U E S T I O N S

11. How can shigellas move from one host cell to another even though they are non-motile?

12. Name four different groups of Escherichia coli based on their pathogenic mechanisms.

13. Contrast the transmission of hepatitis A and hepatitis B.

14. Name two kinds of hepatitis that can be prevented by vaccines.

15. Contrast the cause and epidemiology of giardiasis and amebiasis.

16. Give two characteristics of Cryptosporidium parvum that allow it to contaminate municipal water supplies.

Multiple Choice

1. The following are all true of intestinal bacteria, except

A. they produce vitamins.

B. they can produce carcinogens.

C. they are mostly aerobes.

D. they produce gas from indigestible substances in foods.

E. they include potential pathogens.

Chapter 24 Alimentary System Infections

2. All of the following attributes of Streptococcus mutans are important in tooth decay, except

A. it attaches specifically to tooth pellicle.

C. it produces lactic acid.

D. it synthesizes glucan.

E. it stores fermentable polysaccharide.

3. All of the following are true of Helicobacter pylori, except

A. it is a helical bacterium with sheathed flagella.

B. it has not been cultivated in vitro.

C. it produces a powerful urease.

D. it causes stomach infections that last for years.

E. it has an important role in the causation of stomach ulcers.

4. All of the following are probably important to the cholera-causing ability of Vibrio cholerae, except

A. it attaches firmly to small intestinal epithelium.

B. it produces cholera toxin.

C. lysogenic conversion.

D. acid resistance.

E. it survives in the sea in association with zooplankton.

5. Pick out which one of the following statements concerning Salmonella Typhi is false:

A. It is commonly acquired from domestic animals.

B. It can colonize the gallbladder for years.

C. It is highly resistant to killing by bile.

D. It can destroy Peyer's patches.

E. It causes typhoid fever.

6. One of the subsequent five statements about rotaviral gastroenteritis is false. Which one?

A. The name of the causative agent was suggested by its appearance.

B. Most of the 600,000 deaths occurring worldwide from this disease are due to dehydration.

C. Most cases of the disease occur in infants and children.

D. The causative agent infects mainly the stomach.

E. The disease is transmitted by the fecal-oral route.

7. Which of the following statements about Norwalk viruses is false?

A. They cause almost half the cases of viral gastroenteritis in the United States.

B. They can be responsible for epidemics of gastroenteritis.

C. They generally produce an illness lasting 1 to 2 weeks.

D. Similar viruses are widespread among marine animals.

E. They typically cause disease in children and adults rather than infants.

8. Which of the following statements about hepatitis is false?

A. Both RNA and DNA viruses can cause hepatitis.

B. Some kinds of hepatitis can be prevented by vaccines.

C. More than half of the new hepatitis C cases are the result of injected-drug abuse.

D. Lifelong carriers of hepatitis A are common.

E. At least six different viruses can cause hepatitis.

9. Which of the following statements about hepatitis B virus is false?

A. Replication involves reverse transcriptase.

B. Infected persons may have large numbers of non-infectious viral particles circulating in their bloodstream.

C. In the United States the incidence of infection has been steadily increasing over the last few years.

D. Asymptomatic infections can last for years.

E. Infection can result in cirrhosis.

10. Choose the most accurate statement about cryptosporidiosis.

A. Waterborne transmission is unlikely.

B. The host range of the causative agent is narrow.

C. It is prevented by chlorination of drinking water.

D. Person-to-person spread does not occur.

E. The life cycle of the causative agent occurs within small intestinal epithelial cells.

Applications

1. An international health commission has been asked to judge whether mumps virus or herpes simplex virus should be the next target for elimination from the world. What should they advise, and what facts should they take into account in making their decision?

2. One reason given by Peruvian officials for not chlorinating their water supply was that chlorine can react with substances in water or the intestine to produce carcinogens. How do you assess the relative risks of chlorinating or not chlorinating drinking water?

3. A medical scientist is designing a research program to determine the effectiveness of hepatitis B vaccine in preventing liver cell cancer. Since liver cell cancer probably has multiple causes, how would you measure the success of an anticancer vaccination program?

4. An official at the Centers for Disease Control and Prevention noticed that the annual rate of new hepatitis C virus infections, which averaged 230,000 during the 1980s, had dropped to

36,000 by 1996. What did she determine were the probable reasons for this dramatic change?

Critical Thinking

1. What might the lack of a brown color of feces indicate?

2. Mutant strains of Helicobacter pylori that lack the ability to produce urease fail to cause infection when they are swallowed. Infection occurs, however, if a tube is used to introduce them directly into the layer of mucus that overlies the stomach epithelium. What does this imply about the role of urease in the bacterium's pathogenicity?

3. Mutant strains of Vibrio cholerae can be isolated that fail to produce cholera. A microbiologist postulated that a defect in either the A or the B portion of cholera toxin could explain the lack of virulence. Is the microbiologist's explanation reasonable? Why or why not?

4. Looking at the replication cycle of hepatitis B virus (see figure 24.20), a student wondered whether core protein might be necessary for the assembly of viral envelope. What observation supports or refutes this idea?

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