Deck 15: Microbial Mechanisms of Pathogenicity

Question 1

All of the following are methods of avoiding host antibodies EXCEPT

A) membrane-disrupting toxins.
B) antigenic changes.
C) inducing endocytosis.
D) IgA proteases.
E) invasins.

Answer 1

A

Question 2

The ability of some microbes, such as Trypanosoma or Giardia to alter their surface molecules and evade destruction by the hostʹs antibodies is called

A) cytocidal effect.
B) antigenic variation.
C) virulence.
D) lysogenic conversion.
E) cytopathic effect.

Answer 2

B

Question 3

Which of the following is NOT a membrane-disrupting toxin?

A) streptolysin S
B) streptolysin O
C) leukocidin
D) A-B toxin
E) hemolysin

Answer 3

D

Question 4

Botulism is caused by ingestion of a proteinaceous exotoxin; therefore, it can easily be prevented by

A) filtering food.
B) preventing fecal contamination of food.
C) boiling food prior to consumption.
D) not eating canned food.
E) administering antibiotics to patients.

Question 5

Endotoxins are

A) A-B toxins.
B) associated with gram-positive bacteria.
C) part of the gram-negative cell wall.
D) excreted from the cell.
E) molecules that bind nerve cells.

Question 6

Which of the following statements about exotoxins is generally FALSE?

A) They are composed of proteins.
B) They are more potent than endotoxins.
C) They have specific methods of action.
D) They are resistant to heat.
E) They are produced by gram-positive bacteria.

Question 7

Cytopathic effects are changes in host cells due to

A) viral infections.
B) helminthic infections.
C) protozoan infections.
D) fungal infections.
E) bacterial infections.

Question 8

The fimbriae of Neisseria gonorrhea and enteropathogenic E. coli are examples of

A) adhesins.
B) ligands.
C) receptors.
D) adhesins and ligands.
E) adhesins, ligands, and receptors.

Question 9

Siderophores are bacterial proteins that compete with the hostʹs

A) red blood cells.
B) white blood cells.
C) iron-transport proteins.
D) antibodies.
E) receptors.

Question 10

All of the following contribute to a pathogenʹs invasiveness EXCEPT

A) capsules.
B) toxins.
C) hyaluronidase.
D) coagulases.
E) cell wall components.

Question 11

All of the following organisms produce exotoxins EXCEPT

A) Salmonella typhi.
B) Clostridium tetani.
C) Staphylococcus aureus.
D) Clostridium botulinum.
E) Corynebacterium diphtheriae.

Question 12

Superantigens produce intense immune responses by stimulating lymphocytes to produce

A) leukocidins.
B) cytokines.
C) endotoxins.
D) interferons.
E) exotoxins.

Question 13

Which of the following cytopathic effects is cytocidal?

A) inclusion bodies
B) giant cells
C) transformation
D) release of enzymes from lysosomes
E) antigenic changes

Question 14

The ID50 is

A) the dose that will cause an infection in some of the test population.
B) the dose that will cause an infection in 50 percent of the test population.
C) the dose that will kill some of the test population.
D) a measure of pathogenicity.
E) the dose that will kill 50 percent of the test population.

Question 15

All of the following are examples of entry via the parenteral route EXCEPT

A) injection.
B) surgery.
C) hair follicle.
D) bite.
E) skin cut.

Question 16

Most pathogens that gain access through the skin

A) must be injected.
B) must adhere first while their invasive factors allow them to penetrate.
C) enter through hair follicles and sweat ducts.
D) can penetrate intact skin.
E) just infect the skin itself.

Question 17

Which of the following statements is FALSE?

A) Leukocidins destroy neutrophils.
B) Coagulase destroys blood clots.
C) Hyaluronidase breaks down substances between cells.
D) Hemolysins lyse red blood cells.
E) Kinase destroys fibrin clots.

Question 18

Which of the following does NOT contribute to the symptoms of a fungal disease?

A) capsules
B) metabolic products
C) cell walls
D) allergic response of the host
E) toxins

Question 19

The most frequently used portal of entry for pathogens is the

A) skin.
B) mucous membranes of the gastrointestinal tract.
C) parenteral route.
D) mucous membranes of the respiratory tract.
E) All of these portals are used equally.

Question 20

All of the following are used by bacteria to attach to host cells EXCEPT

A) A-B toxins.
B) M protein.
C) ligands.
D) capsules.
E) fimbriae.

Question 21

Cholera toxin polypeptide A binds to surface gangliosides on target cells. If the gangliosides were removed,

A) polypeptide A would enter the cells.
B) Vibrio would bind to target cells.
C) Vibrio would not produce cholera toxin.
D) polypeptide A would bind to target cells.
E) polypeptide B would not be able to enter the cells.

