Microbiology The Human Experience 1st Edition By John W. Foster - Test Bank

Microbiology The Human Experience 1st Edition By John W. Foster – Test Bank

 

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Sample Questions Are Posted Below

 

Chapter 05: Cell Biology of Bacteria and Eukaryotes

 

MULTIPLE CHOICE

 

1. In this scanning electron micrograph of Borrelia burgdorferi, which of the following structures is visible?

a.	the outer sheath	c.	the genome
b.	cytoplasmic filaments	d.	flagellar motors

 

 

ANS:  A                    DIF:    Easy               REF:   5.1

OBJ:   5.1a Describe the structure and function of the bacterial cell wall, and explain its importance as a target for antibiotics.                          MSC:             Analyzing

 

2. The cell wall is part of the

a.	cell membrane.	c.	cell envelope.
b.	cytoplasm.	d.	proteome.

 

 

ANS:  C                    DIF:    Moderate       REF:   5.1

OBJ:   5.1a Describe the structure and function of the bacterial cell wall, and explain its importance as a target for antibiotics.                          MSC:             Understanding

 

3. Lipopolysaccharides are found in

a.	Gram-positive bacteria.	c.	archaea.
b.	Gram-negative bacteria.	d.	eukaryotic microbes.

 

 

ANS:  B                    DIF:    Easy               REF:   5.1

OBJ:   5.1b Explain the Gram-negative envelope structure and the role of LPS in pathogenesis.

MSC:  Remembering

 

4. In Gram-negative bacteria, peptidoglycan is found in the

a.	cytoplasm.	c.	outer membrane.
b.	inner membrane.	d.	periplasm.

 

 

ANS:  D                    DIF:    Moderate       REF:   5.1

OBJ:   5.1b Explain the Gram-negative envelope structure and the role of LPS in pathogenesis.

MSC:  Understanding

 

5. In this model of a Gram-negative bacterial cell envelope, which line is drawn to the periplasm?

a.	1	c.	3
b.	2	d.	4

 

 

ANS:  C                    DIF:    Easy               REF:   5.1

OBJ:   5.1b Explain the Gram-negative envelope structure and the role of LPS in pathogenesis.

MSC:  Applying

 

6. In this model of a Gram-negative bacterial cell envelope, which line is drawn to lipopolysaccharides?

a.	1	c.	3
b.	2	d.	4

 

 

ANS:  A                    DIF:    Easy               REF:   5.1

OBJ:   5.1b Explain the Gram-negative envelope structure and the role of LPS in pathogenesis.

MSC:  Applying

 

7. The majority of the bacterial cell cytoplasm (by total weight) is

a.	DNA.	c.	protein.
b.	RNA.	d.	water.

 

 

ANS:  D                    DIF:    Easy               REF:   5.1

OBJ:   5.1c Describe the biochemical composition of a bacterial cell.

MSC:  Remembering

 

8. In an E. coli cell, which molecule is found in only 1–2 copies per cell?

a.	DNA	c.	protein
b.	RNA	d.	phospholipids

 

 

ANS:  A                    DIF:    Moderate       REF:   5.1

OBJ:   5.1c Describe the biochemical composition of a bacterial cell.

MSC:  Remembering

 

9. Which bacterial cellular constituent is most liable to change under changing environmental conditions?

a.	DNA	c.	polyamines
b.	peptidoglycan	d.	proteins

 

 

ANS:  D                    DIF:    Difficult         REF:   5.1

OBJ:   5.1c Describe the biochemical composition of a bacterial cell.

MSC:  Applying

 

10. The cell membrane stores energy by maintaining a separation of

a.	DNA.	c.	ions.
b.	proteins.	d.	lipids.

 

 

ANS:  C                    DIF:    Moderate       REF:   5.2

OBJ:   5.2a Describe the functions of a cell membrane.                 MSC:  Understanding

 

11. In Gram-negative bacteria the cell membrane separates the

a.	periplasm from the external environment.
b.	cytoplasm from the external environment.
c.	cytoplasm from the nucleoid.
d.	DNA from the RNA.

