CHAPTER 4
An Introduction of Cell Structure and Host-Pathogen Relationships
Microbiology: A Clinical Approach, First Edition
© 2010 Garland Science Publishing
Questions
4-1:
Which of the following is the classification for a living organism that lacks a nucleus and other
membrane-bound structures?
(a)
organelle
(b)
eukaryote
(c)
spirochete
(d)
prokaryote
(e)
plasmid
4-2:
Bacteria which have a spherical or ovoid shape are called _____.
(a)
bacilli
(b)
coccobacilli
(c)
fusiform bacilli
(d)
spirilla
(e)
cocci
4-3:
_____ are spiral bacteria that are flexible and undulating.
(a)
fusiform bacilli
(b)
spirilla
(c)
streptobacilli
(d)
spirochetes
(e)
pleomorphic
4-4:
Which of the following does not include a multicellular arrangement seen with spherical
bacteria?
(a)
streptococcus
(b)
streptobacillus
(c)
tetrad
(d)
staphylococcus
(e)
diplococcus
4-5:
A patient has been diagnosed with the sexually transmitted disease gonorrhea. Which of the
following would be seen microscopically when examining the patient’s sample?
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(a)
(b)
(c)
(d)
(e)
streptococci
diplococci
coccobacilli
tetrads
staphylococci
4-6:
An outbreak of food poisoning occurs at a family picnic after the growth of Staphylococcus
aureus in unrefrigerated potato salad left sitting in the hot sun for several hours. Microscopic
examination of the potato salad reveals _____.
(a)
long chains of cocci
(b)
diplococci
(c)
tetrads
(d)
clusters of cocci
(e)
spirilla
4-7:
Which of the following is not an example of a basic dye and is repelled by capsules?
(a)
methylene blue
(b)
nigrosin
(c)
safranin
(d)
crystal violet
(e)
carbolfuchsin
4-8:
The _____ is not an example of a differential stain.
(a)
endospore stain
(b)
Gram stain
(c)
acid-fast stain
(d)
simple stain
(e)
flagella stain
4-9:
A(n) _____ is used for the purpose of viewing the shape and arrangement of bacteria and
employs a single basic dye.
(a)
simple stain
(b)
endospore stain
(c)
negative stain
(d)
acid-fast stain
(e)
differential stain
4-10:
The majority of bacteria are either _____ or _____.
(a)
Gram-positive; Gram-variable
(b)
Gram-negative; Gram-variable
(c)
Gram-positive; Gram-negative
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(d)
(e)
Gram-negative; Gram-nonreactive
Gram-variable; Gram-nonreactive
4-11:
_____ bacteria lose their crystal violet when the decolorizer alcohol is added during the Gram
stain procedure.
(a)
Gram-negative
(b)
Gram-positive
(c)
Gram-intensive
(d)
Gram-dormant
4-12:
In the Gram stain, _____ is used as a mordant to stabilize crystal violet in _____ cells.
(a)
alcohol; Gram-positive
(b)
alcohol; Gram-negative
(c)
iodine; Gram-positive
(d)
iodine; Gram-negative
(e)
safranin; Gram-nonreactive
4-13:
Which of the following explains why it is necessary to use safranin in the Gram stain?
(a)
Gram-positive bacteria do not have a strong affinity for crystal violet, but do bind well to
safranin.
(b)
Gram-negative bacteria are rendered colorless after the decolorizer is added, and need to
be counterstained to be visible under the microscope.
(c)
Safranin is the mordant needed to set the crystal violet color and make it permanent.
(d)
Gram-variable cells do not bind to crystal violet and need to be counterstained to be
visible under the microscope.
(e)
None of the above are true.
4-14:
What is the function of a flagellum?
(a)
escape from host defenses
(b)
motility
(c)
resistance to antibiotics
(d)
resistance of disinfectants
(e)
endospore formation
4-15:
Flagella are very difficult to observe microscopically because _____.
(a)
they are very thin
(b)
they resist basic dyes
(c)
they resist acidic dyes
(d)
they do not adhere to glass slides
4-16:
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Indicate whether each of the following statements is true or false. If the answer is false, explain
why.
(a)
Bacteria which have a capsule are able to resist host defense mechanisms.
(b)
To view a flagellum under a conventional microscope, it is necessary to coat it with
layers of dye or metals.