Question 22

Which of the following contributes to the virulence of a pathogen?

A) numbers of microorganisms that gain access to a host and evasion of host defenses
B) evasion of host defenses
C) toxin production
D) numbers of microorganisms that gain access to a host
E) numbers of microorganisms that gain access to a host, evasion of host defenses, and toxin production

Question 23

Which of the following is NOT a cytopathic effect of viruses?

A) host cells fusing to form multinucleated syncytia
B) inclusion bodies forming in the cytoplasm or nucleus
C) toxin production
D) increased cell growth
E) cell death

Question 24

Which of the following statements about M protein is FALSE?

A) It is found on Streptococcus pyogenes.
B) It is heat- and acid-resistant.
C) It is a protein.
D) It is found on fimbriae.
E) It is readily digested by phagocytes.

Question 25

Gram-negative septic shock results from the following events. What is the second step?

A) Phagocytes ingest gram-negative bacteria.
B) LPS is released from gram-negative bacteria.
C) Body temperature is reset in the hypothalamus.
D) IL-1 is released.
E) Fever occurs.

Question 26

Symptoms of intense inflammation and shock occur in some gram -positive bacterial infections due to

A) lipid A.
B) superantigens.
C) A-B toxins.
D) membrane-disrupting toxins.
E) erythrogenic toxin.

Question 27

All of the following bacteria release endotoxin EXCEPT

A) Proteus vulgaris.
B) Clostridium botulinum.
C) Salmonella typhi.
D) Neisseria meningitidis.
E) Haemophilus influenzae.

Question 28

Antibiotics can lead to septic shock if used to treat

A) viral infections.
B) gram-negative bacterial infections.
C) gram-positive bacterial infections.
D) helminth infestations.
E) protozoan infections.

Question 29

Twenty-five people developed symptoms of nausea, vomiting, and diarrhea three to six hours after attending a church picnic where they ate a ham and green bean casserole with cream sauce. The most likely cause of this case of food intoxication is

A) erythrogenic toxin.
B) aflatoxin.
C) cholera toxin.
D) staphylococcal enterotoxin.
E) botulinum toxin.

Question 30

Polio is transmitted by ingestion of water contaminated with feces containing polio virus. What portal of entry does polio virus use?

A) skin only
B) parenteral only
C) mucous membranes only
D) skin and parenteral
E) skin, parenteral, and mucous membranes

Question 31

Injectable drugs are tested for endotoxins by

A) culturing bacteria.
B) the Limulus amoebocyte lysate test.
C) filtering out the cells.
D) looking for turbidity.
E) counting the viable bacteria.

Question 32

Symptoms of protozoan and helminthic diseases are due to

A) tissue damage due to growth of the parasite on the tissues, waste products excreted by the parasite, and products released from damaged tissues.
B) products released from damaged tissues.
C) tissue damage due to growth of the parasite on the tissues.
D) tissue damage due to growth of the parasite on the tissues and waste products excreted by the parasite.
E) waste products excreted by the parasite.

Question 33

Which of the following is an example of direct damage due to bacterial infection?

A) the invasion and lysis of intestinal cells by E. coli
B) the excessive secretion of fluids in a Vibrio cholera infection
C) the fever, nausea, and low blood pressure in a Salmonella infection
D) the hemolysis of red blood cells in a staphylococcal infection
E) the uncontrolled muscle contractions in Clostridium tetani infection

Question 34

Which of the following statements about staphylococcal enterotoxin is FALSE?

A) It is a superantigen.
B) It is produced by Staphylococcus aureus growing in the hostʹs intestines.
C) It causes vomiting.
D) It causes diarrhea.
E) It is an exotoxin.

Question 35

Which of the following mechanisms is used by gram -negative bacteria to cross the blood-brain barrier?

A) producing toxins
B) inducing endocytosis
C) producing fimbriae
D) antigenic variation
E) inducing TNF

Question 36

Bacteria such as E. coli and Salmonella produce invasins that bind host cells, thus causing the cells to

A) destroy the bacteria.
B) release TNF.
C) engulf the bacteria.
D) produce iron-binding proteins.
E) release cytokines.