 

 

ANS:  B                    DIF:    Moderate       REF:   5.2

OBJ:   5.2a Describe the functions of a cell membrane.                 MSC:  Understanding

 

12. In the image shown the circles and squares indicate molecules. The circles are at a higher concentration outside the cell and the squares are at a higher concentration inside the cell. Which of the following statements is correct?

a.	Energy is released if the circles move into the cell or if the squares move out of the cell.
b.	Energy is released if the circles move into the cell or if the squares move into the cell.
c.	Energy is released if the circles move out of the cell or if the squares move out of the cell.
d.	Energy is released if the circles move out of the cell or if the squares move into the cell.

 

 

ANS:  A                    DIF:    Difficult         REF:   5.2

OBJ:   5.2b Explain how nutrients are transported and how energy is spent to drive transport.

MSC:  Evaluating

 

13. In this image the energy released by the transport of the circles out of the cell is used to drive the import of the squares into the cell. This is an example of

a.	passive transport.	c.	symport coupled transport.
b.	facilitated diffusion.	d.	antiport coupled transport.

 

 

ANS:  D                    DIF:    Moderate       REF:   5.2

OBJ:   5.2b Explain how nutrients are transported and how energy is spent to drive transport.

MSC:  Understanding

 

14. In this image a transmembrane protein moves circles out of the cell, providing energy to move squares into the cell. Which of the following is correct?

a.	Both the circles and the squares move down their concentration gradients.
b.	Both the circles and the squares move against their concentration gradients.
c.	The circles move down their concentration gradient and the squares move against their concentration gradient.
d.	The circles move against their concentration gradient and the squares move down their concentration gradient.

 

 

ANS:  C                    DIF:    Moderate       REF:   5.2

OBJ:   5.2b Explain how nutrients are transported and how energy is spent to drive transport.

MSC:  Understanding

 

15. What is the cellular target of penicillin (the first antibiotic discovered)?

a.	the DNA genome	c.	ribosomes
b.	the cell wall	d.	ABC transporters

 

 

ANS:  B                    DIF:    Easy               REF:   5.1

OBJ:   5.1a Describe the structure and function of the bacterial cell wall, and explain its importance as a target for antibiotics.                          MSC:             Remembering

 

16. How does the cell wall protect bacterial cells from osmotic shock?

a.	The wall forms a rigid cage that withstands turgor pressure.
b.	The wall is impermeable to water, preventing turgor pressure.
c.	The wall is impermeable to ions and other solutes, preventing osmotic imbalance.
d.	The wall ensures cells are only found in environments where turgor pressure will not occur.

 

 

ANS:  A                    DIF:    Moderate       REF:   5.3

OBJ:   5.3a Describe the cell wall structure, and explain how it protects bacteria from osmotic shock.

MSC:  Understanding

 

17. The bacterial cell wall is an attractive target for antibiotics because

a.	bacterial cells cannot develop resistance to antibiotics that target the cell wall.
b.	animal cells lack a cell wall.
c.	the cell wall is unimportant for bacterial survival.
d.	the cell wall is the only structure bacteria require for survival.

 

 

ANS:  B                    DIF:    Moderate       REF:   5.1

OBJ:   5.1a Describe the structure and function of the bacterial cell wall, and explain its importance as a target for antibiotics.                          MSC:             Applying

 

18. Mycoplasma lost their cell walls via reductive evolution. This was possible because

a.	their cell membranes became extra thick to compensate.
b.	it allowed them to not be sensitive to antibiotics that target the cell wall.
c.	as obligate parasites they live in environments with constant osmolarity.
d.	they live in soils with plenty of available moisture.

 

 

ANS:  C                    DIF:    Difficult         REF:   5.3

OBJ:   5.3a Describe the cell wall structure, and explain how it protects bacteria from osmotic shock.

