Question 1

Which of the following best defines a biofilm?

Accepted Answer

An aggregate of microorganisms in which cells are stuck to each other and/or to a surface, often embedded in a self-produced matrix of extracellular polymeric substance (EPS).

Question 2

What is the primary function of the extracellular polymeric substance (EPS) in a biofilm?

Accepted Answer

To embed and protect the microbial community, facilitating adhesion to surfaces and resistance to environmental stress.

Question 3

Which of the following statements about quorum sensing in biofilms is correct?

Accepted Answer

Quorum sensing is the process by which bacteria communicate and coordinate behavior based on cell density using signaling molecules called inducers.

Question 4

Why are bacteria in biofilms generally more resistant to antibiotics than planktonic (free-living) bacteria?

Accepted Answer

The EPS matrix physically blocks antibiotics and slows their diffusion, and the close proximity of cells facilitates the exchange of resistance genes.

Question 5

A patient with cystic fibrosis develops a chronic lung infection. Which property of Pseudomonas aeruginosa biofilms most contributes to the persistence of this infection?

Accepted Answer

Biofilms allow the bacteria to evade the immune system and resist antibiotic treatment.

Question 6

Which of the following best describes the role of water currents in biofilm structure, as shown in Figure 21.1?

Accepted Answer

Water currents move through pillars and channels in the biofilm, bringing nutrients and removing wastes.

Question 7

Which laboratory procedure is used to visualize biofilm growth on microscope slides?

Accepted Answer

Simple staining with methylene blue after air-drying and heat-fixing the slide.

Question 8

In the context of biofilm formation, what is the significance of the following equation for cell density and inducer concentration?

$$C_{inducer} \propto N_{cells}$$

where $$C_{inducer} is $$the concentration of inducer and $$N_{cells} is $$the number of cells.

Accepted Answer

As the number of cells increases, the concentration of inducer increases, promoting coordinated gene expression.

Question 9

Which of the following is a real-world example of a biofilm causing a medical problem?

Accepted Answer

Formation of dental plaque leading to cavities.

Question 10

A new catheter design uses pressure to remove biofilms. What is the most likely mechanism by which this works?

Accepted Answer

Pressure expands a channel, physically dislodging the biofilm from the catheter surface.

Question 11

Which of the following best explains why multiple species of bacteria and fungi can coexist in a biofilm?

Accepted Answer

The EPS matrix provides a structured environment with micro-niches, allowing different species to thrive together.

Question 12

Which step is essential before staining a biofilm sample with methylene blue?

Accepted Answer

Air-drying and heat-fixing the slide to adhere the biofilm to the glass.

Question 13

Which of the following is NOT a characteristic of biofilms?

Accepted Answer

They are composed of free-floating, planktonic cells only.

Question 14

Why is it important to leave a few millimeters of each slide exposed when incubating slides in a hay infusion for biofilm formation?

Accepted Answer

To allow oxygen exchange and facilitate microbial attachment at the air-liquid interface.

Question 15

Which of the following best describes the process of simple staining with methylene blue?

Accepted Answer

Applying methylene blue to a heat-fixed smear, waiting for 1 minute, rinsing, and viewing under oil immersion.

Question 16

Which historical figure was the first to visualize and describe bacteria, which he called 'animalcules,' from dental plaque?

Accepted Answer

Van Leeuwenhoek

Question 17

Which of the following best explains why biofilms are important in clinical medicine?

Accepted Answer

Biofilms can form on medical devices, making infections more persistent and harder to treat.

Question 18

Which of the following is a correct sequence for preparing a biofilm slide for microscopic observation?

Accepted Answer

Collect slide, air-dry, heat-fix, stain with methylene blue, observe under oil immersion.

Question 19

Which of the following best describes the relationship between biofilm formation and quorum sensing?

Accepted Answer

Quorum sensing triggers gene expression changes that promote the production of EPS and biofilm formation when cell density is high.

Biofilms: Structure, Function, and Clinical Importance

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