounds and is highly resistant to antibiotics. Which of the following best explains its resistance?

Accepted Answer

It has efficient efflux pump systems and restrictive porins.

Question 8

Which of the following equations best represents the exponential growth of bacteria such as Pseudomonas aeruginosa under optimal conditions?

Accepted Answer

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

Question 9

Which of the following statements about Haemophilus influenzae is TRUE?

Accepted Answer

Encapsulated strains (especially type b) are more virulent and can cause meningitis in children.

Question 10

Which of the following best explains why Pseudomonas aeruginosa can grow in environments with soap residue?

Accepted Answer

It can metabolize unusual carbon sources and tolerates low moisture.

Question 11

A patient presents with pneumonia after using a contaminated hot tub. Which bacterium is most likely responsible, and what is its key intracellular survival strategy?

Accepted Answer

Legionella pneumophila; replication inside a vacuole by blocking lysosome fusion

Question 12

Which of the following is NOT a function of the fimbriae (pili) found on Gram-negative bacilli?

Accepted Answer

Motility through flagellar movement

Question 13

Which of the following best describes the role of siderophores such as pyoverdine in bacterial virulence?

Accepted Answer

They chelate iron from the host, promoting bacterial growth.

Question 14

Which of the following is the primary reason why Bordetella pertussis causes the characteristic 'whooping' cough?

Accepted Answer

Destruction of ciliated respiratory epithelial cells by tracheal cytotoxin

Question 15

Which of the following best explains why vaccination against Haemophilus influenzae type b (Hib) is effective in preventing invasive disease?

Accepted Answer

It induces antibodies against the type b capsule, preventing bacterial invasion.

Question 16

Which of the following is a common feature of enteric Gram-negative bacilli such as Escherichia coli, Salmonella, and Shigella?

Accepted Answer

They possess fimbriae for attachment and can act as opportunistic pathogens.

Question 17

A patient with a burn wound develops a greenish-blue pus and the infection is difficult to treat. Which pigment is most likely responsible for the color, and what is its additional function?

Accepted Answer

Pyocyanin; generates reactive oxygen species and damages host tissues

Question 18

Which of the following best describes the transmission route of Legionella pneumophila?

Accepted Answer

Inhalation of aerosols from contaminated water sources

Question 19

Which of the following equations would you use to calculate the number of bacteria after $$n$$ generations, starting with $$N_0$$ bacteria, assuming binary fission?

Accepted Answer

$$N = N_0$ 	imes 2^n$$

Gram-Negative Bacilli: Structure, Pathogenicity, and Clinical Relevance

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