MSC:  Analyzing

 

19. This image models a

a.	Gram-positive cell envelope.	c.	eukaryotic cell membrane.
b.	Gram-negative cell envelope.	d.	mycobacterial envelope.

 

 

ANS:  A                    DIF:    Easy               REF:   5.3

OBJ:   5.3b Explain the function of the Gram-positive cell wall and teichoic acids.

MSC:  Remembering

 

20. Which of the following is FALSE of teichoic acids?

a.	They reinforce the cell wall.
b.	They may help pathogens attach to host cells.
c.	They are recognized by the host immune system.
d.	They repel the Gram stain.

 

 

ANS:  D                    DIF:    Moderate       REF:   5.3

OBJ:   5.3b Explain the function of the Gram-positive cell wall and teichoic acids.

MSC:  Analyzing

 

21. This transmission electron micrograph shows a

a.	Gram-positive cell envelope.	c.	eukaryotic cell membrane.
b.	Gram-negative cell envelope.	d.	mycobacterial envelope.

 

 

ANS:  B                    DIF:    Moderate       REF:   5.3

OBJ:   5.3c Explain the function of the Gram-negative outer membrane, LPS, and periplasm.

MSC:  Applying

 

22. Murein lipoprotein is a part of the ________ of the ________.

a.	outer leaflet, outer membrane.	c.	outer leaflet, inner membrane.
b.	inner leaflet, outer membrane.	d.	inner leaflet, inner membrane.

 

 

ANS:  B                    DIF:    Moderate       REF:   5.3

OBJ:   5.3c Explain the function of the Gram-negative outer membrane, LPS, and periplasm.

MSC:  Remembering

 

23. Which of the following is a function of lipopolysaccharide?

a.	helps cells resist phagocytosis
b.	aids in outer membrane cell wall attachment
c.	allows for mobility to promote chemotaxis
d.	provides energy to the cell

 

 

ANS:  A                    DIF:    Moderate       REF:   5.3

OBJ:   5.3c Explain the function of the Gram-negative outer membrane, LPS, and periplasm.

MSC:  Understanding

 

24. Which of the following helps compact bacterial DNA?

a.	the origin of replication site	c.	porins
b.	supercoils	d.	pilins

 

 

ANS:  B                    DIF:    Easy               REF:   5.4

OBJ:   5.4a Describe how DNA is organized within the bacterial cell.

MSC:  Remembering

 

25. Which of the following is true of growing bacteria?

a.	DNA synthesis occurs continuously.
b.	DNA synthesis occurs during a defined period.
c.	They suspend flagella rotation to put energy toward DNA replication.
d.	DNA synthesis cannot occur at the same time as transcription.

 

 

ANS:  A                    DIF:    Easy               REF:   5.4

OBJ:   5.4b Explain how DNA replication is coordinated with cell growth and division.

MSC:  Remembering

 

26. The arrows indicate the partition that separates a bacterial cell into two new daughter cells. This partition is called the

a.	stalk.	c.	septum.
b.	S-layer.	d.	termination site.

 

 

ANS:  C                    DIF:    Easy               REF:   5.4

OBJ:   5.4b Explain how DNA replication is coordinated with cell growth and division.

MSC:  Remembering

 

27. Bacterial cells that expand their cell walls during septation (not before) and septate in parallel planes will form

a.	chains of rods (bacilli).	c.	chains of spheres (cocci).
b.	tetrads of rods (bacilli).	d.	tetrads of spheres (cocci).

 

 

ANS:  C                    DIF:    Difficult         REF:   5.4

OBJ:   5.4b Explain how DNA replication is coordinated with cell growth and division.

MSC:  Evaluating

 

28. This electron micrograph shows staphylococci, spherical cells that cluster together like grape bunches. This form occurs when cell wall expansion occurs

a.	prior to septation and septation occurs  in parallel planes.
b.	prior to septation and septation occurs in random orientations.
c.	during septation and septation occurs  in parallel planes.
d.	during septation and septation occurs in random orientations.

