CHAPTER 14 Test Your Knowledge

Driving Question 1

By answering the questions below and studying Infographic 14.1, you should be able to generate an answer for the broader Driving Question above.

KNOW IT

Can S. aureus be present in or on a person who has no evidence of an infection?
a. no; S. aureus is associated only with infections

b. yes, but only non-MRSA strains are present in the absence of an infection

c. yes, but only for very short periods of time (between touching a contaminated surface and washing your hands)

d. yes; S. aureus is a common skin bacterium

e. yes; S. aureus is a common bacterium found in the bloodstream

The term “MRSA” as it is used today refers to
a. S. aureus bacteria that are resistant to many antibiotics.

b. a collection of skin and other infections caused by a type of bacteria.

c. S. aureus bacteria that are found only in humans with certain types of skin infections.

d. S. aureus bacteria that are normal residents of human skin in the vast majority of the human population.

e. all bacteria that are resistant to antibiotics.

What is the difference between an S. aureus colonization and an S. aureus infection?

MRSA is most likely to be problematic if found
a. on the surface of the skin.

b. in nasal passages.

c. in the bloodstream.

d. on the fingernails.

e. The presence of MRSA in any of those locations indicates a serious infection.

USE IT

A young athlete has a nasty skin infection caused by MRSA. How might this infection have been contracted?

For the patient in Question 5, which general kinds of antibiotics would you choose (or avoid) in treating the infection? What other measures would you recommend to prevent spread of MRSA to the athlete’s teammates and family? Explain your answer.

Driving Question 2

By answering the questions below and studying Infographics 14.2, 14.3, and 14.4, you should be able to generate an answer for the broader Driving Question above.

KNOW IT

In the presence of penicillin:
a. What happens to a sensitive strain of S. aureus?

b. What happens to a resistant strain of S. aureus?

How do beta-lactam antibiotics kill sensitive bacteria?
a. by attracting water into cells

b. by destabilizing the cell membrane

c. by preventing DNA replication during bacterial reproduction

d. by destabilizing the cell wall

e. all of the above, depending on the specific strain of bacteria

USE IT

Why do the beta-lactam antibiotics affect sensitive bacterial cells but not eukaryotic cells? (You may want to review cell structure, discussed in Chapter 3, to answer this question.)

A sensitive S. aureus bacterium acquires a new gene that allows it to resist the effects of beta-lactam antibiotics (that is, the bacterium is now resistant). What might the protein encoded by that gene do?
a. synthesize beta-lactam antibiotics

b. digest beta-lactam antibiotics

c. produce a toxin

d. enhance colonization of human skin

e. enhance entry into the bloodstream

Driving Question 3

By answering the questions below and studying Infographics 14.5, 14.6, and 14.7, you should be able to generate an answer for the broader Driving Question above.

KNOW IT

What are the two major mechanisms by which bacterial populations generate genetic diversity?
a. mutation and meiosis

b. binary fission and evolution by natural selection

c. gene transfer and mutation

d. mutation and binary fission

e. gene transfer and replication

What is the environmental pressure in the case of antibiotic resistance?
a. the growth rate of the bacteria

b. how strong or weak the bacterial cell walls are

c. the relative fitness of different bacteria

d. the presence or absence of antibiotics in the environment

e. the temperature of the environment

What is the evolutionary meaning of the term “fitness”?

The evolution of antibiotic resistance is an example of
a. directional selection.

b. diversifying selection.

c. stabilizing selection.

d. random selection.

e. steady selection.

In humans, very-large-birth-weight babies and very tiny babies do not survive as well as midrange babies. What kind of selection is acting on human birth weight?
a. directional selection

b. diversifying selection

c. stabilizing selection

d. random selection

e. steady selection

USE IT

Binary fission is asexual. What does this mean? How could two daughter cells end up with different genomes at the end of one round of binary fission?

In what sense do bacteria “evolve faster” than other species?

If we take the most fit bacterium from one environment—one in which the antibiotic amoxicillin is abundant, for example—and place it in an environment in which a different antibiotic is abundant, will it retain its high degree of fitness?
a. yes; fitness is fitness, regardless of the environment

b. yes; once a bacterium is resistant to one antibiotic it is resistant to all antibiotics

c. not necessarily; fitness depends on the ability of an organism to survive and reproduce, and it may not do this as well in a different environment

d. no; what is fit in one environment will never be fit in another environment

If a single bacterial cell that is sensitive to an antibiotic—for example, vancomycin—is placed in a growth medium that contains vancomycin, it will die. Now consider another single bacterial cell, also sensitive to vancomycin, that is allowed to divide for many generations to become a larger population. If this population is placed into vancomycin-containing growth medium, some bacteria will grow. Why do you see growth in this case, but not with the transferred single cell?

Imagine that a genetically diverse population of garden snails occupies your backyard, in which the vegetation is many shades of green with some brown patches of dry grass.
a. If birds like to eat snails, but they can see only the snails that stand out from their background and don’t blend in, what do you think the population of snails in your backyard will look like after a period of time? Explain your answer.

b. Suppose you move the population of snails to a new environment, one with patches of dark brown pebbles and patches of yellow ground cover. Will individual snails mutate to change their color immediately? As the population evolves and adapts to the new environment, what do you predict will happen to the phenotypes in your population of snails after several generations in this new environment? How did this occur? Include the terms gametes, mutation, fitness, phenotype, and environmental selective pressure in your answer.