Question 37

Table 15.1 $\begin{array}{|l|l|l|}\hline \text { Bacterium } & \text { Portal of Entry } & \text { ID 50 } \\\hline \text { Stophylococcus aureus } & \text { Wound } & <10 \\\hline \text { Stwohylococcus aureus } & \text { Wound + Ampicillin } & 300 \\\hline\end{array}$ Table 15.1 shows the ID50 for Staphylococcus aureus in wounds with and without the administration of ampicillin before surgery. Based on the data, the administration of ampicillin before surgery

A) has no effect on risk of infection.
B) replaces tetracycline.
C) decreases the risk of staphylococcal infection.
D) increases the risk of staphylococcal infection.
E) The answer cannot be determined based on the information provided.

Question 38

Endotoxins in sterile injectable drugs could cause

A) nerve damage.
B) giant cell formation.
C) no damage, because they are sterile.
D) infection.
E) septic shock symptoms.

Question 39

Table 15.2 $\begin{array}{|l|c|}\hline \text { Bacterium } & \text { ID50 } \\\hline \text { E. coli } 0157: \mathrm{H7} & 20 \\\hline \text { Legionella pneumophia } & 1 \\\hline \text { Shigella } & 10 \\\hline \text { Treponema pallidum } & 57 \\\hline\end{array}$

-Which organism in Table 15.2 most easily causes an infection?

A) Shigella
B) Legionella pneumophila
C) Treponema pallidum
D) E. coli O157:H7
E) The answer cannot be determined based on the information provided.

Question 40

Lysogenic bacteriophages contribute to bacterial virulence because bacteriophages

A) produce toxins.
B) give new gene sequences to the host bacteria.
C) carry plasmids.
D) kill human cells.
E) kill the bacteria, causing release of endotoxins.

Question 41

Some pathogens evade phagocytosis, while other pathogens evade host defenses by entering host cells. Discuss the advantages and disadvantages of both of these evasion strategies.

Question 42

Antibiotics can kill gram-negative bacteria, but symptoms of fever and low blood pressure can persist. Why?

Question 43

Infections with some viruses may induce chromosomal changes that alter the growth properties of host cells.

Question 44

In general, the LD50 for exotoxins is much greater than the LD50 for endotoxins.

Question 45

Nonpathogenic Vibrio cholerae can acquire the cholera toxin gene by

A) infecting a pathogenic Vibrio cholerae.
B) transduction.
C) transformation.
D) conjugation.
E) phagocytosis.

Question 46

Many pathogens use the same portal for entry and exit from the body.

Question 47

In response to the presence of endotoxin, phagocytes secrete tumor necrosis factor. This causes

A) a gram-negative infection.
B) an increase in red blood cells.
C) the disease to subside.
D) a decrease in blood pressure.
E) a fever.

Question 48

Ergot and aflatoxin are toxins sometimes found in grains contaminated with fungi.

Question 49

Cytopathic effects, such as inclusion bodies and syncytium formation, are the visible signs of viral infections.

Question 50

The M protein enhances the virulence of Streptococcus by preventing phagocytosis.

Question 51

Table 15.2 $\begin{array}{|l|c|}\hline \text { Bacterium } & \text { ID50 } \\\hline \text { E. coli } 0157: \mathrm{H7} & 20 \\\hline \text { Legionella pneumophia } & 1 \\\hline \text { Shigella } & 10 \\\hline \text { Treponema pallidum } & 57 \\\hline\end{array}$

-Which organism in Table 15.2 causes the most severe disease?

A) E. coli O157:H7
B) Treponema pallidum
C) Shigella
D) Legionella pneumophila
E) It cannot be determined from the information provided.

Question 52

The Limulus amoebocyte assay is used to detect minute amounts of endotoxin in drugs and medical devices.

Question 53

Most symptoms of endotoxins can be treated with administration of anti-endotoxin antibodies.

Question 54

Patients developed inflammation a few hours following eye surgery. Instruments and solutions were sterile, and the Limulus assay was positive. The patientsʹ inflammation was due to

A) bacterial infection.
B) exotoxin.
C) endotoxin.
D) viral infection.
E) The answer cannot be determined based on the information provided.

Question 55

Biofilms provide pathogens with an adhesion mechanism and aid in resistance to antimicrobial agents.

Question 56

Bacteria that cause periodontal disease have adhesins for receptors on streptococci that colonize on teeth. This indicates that

A) streptococci get bacterial infections.
B) bacteria that cause periodontal disease adhere to gums and teeth.
C) streptococcal colonization is necessary for periodontal disease.
D) streptococci cause periodontal disease.
E) bacteria that cause periodontal disease adhere to teeth.

Question 57

In A-B exotoxins, the A component binds to the host cell receptor so that the B component can enter the cell.

Question 58

Compare and contrast endotoxins and exotoxins. Why are exotoxins more potent than endotoxins?