 

 

ANS:  D                    DIF:    Moderate       REF:   5.4

OBJ:   5.4b Explain how DNA replication is coordinated with cell growth and division.

MSC:  Applying

 

29. Which of the following structures is obligatory for all bacterial cells?

a.	nucleoid	c.	pili
b.	flagella	d.	magnetosomes

 

 

ANS:  A                    DIF:    Easy               REF:   5.5

OBJ:   5.5a Describe how pili and stalks enable bacteria to adhere to a substrate where conditions are favorable.   MSC:           Understanding

 

30. Pili and stalks enable bacterial

a.	adherence.	c.	photosynthesis.
b.	chemotaxis.	d.	symport.

 

 

ANS:  A                    DIF:    Easy               REF:   5.5

OBJ:   5.5a Describe how pili and stalks enable bacteria to adhere to a substrate where conditions are favorable.   MSC:           Remembering

 

31. While most wild E. coli usually have flagella, many lab strains have lost their flagella. What is a likely cause of this loss?

a.	reductive evolution due to an increased need for chemotaxis
b.	reductive evolution due to an unchanging environment
c.	reductive evolution due to an increased need for magnetotaxis
d.	reductive evolution due to a decreased need for magnetotaxis

 

 

ANS:  B                    DIF:    Difficult         REF:   5.5

OBJ:   5.5b Explain how flagellar motility and chemotaxis enable bacteria to respond to environmental change.    MSC:           Analyzing

 

32. Flagella are required for bacterial

a.	chemotaxis.	c.	adherence.
b.	growth.	d.	buoyancy.

 

 

ANS:  A                    DIF:    Moderate       REF:   5.5

OBJ:   5.5b Explain how flagellar motility and chemotaxis enable bacteria to respond to environmental change.    MSC:           Understanding

 

33. This transmission electron micrograph of a marine microbe shows internal structures such as thylakoids. This microbe has what capability that is not present in all bacterial species?

a.	adherence	c.	DNA replication
b.	chemotaxis	d.	photosynthesis

 

 

ANS:  D                    DIF:    Moderate       REF:   5.5

OBJ:   5.5c Describe the functions of thylakoids, storage granules, and magnetosomes.

MSC:  Applying

 

34. Magnetotactic bacteria swim along a magnetic field. To do this these bacteria have which of the following structures that are not present in all bacterial species?

a.	storage granules	c.	flagella
b.	sulfur granules	d.	gas vesicles

 

 

ANS:  C                    DIF:    Difficult         REF:   5.5

OBJ:   5.5c Describe the functions of thylakoids, storage granules, and magnetosomes.

MSC:  Applying

 

35. Which organelle is NOT part of the endomembrane system?

a.	mitochondrion	c.	peroxisome
b.	lysosome	d.	Golgi complex

 

 

ANS:  A                    DIF:    Easy               REF:   5.6

OBJ:   5.6a Explain the structure and interconnection of membranous organelles in the endomembrane system.     MSC:           Remembering

 

36. Ribosomes associate with which endomembrane organelle?

a.	Golgi complex	c.	lysosomes
b.	endoplasmic reticulum	d.	peroxisomes

 

 

ANS:  B                    DIF:    Easy               REF:   5.6

OBJ:   5.6a Explain the structure and interconnection of membranous organelles in the endomembrane system.     MSC:           Remembering

 

37. Which of the following shows the correct path a secreted protein takes in a eukaryotic cell?

a.	Golgi complex, rough ER, vesicle, cell membrane
b.	vesicle, rough ER, Golgi complex, cell membrane
c.	rough ER, Golgi complex, vesicle, cell membrane
d.	rough ER, Golgi complex, cell membrane, vesicle

 

 

