Question 1

Which of the following best describes why *Escherichia coli* is considered a normal member of the human colon microbiota but can cause disease when found in contaminated food or other body sites?

Accepted Answer

Disease depends on host tissue damage, site, dose, virulence, and host resistance, not just microbial presence.

Question 2

Which of the following is an example of a cellular pathogen?

Accepted Answer

Bacterium

Question 3

Why are most microbes considered beneficial or harmless to humans and the environment?

Accepted Answer

Microbes decompose organic matter, recycle nutrients, and contribute to processes like photosynthesis and nitrogen fixation.

Question 4

Which of the following best explains how normal microbiota can both protect the host and sometimes contribute to disease?

Accepted Answer

They compete with pathogens for space and nutrients but can become opportunistic pathogens if the host is compromised.

Question 5

Which of the following would provide the strongest evidence that a change in the human microbiome causes a specific disease?

Accepted Answer

A controlled experiment where altering the microbiome leads to disease in a healthy host.

Question 6

Why are biofilm-associated infections often more difficult to treat than infections caused by planktonic (free-floating) bacteria?

Accepted Answer

Biofilms protect microbes from antibiotics and immune responses due to their extracellular matrix.

Question 7

Which of the following is a medically significant risk associated with biofilm formation?

Accepted Answer

Biofilms on catheters or implants can seed persistent infections.

Question 8

Which of the following best explains why antibiotics that target peptidoglycan are selectively toxic to bacteria?

Accepted Answer

Bacterial cell walls contain peptidoglycan, which is absent in human cells.

Question 9

Which of the following is a key difference between Gram-positive and Gram-negative bacterial cell envelopes?

Accepted Answer

Gram-negative bacteria have both an inner and outer membrane, with thin peptidoglycan in between.

Question 10

Which of the following statements about endospores is correct?

Accepted Answer

Endospores are dormant, resistant structures formed by some bacteria for survival under harsh conditions.

Question 11

Which of the following best describes the function of fimbriae in bacteria?

Accepted Answer

Fimbriae help bacteria attach to surfaces and host tissues, aiding colonization and biofilm formation.

Question 12

Which of the following is a correct pairing of a microbe and its ecological or medical significance?

Accepted Answer

Cyanobacteria – nitrogen fixation and oxygenic photosynthesis

Question 13

Which of the following statements about viruses is true?

Accepted Answer

Viruses are acellular infectious particles that require living host cells to replicate.

Question 14

Which of the following best explains why mycoplasmas are resistant to antibiotics that inhibit cell wall synthesis?

Accepted Answer

Mycoplasmas lack cell walls and instead use membrane sterols for stability.

Question 15

Which of the following is a function of the bacterial plasma membrane?

Accepted Answer

It is the site of selective permeability, energy metabolism, and nutrient transport.

Question 16

Which of the following best describes the process of group translocation in bacteria?

Accepted Answer

It modifies a molecule as it is transported into the cell, often using phosphoenolpyruvate as an energy source.

Question 17

Which of the following is a correct statement about the Gram stain?

Accepted Answer

Gram-positive cells have thick peptidoglycan that retains the crystal violet-iodine complex, staining them purple.

Question 18

Which of the following is a reason why Koch's postulates may not always be applicable in modern microbiology?

Accepted Answer

Some pathogens cannot be grown in pure culture or cause disease only in humans.

Question 19

Which of the following best explains why electron microscopy can reveal details not visible with standard light microscopy?

Accepted Answer

Electron beams have much shorter wavelengths than visible light, allowing higher resolution.

Microbes, Disease, and the Microbiome: Core Concepts and Classification

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