(c)
Acid-fast bacteria stain equally well with the acid-fast stain and the Gram stain.
(d)
Only bacteria containing mycolic acid in their cell wall are acid-fast.
(e)
The decolorizer in the acid-fast stain is alcohol.
4-17:
An appropriate stain for a sputum sample from a patient with tuberculosis is the _____ stain.
(a)
Gram
(b)
flagella
(c)
acid-fast
(d)
endospore
(e)
negative
4-18:
Which of the following leads to an increase in the susceptibility to infection?
(a)
malnutrition
(b)
poverty
(c)
crowded housing conditions
(d)
unsanitary conditions
(e)
all of the above
4-19:
Which of the following is a mismatched pair?
(a)
primary pathogen; disease in uncompromised host
(b)
pathogenicity islands; virulence gene clusters
(c)
environmental surveillance; quorum sensing
(d)
aggregated assemblies of bacteria; biofilm
(e)
opportunistic; mutually beneficial to host and microorganism
4-20:
Organisms that exploit a host’s decreased resistance to infection and cause disease are referred to
as _____.
(a)
auto-inducers
(b)
opportunists
(c)
primary pathogens
(d)
mutualistic pathogens
(e)
quorum sensors
4-21:
A successful infection by a pathogen requires that _____. (Select all that apply.)
(a)
the pathogen is able to multiply
(b)
the host’s immune defenses are never compromised
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(c)
(d)
(e)
the pathogen is transmissible to new hosts
a mutualistic association between host and pathogen forms
biofilms must form at the site of infection
4-22:
Clusters of genes encoding virulence factors are known as _____.
(a)
plasmids
(b)
pathogenicity islands
(c)
quorum clusters
(d)
adherence factors
(e)
inducing genes
4-23:
Mobile genetic elements that sometimes carry pathogenicity islands are known as _____.
(a)
virulence chromosomes
(b)
biofilms
(c)
plasmids
(d)
opportunistic elements
(e)
proteasomes
4-24:
All of the following are present in prokaryotic cells except ____.
(a)
peptidoglycan
(b)
cilia
(c)
capsules
(d)
pili
(e)
plasmids
4-25:
All of the following are present in eukaryotic cells except _____.
(a)
slime layer
(b)
plasmids
(c)
Golgi apparatus
(d)
cholesterol
(e)
80S ribosomes
4-26:
_____ are membrane-bound components found in eukaryotic cells.
(a)
microtubules
(b)
flagella
(c)
intermediate filaments
(d)
ribosomes
(e)
peroxisomes
4-27:
Which of the following is not associated with the eukaryotic plasma membrane?
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(a)
(b)
(c)
(d)
(e)
peptidoglycan
proteins
phospholipids
cholesterol
cytoskeletal microfilaments
4-28:
When an antibiotic targets a pathogen-specific component, it carries out _____.
(a)
receptor-mediated endocytosis
(b)
ubiquitylation
(c)
inhibition of a biochemical function that is unique to the pathogen
(d)
quorum sensing
4-29:
Which of the following describes the correct pathway used by eukaryotic cells for the synthesis
of proteins transported out of the cell?
(a)
endoplasmic reticulum \rightarrow ribosomes \rightarrow Golgi apparatus \rightarrow
plasma membrane
(b)
plasma membrane \rightarrow ribosomes \rightarrow Golgi apparatus \rightarrow
endoplasmic reticulum
(c)
Golgi apparatus \rightarrow ribosomes \rightarrow endoplasmic reticulum \rightarrow
plasma membrane
(d)
ribosomes \rightarrow endoplasmic reticulum \rightarrow Golgi apparatus \rightarrow
plasma membrane
4-30:
Endoplasmic reticulum that is not bound by ribosomes is called _____.
(a)
Golgi apparatus
(b)
smooth endoplasmic reticulum
(c)
a peroxisome
(d)
a biofilm
(e)
rough endoplasmic reticulum
4-31:
Lysosomes are produced in the _____.
(a)
endoplasmic reticulum
(b)
Golgi apparatus
(c)
nucleus
(d)
plasma membrane
(e)
proteasome
4-32:
Which of the following is a mismatched pair?