ANS:  C                    DIF:    Moderate       REF:   5.6

OBJ:   5.6b Describe the functions of the Golgi complex, endoplasmic reticulum, and nuclear membrane. MSC:           Understanding

 

38. Which organelle houses a eukaryotic cell’s genome?

a.	rough endoplasmic reticulum	c.	ribosome
b.	contractile vacuole	d.	nucleus

 

 

ANS:  D                    DIF:    Easy               REF:   5.6

OBJ:   5.6b Describe the functions of the Golgi complex, endoplasmic reticulum, and nuclear membrane. MSC:           Remembering

 

39. Which organelle arose via endosymbiosis?

a.	chloroplast	c.	lysosome
b.	Golgi apparatus	d.	nucleus

 

 

ANS:  A                    DIF:    Easy               REF:   5.6

OBJ:   5.6c Explain how the evolutionary process of endosymbiosis led to mitochondria and chloroplasts. MSC:           Remembering

 

40. ATP synthase is found in bacterial cell membranes. In eukaryotic cells, ATP synthase is found in the

a.	cell membrane.	c.	mitochondrial inner membrane.
b.	cytoplasm.	d.	mitochondrial matrix.

 

 

ANS:  C                    DIF:    Moderate       REF:   5.6

OBJ:   5.6c Explain how the evolutionary process of endosymbiosis led to mitochondria and chloroplasts. MSC:           Applying

 

41. CASE HISTORY

In the Indian state of Bihar, a school nurse noticed that a 13-year-old boy, Naranjan, had swelling on his nose and lips. When questioned, Naranjan complained of a pruritic (itchy) rash on his arms and legs. Upon examination, the nurse found pale patches of skin on his back. The pale patches lacked sensation, and there was partial loss of sensation in Naranjan’s wrists and forearms. The patient was diagnosed with leprosy, caused by the bacterium Mycobacterium leprae. The bacteria stain acid-fast and are spread primarily by nasal secretions. For unknown reasons, only 5% of people exposed to the bacteria are susceptible to infection. In a susceptible host, the bacteria can grow slowly for many years without symptoms. They infect the peripheral nerves, causing loss of sensation, and the body’s immune reaction generates skin lesions. To halt the disease, Naranjan was started on a two-year course of multidrug therapy combining dapsone, clofazimine, and rifampin. To monitor hepatotoxicity, liver function tests were ordered. Naranjan’s family and neighbors were screened; one member, an uncle, showed skin lesions. The uncle was treated also. Leprosy is difficult to eradicate because of the long incubation period and because people hide their symptoms, fearing stigma as “lepers.”

 

Mycobacterium leprae, or leprosy disease, often takes years to develop. Naranjan must use a long-term multidrug therapy to cure it. Why is it necessary to take the drugs for such a long period, and why must he take so many drugs at once?

a.	Mycobacteria are Gram-negative organisms. They must be killed slowly to prevent release of toxic LPS.
b.	Mycolic acid within the cell wall reduces nutrient uptake, resulting in slow growth, and excludes some antibiotics.
c.	Mycobacteria are all highly resistant to antibiotics.
d.	Mycobacteria don’t have cell walls, so must be treated with antibiotics that target other structures.

 

 

ANS:  B                    DIF:    Moderate       REF:   Case History 5.1

OBJ:   5.1a Describe the structure and function of the bacterial cell wall, and explain its importance as a target for antibiotics. | 5.1c Describe the biochemical composition of a bacterial cell.

MSC:  Applying

 

COMPLETION

 

1. The region within the inner and outer membranes of Gram-negative bacteria is known as the ________.

 

ANS:  periplasm

 

DIF:    Moderate        REF:   5.1

OBJ:   5.1b Explain the Gram-negative envelope structure and the role of LPS in pathogenesis.

MSC:  Remembering

 

2. The bacterial nucleoid contains loops of DNA that emanate from a central point called the ________.

 

ANS:  origin of replication

 

DIF:    Moderate        REF:   5.4

OBJ:   5.4a Describe how DNA is organized within the bacterial cell.

