Question 1

A patient is exposed to two different bacterial strains. Strain A has an LD$$_{50} of$$ $$10^3$$ cells, while Strain B has an LD$$_{50} of$$ $$10^7$$ cells. Which statement best describes the relative virulence of these strains?

Accepted Answer

Strain A is more virulent because it has a lower LD$$_{50}.$$

Question 2

Which of the following best explains how bacterial capsules contribute to pathogenicity?

Accepted Answer

They prevent phagocytosis by host immune cells.

Question 3

A patient receives a mismatched blood transfusion and develops hemolysis. Which type of hypersensitivity reaction is this, and what is the underlying mechanism?

Accepted Answer

Type II; IgG or IgM antibodies binding to cell surface antigens

Question 4

Which of the following enzymes allows bacteria to break down connective tissue and spread through host tissues?

Accepted Answer

Hyaluronidase

Question 5

A patient develops a rash and joint pain several days after receiving antiserum. Laboratory tests reveal immune complexes in the tissues. Which hypersensitivity type is most likely responsible?

Accepted Answer

Type III (Immune Complex)

Question 6

Which of the following statements about exotoxins and endotoxins is correct?

Accepted Answer

Exotoxins are proteins that can be neutralized by antitoxins.

Question 7

Which of the following best describes the role of biofilms in microbial pathogenicity?

Accepted Answer

Biofilms protect bacteria from host defenses and antibiotics.

Question 8

A patient with HIV is found to have a CD4$$^+ T $$cell count of 180 cells/$$\muL. $$Which stage of HIV infection does this most likely represent?

Accepted Answer

AIDS (Acquired Immunodeficiency Syndrome)

Question 9

Which of the following is a correct sequence of events in the nitrogen cycle involving microorganisms?

Accepted Answer

Nitrogen fixation $$\rightarrow$$ Ammonification $$\rightarrow$$ Nitrification

Question 10

A city is experiencing an outbreak of waterborne disease. Which step in the sewage treatment process is most critical for removing pathogenic microorganisms before water is released into the environment?

Accepted Answer

Secondary treatment

Question 11

Which of the following best describes the function of adhesins in bacterial pathogenicity?

Accepted Answer

They enable bacteria to attach to host cell receptors.

Question 12

A patient with a genetic deficiency in complement proteins is most likely to experience which of the following?

Accepted Answer

Increased susceptibility to bacterial infections

Question 13

Which of the following is an example of a Type IV (delayed cell-mediated) hypersensitivity reaction?

Accepted Answer

Contact dermatitis from poison ivy

Question 14

Which of the following best describes the relationship between humans and their gut microbiota?

Accepted Answer

Mutualism

Question 15

Which of the following is a major portal of exit for respiratory pathogens?

Accepted Answer

Saliva and respiratory droplets

Question 16

A patient with a history of multiple infections is found to have a defect in the HLA complex. Which of the following is most likely impaired?

Accepted Answer

Antigen presentation to T cells

Question 17

Which of the following best explains why secondary sewage treatment is essential for water quality?

Accepted Answer

It uses microbial activity to degrade organic matter.

Question 18

Which of the following is a characteristic property of endotoxins?

Accepted Answer

They are part of the lipopolysaccharide layer of Gram-negative bacteria.

Question 19

Which of the following best describes the role of microorganisms in the phosphorus cycle?

Accepted Answer

They release phosphate ions from organic matter during decomposition.

Question 20

A patient develops a severe, rapid-onset allergic reaction after eating peanuts, including difficulty breathing and hypotension. Which immunoglobulin and cell type are primarily responsible for this reaction?

Accepted Answer

IgE and mast cells

Microbiology Final Exam Review: Pathogenicity, Immune Disorders, and Environmental Microbiology

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