(a)
peroxisomes; fatty acid degradation
(b)
nucleus; DNA and RNA synthesis
(c)
nucleolus; ribosomal RNA synthesis
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(d)
(e)
proteasome; protein synthesis
mitochondria; ATP synthesis
4-33:
You are teaching a class the principles of the Gram stain. Discuss which controls you will use to
illustrate what happens during the decolorizing step.
4-34:
Explain why basic dyes and not acidic dyes are used when examining the morphology and
arrangement of bacterial cells.
4-35:
A.
Explain why it is of clinical value to determine whether an infection is caused by a
bacterium that possesses a capsule.
B.
Identify a stain that can be used to confirm the presence of a capsule.
4-36:
Discuss the difference between opportunistic and primary pathogens and the circumstances
under which they cause disease.
4-37:
A.
What is a biofilm?
B.
Why are biofilms clinically problematic? Provide a specific example.
4-38:
Explain why a high mortality (death) rate is not necessarily a favorable outcome for a pathogen.
4-39:
A.
Describe quorum sensing.
B.
Why is it advantageous for a pathogen to use quorum sensing during an infection?
4-40:
A.
Describe the molecular composition and structure of the phospholipid bilayer.
B.
Where is the phospholipid bilayer located in (i) prokaryotic cells and (ii) eukaryotic cells?
4-41:
Name and describe the three components that contribute to the cytoskeleton in eukaryotic cells.
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4-42:
Explain why ribosomes are suitable therapeutic targets for some, but not all, infections.
4-43:
A.
What is the endosymbiont theory?
B.
Provide an example of this process.
4-44:
Describe the three ways in which endocytosis occurs in eukaryotic cells.
4-45:
Describe two ways in which pathogens can escape the toxic effects of lysosomes once they have
been phagocytosed.
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Answers
4-1:
(d)
4-2:
(e)
4-3:
(d)
4-4:
(b)
4-5:
(b)
4-6:
(d)
4-7:
(b)
4-8:
(d)
4-9:
(a)
4-10: (c)
4-11: (a)
4-12: (c)
4-13: (b)
4-14: (b)
4-15: (a)
4-16:
Choice (c) is false: acid-fast bacteria stain ineffectively, if at all, with the Gram stain.
Choice (e) is false: the decolorizer in the acid-fast stain is acid.
4-17: (c)
4-18: (e)
4-19: (e)
4-20: (b)
4-21: (a), (c)
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4-22: (b)
4-23: (c)
4-24: (b)
4-25: (a)
4-26: (e)
4-27: (a)
4-28: (c)
4-29: (d)
4-30: (b)
4-31: (b)
4-32: (d)
4-33:
Gram-positive and Gram-negative bacteria, either mixed together on the same slide or on
separate slides, will be treated through the decolorizing step and then viewed under the
microscope. The Gram-positive sample will appear purple because the cells retain the crystal
violet after the alcohol treatment. The Gram-negative sample will appear colorless because these
cells lose the crystal violet when treated with alcohol.
4-34:
To view the structure and cell arrangement of bacteria, which are otherwise colorless, you must
use a dye that adheres to the surface of the cell, making it visible through a microscope. Basic
dyes contain positively charged molecules, whereas acidic dyes contain negatively charged
molecules. Because bacterial cells have negative charges distributed over their entire surface,
basic dyes would be attracted to the surface and bind, but acidic dyes would be repelled.
4-35:
A.
If a bacterium has a capsule it is more difficult to eradicate, for several reasons. The
capsule provides resistance to antibiotics, disinfectants, and antiseptics by blocking accessibility
to the cell. Capsules also inhibit host defenses and therefore persist for longer periods during an
infection.
B.
The negative stain is appropriate for capsule detection because an acidic dye, such as
India ink or nigrosin, is used that stains the background but is repelled by the capsule
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surrounding the bacterial cell. If desired, a second dye can be used to color the bacterial cell
inside the capsule.
4-36:
Opportunistic pathogens cause disease in hosts who have an increased susceptibility compared
with other, healthier, hosts. Elevated susceptibility may result from poverty, crowded housing,
poor diet, unsanitary living conditions, and acquired or inherited immunodeficiencies. In healthy
hosts, opportunistic pathogens usually do not pose a threat because they are unable to get past the
first line of immune defense of the host.
In contrast, primary pathogens pose a threat to healthy and susceptible individuals because the
pathogen is armed with virulence factors that overcome the host’s defenses and favor
multiplication in the host.
