ch. 15

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Chapter 15
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1) The most frequently used portal of entry for pathogens is the

A) mucous membranes of the respiratory tract.

B) mucous membranes of the gastrointestinal tract.

C) skin.

D) parenteral route.

E) All of these portals are used equally.

Answer: A


2) The ability of some microbes, such as Trypanosoma or Giardiato alter their surface molecules and evade destruction by the hosts antibodies is called

A) antigenic variation.

B) lysogenic conversion.

C) virulence.

D) cytopathic effect.

E) cytocidal effect.

Answer: A


3) Most pathogens that gain access through the skin

A) can penetrate intact skin.

B) just infect the skin itself.

C) enter through hair follicles and sweat ducts.

D) must adhere first while their invasive factors allow them to penetrate.

E) must be injected.

Answer: C


4) The ID50 is

A) a measure of pathogenicity.

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) the dose that will cause an infection in some of the test population.

E) the dose that will kill 50 percent of the test population.

Answer: B


5) All of the following contribute to a pathogens invasiveness EXCEPT

A) toxins.

B) capsules.

C) cell wall components.

D) hyaluronidase.

E) coagulases.

Answer: A


6) Which of the following statements is FALSE?

A) Leukocidins destroy neutrophils.

B) Hemolysins lyse red blood cells.

C) Hyaluronidase breaks down substances between cells.

D) Kinase destroys fibrin clots.

E) Coagulase destroys blood clots.

Answer: E


7) Which of the following statements about exotoxins is generally FALSE?

A) They are more potent than endotoxins.

B) They are composed of proteins.

C) They are resistant to heat.

D) They have specific methods of action.

E) They are produced by gram-positive bacteria

Answer: C


8) Endotoxins are

A) associated with gram-positive bacteria.

B) molecules that bind nerve cells.

C) part of the gram-negative cell wall.

D) excreted from the cell.

E) A-B toxins.

Answer: C


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

A) A-B toxin

B) hemolysin

C) leukocidin

D) streptolysin O

E) streptolysin S

Answer: A


10) Cytopathic effects are changes in host cells due to

A) viral infections.

B) protozoan infections.

C) fungal infections.

D) bacterial infections.

E) helminthic infections.

Answer: A


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

A) capsules

B) toxins

C) allergic response of the host

D) cell walls

E) metabolic products

Answer: D


12) All of the following are methods of avoiding host antibodies EXCEPT

A) antigenic changes.

B) IgA proteases.

C) invasins.

D) membrane-disrupting toxins.

E) inducing endocytosis.

Answer: D


13) Siderophores are bacterial proteins that compete with the hosts

A) antibodies.

B) red blood cells.

C) iron-transport proteins.

D) white blood cells.

E) receptors.

Answer: C


14) 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.

Answer: D


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

A) injection.

B) bite.

C) surgery.

D) hair follicle.

E) skin cut.

Answer: D


16) Superantigens produce intense immune responses by stimulating lymphocytes to produce

A) endotoxins.

B) exotoxins.

C) cytokines.

D) leukocidins.

E) interferons.

Answer: C


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

A) boiling food prior to consumption.

B) administering antibiotics to patients.

C) not eating canned food.

D) preventing fecal contamination of food.

E) filtering food.

Answer: A


18) All of the following organisms produce exotoxins EXCEPT

A) Salmonella typhi.

B) Clostridium botulinum.

C) Corynebacterium diphtheriae.

D) Clostridium tetani.

E) Staphylococcus aureus.

Answer: A


19) Which of the following cytopathic effects is cytocidal?

A) inclusion bodies

B) giant cells

C) antigenic changes

D) transformation

E) release of enzymes from lysosomes

Answer: E


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

A) M protein.

B) ligands.

C) fimbriae.

D) capsules.

E) A-B toxins.

Answer: E


21) Symptoms of protozoan and helminthic diseases are due to

A) tissue damage due to growth of the parasite on the tissues.

B) waste products excreted by the parasite.

C) products released from damaged tissues.

D) tissue damage due to growth of the parasite on the tissues and waste products excreted by the parasite.

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

Answer: E


22) Which of the following statements about staphylococcal enterotoxin is FALSE?

A) It causes vomiting.

B) It causes diarrhea.

C) It is an exotoxin.

D) It is produced by Staphylococcus aureus growing in the hosts intestines.

E) It is a superantigen.

Answer: D


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

A) numbers of microorganisms that gain access to a host

B) evasion of host defenses

C) toxin production

D) numbers of microorganisms that gain access to a host and evasion of host defenses

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

Answer: E


24) Lysogenic bacteriophages contribute to bacterial virulence because bacteriophages

A) give new gene sequences to the host bacteria.

B) produce toxins.

C) carry plasmids.

D) kill the bacteria, causing release of endotoxins.

E) kill human cells.

