22. An important host defense of human beings is a dense resident microbiota associated with
23. Lactoferrin helps to protect against pathogens by
B.blocking sebum production
C.lowering the pH
D.facilitating the growth of normal flora
24. The influenza vaccine is administered each year because
A.mutations in the viral hemagglutinin may allow the virus to evade the immune response elicited by previous vaccines
B.it is a polysaccharide vaccine that does not confer long-term protection
C.he vaccine is sufficiently toxic to make it necessary to administer only a small amount at any one time
D.none of the above
25. Which of the following disease is caused by DNA viruses?
26. Which of the following is common in the disease caused by Coryne-bacterium diphtheriae and Bacillus anthracis?
A.Both organisms are gram-positive spore formers
B.Diphtheria toxin and edema toxin are ADP ribosylating toxins
C.The most serious disease symptoms are the direct result of toxin action
D.Both organisms cause skin and respiratory tract infections
27. Fatalities following influenza infection are usually due to the
C.damage to the heart muscle
D.formation of granulomas in the lung
28. Which of the following disease is not caused by microbial protein toxin?
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