MSC:  Remembering

 

3. The ability of bacterial cells to swim toward favorable environments and away from harmful environments is known as ________.

 

ANS:  chemotaxis

 

DIF:    Moderate        REF:   5.5

OBJ:   5.5b Explain how flagellar motility and chemotaxis enable bacteria to respond to environmental change.    MSC:           Remembering

 

4. If Na⁺ is at a higher concentration outside a cell than inside, ________ is the most likely means for sodium ions to enter the cell (and for nothing else to enter or leave).

 

ANS:  facilitated diffusion

 

DIF:    Difficult         REF:   5.2

OBJ:   5.2b Explain how nutrients are transported and how energy is spent to drive transport.

MSC:  Applying

 

5. In the process of ________, a vesicle fuses with the cell membrane, releasing vesicle contents into the extracellular environment.

 

ANS:  exocytosis

 

DIF:    Easy               REF:   5.6

OBJ:   5.6a Explain the structure and interconnection of membranous organelles in the endomembrane system.     MSC:           Remembering

 

SHORT ANSWER

 

1. Describe the two types of energy cells used to move molecules across membranes against their concentration gradients.

 

ANS:

Active transport can be powered by two different energy sources. Some transporters are directly powered by ATP hydrolysis. Other transporters use coupled transport—the movement of one molecule down its concentration gradient to provide the energy to move a second molecule against its concentration gradient.

 

DIF:    Moderate        REF:   5.2

OBJ:   5.2b Explain how nutrients are transported and how energy is spent to drive transport.

MSC:  Understanding

 

2. Compare and contrast the Gram-negative and Gram-positive cell envelopes.

 

ANS:

Both Gram-negative and Gram-positive bacteria contain a cell membrane (called the inner membrane in Gram-negative bacteria) and a peptidoglycan cell wall. Gram-negative bacteria have a thin cell wall and an additional outer membrane. Gram-positive bacteria lack an outer membrane but have a thick cell wall.

 

DIF:    Difficult         REF:   5.3

OBJ:   5.3a Describe the cell wall structure, and explain how it protects bacteria from osmotic shock.

MSC:  Analyzing

 

3. What evidence would suggest that a newly discovered eukaryotic organelle was formed via endosymbiosis?

 

ANS:

The evidence for mitochondria and chloroplasts being derived via endosymbiosis is the presence of a double membrane (the inner one from the engulfed cell, the outer one from the host eukaryote), the presence of ribosomes, and the presence of DNA. Look for these same traits in the new organelle, as all cells contain a cell membrane, genome, and ribosomes.

 

DIF:    Difficult         REF:   5.6

OBJ:   5.6c Explain how the evolutionary process of endosymbiosis led to mitochondria and chloroplasts. MSC:           Applying

 

4. Explain how bacterial cells can divide so rapidly, some in as little as ten minutes between generations.

 

ANS:

First, prokaryotic genomes are compact, with relatively little noncoding DNA. Second, the DNA replicates continuously, not just during a defined period, as in eukaryotic cells.

 

DIF:    Difficult         REF:   5.4

OBJ:   5.4b Explain how DNA replication is coordinated with cell growth and division.

MSC:  Applying

 

5. Would pili be more advantageous to bacteria in a rapidly changing or in an unchanging environment? Please explain your answer.

 

ANS:

Pili promote bacterial adherence to a substrate. This is an advantage in an unchanging environment that is rich in nutrients. In a rapidly changing environment, being stuck in one place becomes a disadvantage.

 

DIF:    Easy               REF:   5.5

OBJ:   5.5a Describe how pili and stalks enable bacteria to adhere to a substrate where conditions are favorable.   MSC:           Applying

 

6. CASE HISTORY

Sharon, the CEO of a start-up company, lives in Westchester County, a wooded community north of New York City. She spends her summer weekends e-mailing her managers from the outdoor deck of her home, shaded by tall oak trees. The acorns attract mice and deer, and the leaf litter is full of ticks (Ixodes scapularis).