Answer: A


25) 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) botulinum toxin.

B) aflatoxin.

C) staphylococcal enterotoxin.

D) erythrogenic toxin.

E) cholera toxin.

Answer: D


26) Which of the following statements about M protein is FALSE?

A) It is found on Streptococcus pyogenes.

B) It is found on fimbriae.

C) It is heat- and acid-resistant.

D) It is readily digested by phagocytes.

E) It is a protein.

Answer: D


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

A) A-B toxins.

B) lipid A.

C) membrane-disrupting toxins.

D) superantigens.

E) erythrogenic toxin.

Answer: D


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

A) the uncontrolled muscle contractions in Clostridium tetaniinfection

B) the invasion and lysis of intestinal cells by E. coli

C) the hemolysis of red blood cells in a staphylococcal infection

D) the fever, nausea, and low blood pressure in a Salmonellainfection

E) the excessive secretion of fluids in a Vibrio cholera infection

Answer: B


29) 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

Answer: C


30) All of the following bacteria release endotoxin EXCEPT

A) Clostridium botulinum.

B) Salmonella typhi.

C) Neisseria meningitidis.

D) Proteus vulgaris.

E) Haemophilus influenzae.

Answer: A


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

A) polypeptide A would bind to target cells.

B) polypeptide A would enter the cells.

C) polypeptide B would not be able to enter the cells.

D) Vibrio would not produce cholera toxin.

E) Vibrio would bind to target cells.

Answer: C


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

A) release TNF.

B) produce iron-binding proteins.

C) engulf the bacteria.

D) destroy the bacteria.

E) release cytokines.

Answer: C


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

A) producing fimbriae

B) inducing endocytosis

C) producing toxins

D) inducing TNF

E) antigenic variation

Answer: D


34) Injectable drugs are tested for endotoxins by

A) the Limulus amoebocyte lysate test.

B) counting the viable bacteria.

C) filtering out the cells.

D) looking for turbidity.

E) culturing bacteria.

Answer: A


35) Endotoxins in sterile injectable drugs could cause

A) infection.

B) septic shock symptoms.

C) giant cell formation.

D) nerve damage.

E) no damage, because they are sterile.

Answer: B


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

A) Body temperature is reset in the hypothalamus.

B) Fever occurs.

C) IL-1 is released.

D) LPS is released from gram-negative bacteria.

E) Phagocytes ingest gram-negative bacteria.

Answer: D


37) Antibiotics can lead to septic shock if used to treat

A) viral infections.

B) gram-negative bacterial infections.

C) gram-positive bacterial infections.

D) protozoan infections.

E) helminth infestations.

Answer: B


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

A) cell death

B) host cells fusing to form multinucleated syncytia

C) inclusion bodies forming in the cytoplasm or nucleus

D) increased cell growth

E) toxin production

Answer: E


39) Table 15.1


Portal of Entry

ID 50

Staphylococcus aureus



Staphylococcus aureus

Wound + Ampicillin


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

A) decreases the risk of staphylococcal infection.

B) increases the risk of staphylococcal infection.

C) has no effect on risk of infection.

D) replaces tetracycline.

E) The answer cannot be determined based on the information provided.

Answer: A



ID 50

E. coli O157:H7


Legionella pneumophila




Treponema pallidum


40) Which organism in Table 15.2 most easily causes an infection?

A) E. coli O157:H7

B) Legionella pneumophila

C) Shigella

D) Treponema pallidum

E) The answer cannot be determined based on the information provided.

Answer: B


41) Which organism in Table 15.2 causes the most severe disease?

A) E. coli O157:H7

B) Legionella pneumophila

C) Shigella

D) Treponema pallidum

E) It cannot be determined from the information provided.

Answer: E


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

A) streptococci get bacterial infections.

B) streptococcal colonization is necessary for periodontal disease.

C) bacteria that cause periodontal disease adhere to gums and teeth.

D) bacteria that cause periodontal disease adhere to teeth.

E) streptococci cause periodontal disease.

Answer: B


43) Nonpathogenic Vibrio cholerae can acquire the cholera toxin gene by

A) phagocytosis.

B) transduction.

C) conjugation.

D) transformation.

E) infecting a pathogenic Vibrio cholerae.

Answer: B


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

A) the disease to subside.

B) a decrease in blood pressure.

C) a fever.

D) a gram-negative infection.

E) an increase in red blood cells.

Answer: B


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

A) bacterial infection.

B) viral infection.

C) endotoxin.

D) exotoxin.

E) The answer cannot be determined based on the information provided.

Answer: C


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

Answer: FALSE


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

Answer: TRUE


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

Answer: TRUE


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

Answer: FALSE


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

Answer: TRUE


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

Answer: TRUE


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

Answer: TRUE


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

Answer: FALSE


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

Answer: TRUE


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

Answer: TRUE