Select the false statement about normal microbiota.
a. They compete with pathogens.
b. They do not include potential pathogens.
c. They make vitamins for the host.
d. They train the immune system.
e. A disruption in their balance can lead to disease.

Indicate the true statements and then correct the false statements so that they are true.

a. HIV is transmitted by a parenteral route.

b. Candida albicans is an opportunistic pathogen that can cause disease in an immune-competent host if the normal microbiota are disrupted.

c. Gram-positive bacteria may produce endotoxin.

d. Siderophores help pathogens obtain calcium.

e. Emerging pathogens tend to exhibit expanded tropism.

f. The more toxic a substance is, the higher its LD₅₀.

g. Virulence is the ability of a microbe to cause disease.

h. Gram-negative bacteria may produce exotoxins.

Pili, fimbriae, and sialic acid binding factors are examples of ________, which are virulence factors that allow pathogens to ________ host tissues––an essential early step in pathogenesis. In contrast, flagella, collagenases, and coagulases tend to act as ________, which help pathogens spread deeper into host tissues.

Define the class of each listed exotoxin as type I, II, or III:

a. Superantigen

b. Hemolysins

c. Staphylococcus aureus enterotoxins that cause food poisoning

d. AB toxin

e. Membrane-damaging toxins

f. Phospholipases

What is a reservoir, and why can C. difficile use a fomite as an effective environmental reservoir?

Toxigenic microbes produce _______. A high ID₅₀ would suggest _______, and a low LD₅₀ would suggest _______.

Which of the following is true regarding tropism?

a. It is the preference of a pathogen for a given tissue.

b. It is constant for a given microbe.

c. It limits a pathogen to infecting only one host.

d. It is determined by portal of entry.

e. It is independent of host factors.