One evening Sharon’s husband noticed a red rash on her back, consisting of a ring shape several centimeters across, surrounding another red spot in the middle. Sharon recalled seeing this “bull’s-eye” type of rash on the Internet. The rash was described as the hallmark of Lyme disease, or borreliosis, caused in the United States by the tick-borne bacterium Borrelia burgdorferi (in Europe, by the closely related species Borrelia afzelii). The distinctive rash, erythema migrans (“migrating redness”), begins at the site of a tick bite and expands concentrically as the bacteria migrate outward. Sharon recalled that a neighbor’s child had suffered crippling arthritis caused by an undetected case of Lyme disease. Another neighbor who contracted Lyme disease had suffered from meningitis (inflammation of the brain lining) and neurological abnormalities, including facial paralysis, ultimately losing his job and his million-dollar home.

The next day Sharon went to her doctor and was treated with the antibiotic doxycycline, a tetracycline derivative that targets the bacterial ribosome. Doxycycline is the antibiotic of choice for B. burgdorferi. Sharon was fortunate to make a full recovery before serious symptoms appeared.

 

The bull’s-eye rash that is a hallmark of Sharon’s infection is associated with movement of the bacteria from the initial site of tick bite and infection. Discuss how these bacteria move and the cell structures associated with movement.

 

ANS:

The flagellum is a helical protein filament whose rotary motor propels the cell in search of a more favorable environment, including more nutrient-right environments via chemotaxis. For spirochete bacteria such as B. burgdorferi (the cause of Lyme disease) or Treponema pallidum (the cause of syphilis), the flagella wrap around the cell body, enclosed by the outer sheath.

 

DIF:    Moderate        REF:   Chapter 5 Introduction

OBJ:   5.5b Explain how flagellar motility and chemotaxis enable bacteria to respond to environmental change.    MSC:           Applying

 

7. CASE HISTORY

Jennifer, age 23, had just graduated from college with a Fulbright fellowship to study sociology in Africa. Before leaving the United States, she obtained a routine physical exam at a large city hospital. Upon returning home from the hospital, she developed a swelling in her leg. When she returned to the hospital, she was told that the swelling represented an allergic reaction and was given anti-inflammatory agents. The swelling grew, and within a day the skin ruptured with a bloody discharge. Upon return to the emergency room, Jennifer at last received the correct diagnosis of methicillin-resistant staphylococcus infection (MRSA). A nurse commented that hospital visitors can acquire MRSA; the infectious agent is endemic at many hospitals in the United States and is very difficult to eradicate. She showed Jennifer a micrograph of the bacteria, Staphylococcus aureus, which septate in alternating division planes, thus forming clusters of cells. Jennifer required many weeks of treatment with the antibiotics doxycycline and clindamycin (inhibits protein synthesis) before the infection resolved, and she had to postpone her fellowship for a year.

 

Methicillin, the antibiotic to which MRSA is characteristically resistant, targets the cell wall. Discuss the structure of the cell wall in a bacterial cell like those of MRSA and how antibiotics can target this structure without harming the patient.

 

ANS:

Outside the cell membrane, Gram-positive bacteria have a thick cell wall with multiple layers of peptidoglycan, threaded by teichoic acids. Peptidoglycan is synonymous with murein (“wall molecule”) and consists of parallel polymers of disaccharides called glycan chains. Peptidoglycan, or murein, is unique to bacteria, never found in human cells. For this reason, antibiotics that target peptidoglycan synthesis may have minimal side effects for a patient.

 

DIF:    Moderate        REF:   Case History 5.2

OBJ:   5.1a Describe the structure and function of the bacterial cell wall, and explain its importance as a target for antibiotics.                          MSC:             Applying