4-37:
A.
A biofilm forms when bacteria adhere, aggregate, and multiply on a surface.
B.
Biofilms that form in the body are often impenetrable to antibiotics and host defense
molecules. Protein films made by fibronectin, fibrinogen, albumin, and other host proteins get
deposited on artificial surfaces used clinically such as prosthetic devices. These proteins then
adhere to bacteria and a biofilm is formed over time, leading to potential complications. As
bacteria accumulate on the device, they can be absorbed into it. In addition, the biofilm is highly
resistant to host defenses. In severe cases, detachment of large pieces of the biofilm can lead to
the spread of the biofilm to secondary locations, perhaps even causing blood clots.
4-38:
If the host dies as a result of an infection, then the opportunity for transmission of the pathogen
to susceptible hosts decreases. The pathogen will survive only if transmission to new hosts is
continuous.
4-39:
A.
Quorum sensing is the mechanism used by many bacteria to regulate gene expression
based on cell density. Bacteria communicate by releasing and detecting diffusible sensing
proteins.
B.
A pathogen benefits from quorum sensing because it can delay the transcription of its
virulence genes until sufficient numbers have multiplied to the level needed to make the host ill.
In addition, postponing the expression of virulence genes is a good tactic for evading host
defenses.
4-40:
A.
The phospholipid bilayer consists of two layers of phospholipids. Each phospholipid
contains a glycerol molecule bound to a polar, phosphate-containing hydrophilic “head” and two
nonpolar, hydrophobic fatty acid “tails.” The polar groups face outward and interact with an
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aqueous environment, whereas the nonpolar groups face inward and serve to separate the
aqueous environments on opposite sides of the bilayer.
B.
(i)
Prokaryotic cells use a phospholipid bilayer for the plasma membrane.
(ii)
Eukaryotic cells use a phospholipid bilayer for the plasma membrane in addition to
membrane-bound structures inside the cell including, but not limited to, mitochondria,
endoplasmic reticulum, Golgi apparatus, and the nucleus.
4-41:
The three cytoskeletal elements include microfilaments, intermediate filaments, and
microtubules. Microfilaments are made of actin and they anchor the cytoskeleton to plasma
membrane-associated proteins. Intermediate filaments are made of keratin and they give strength
and stability to the cytoskeleton and also position neighboring cells in tissues. Microtubules are
made of tubulin and they make up cilia and flagella; they also move cell structures in the
cytoplasm, such as chromosomes during mitosis and meiosis.
4-42:
Ribosomes are appropriate targets for inactivation during bacterial but not viral infections.
Bacterial ribosomes are structurally different from the ribosomes of the infected host. Therefore
drugs designed to bind to and inactivate bacterial ribosomes would not have any deleterious side
effects in the host taking the drug because of the selective toxicity of the drug. During a viral
infection, the host’s ribosomes are exploited by the virus for protein synthesis of all protein
components needed for new viral particles. Drugs targeting the ribosomes in this instance would
inhibit host ribosomes, which would have dire consequences for the host.
4-43
A.
The endosymbiont theory proposes that during the evolution of more complex eukaryotic
organisms, a symbiosis between bacteria and eukaryotic organisms occurred allowing them to
coexist as a single unit. With time, the symbiosis became permanent and gave rise to the
formation of an organelle.
B.
An example is the mitochondrion. Bacteria share many characteristics with mitochondria
including autonomous replication, possession of a single, circular chromosome, the same type of
ribosomes (70S), similar mechanisms of ATP production, and structurally similar enzymes used
for RNA and DNA synthesis.
4-44:
(i) Pinocytosis involves the uptake of small molecules from extracellular fluid and the formation
of vesicles by the pinching in of the plasma membrane.
(ii) Phagocytosis involves the uptake of larger particles, such as pathogens, and the formation of
vesicles by the development of pseudopodia.
(iii) Receptor-mediated endocytosis involves the uptake of extracellular material by using
specific receptors on the plasma membrane, and the formation of vesicles.
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4-45
(i) Some pathogens produce substances that protect them from the degradative enzymes located
in lysosomes and can therefore survive and multiply within the phagocytic vesicle.
(ii) Some pathogens break down the lysosome and gain entry into the cytoplasm, where they
survive and multiply.
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