Question 1

A patient presents with a severe sore throat, fever, and a grayish membrane covering the tonsils and pharynx. Which organism is most likely responsible, and what is the primary mechanism of its pathogenicity?

Accepted Answer

Corynebacterium diphtheriae; production of diphtheria toxin that inhibits protein synthesis ($	ext{inhibits EF-2}$)

Question 2

Which of the following best explains why Mycobacterium tuberculosis is resistant to many common antibiotics?

Accepted Answer

It possesses a waxy mycolic acid-rich cell wall that limits drug penetration.

Question 3

A 5-year-old child develops a sandpaper-like rash, strawberry tongue, and fever after a sore throat. Which bacterial virulence factor is most responsible for the rash?

Accepted Answer

Erythrogenic (pyrogenic) exotoxin

Question 4

A patient with a history of antibiotic use develops severe diarrhea and pseudomembranous colitis. Which organism is most likely responsible, and what is the recommended first-line treatment?

Accepted Answer

Clostridioides difficile; oral vancomycin

Question 5

Which of the following is the most common cause of bacterial pneumonia in adults, and what is a key feature seen on Gram stain?

Accepted Answer

Streptococcus pneumoniae; Gram-positive diplococci

Question 6

A patient presents with a bull's-eye rash after a tick bite and later develops arthritis. Which organism is responsible, and what is the recommended initial treatment?

Accepted Answer

Borrelia burgdorferi; doxycycline

Question 7

Which of the following statements about the pathogenesis of rheumatic fever is correct?

Accepted Answer

It results from an autoimmune response due to molecular mimicry between streptococcal antigens and human tissues.

Question 8

A 22-year-old college student develops a sudden high fever, stiff neck, and petechial rash. Which organism is most likely responsible, and what is the primary virulence factor?

Accepted Answer

Neisseria meningitidis; polysaccharide capsule

Question 9

Which of the following best describes the mechanism of action of the tetanus toxin produced by Clostridium tetani?

Accepted Answer

It inhibits the release of inhibitory neurotransmitters (GABA and glycine), leading to spastic paralysis.

Question 10

A patient develops hemolytic uremic syndrome (HUS) after eating undercooked ground beef. Which bacterial factor is most responsible for this complication?

Accepted Answer

Shiga-like toxin produced by E. coli O157:H7

Question 11

Which of the following is the most effective method for preventing neonatal herpes infection?

Accepted Answer

Performing a cesarean section if active genital lesions are present at delivery

Question 12

A patient presents with fever, jaundice, and renal failure after swimming in contaminated water. Which organism is most likely responsible?

Accepted Answer

Leptospira interrogans

Question 13

Which of the following best explains why the smallpox vaccine is effective at eradicating the disease?

Accepted Answer

The vaccine induces both humoral and cellular immunity, and humans are the only reservoir for the virus.

Question 14

A 30-year-old woman presents with thick, white, curd-like vaginal discharge and intense itching. Which organism is most likely responsible, and what is a common predisposing factor?

Accepted Answer

Candida albicans; recent antibiotic use

Question 15

Which of the following is a key distinguishing feature of Mycoplasma pneumoniae compared to other common causes of pneumonia?

Accepted Answer

It lacks a cell wall and is not visible on Gram stain.

Question 16

A patient develops acute glomerulonephritis two weeks after a streptococcal skin infection. Which immunological mechanism is primarily responsible?

Accepted Answer

Immune complex deposition in the glomeruli

Question 17

Which of the following best describes the pathogenesis of cholera?

Accepted Answer

Production of an enterotoxin that increases cAMP in enterocytes, leading to watery diarrhea ($	ext{cAMP} \uparrow$)

Question 18

A 7-year-old child develops a vesicular rash that starts on the face and spreads to the trunk. Which virus is responsible, and what is a potential complication in adults?

Accepted Answer

Varicella-zoster virus; shingles (herpes zoster)

Question 19

Which of the following is the most important preventive measure for rabies after a potential exposure (e.g., animal bite)?

Accepted Answer

Immediate administration of post-exposure prophylaxis (PEP) with rabies vaccine and immunoglobulin

Question 20

A patient with a history of chronic kidney disease develops a urinary tract infection with fever, flank pain, and white blood cell casts in the urine. Which organism is most likely responsible?

Accepted Answer

Escherichia coli

Comprehensive Study Guide: Infectious Diseases and Microbial Pathogens

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