Question 1

Which of the following best explains why Staphylococcus aureus is able to survive on human skin and cause infections in moist areas?

Accepted Answer

It is salt tolerant and possesses enzymes such as coagulase and lipase that enhance survival and virulence.

Question 2

A patient presents with a rapidly progressing skin infection characterized by severe pain and tissue destruction. Laboratory tests reveal Gram-positive cocci in chains. Which pathogen is most likely responsible, and what is the most appropriate initial treatment?

Accepted Answer

Streptococcus pyogenes (Group A); treat with penicillin and surgical intervention if necrosis is present.

Question 3

Which of the following best describes the mechanism by which Clostridium difficile causes severe gastrointestinal disease after antibiotic therapy?

Accepted Answer

It forms endospores that survive in the environment and produces toxins that damage the intestinal lining when normal microbiota are disrupted.

Question 4

A newborn develops meningitis shortly after birth. The mother was not screened for Group B Streptococcus during pregnancy. Which of the following statements is correct regarding this pathogen?

Accepted Answer

It is a Gram-positive coccus that causes beta-hemolysis and is commonly found in the lower gastrointestinal and urogenital tracts.

Question 5

Which of the following best explains why methicillin-resistant Staphylococcus aureus (MRSA) is difficult to treat?

Accepted Answer

It produces beta-lactamase, which inactivates penicillin, and has acquired resistance to methicillin, often requiring vancomycin for treatment.

Question 6

A patient presents with fever, abdominal pain, and diarrhea after eating undercooked eggs. Laboratory tests identify motile Gram-negative bacilli with peritrichous flagella. Which pathogen is most likely responsible, and what is the primary treatment?

Accepted Answer

Salmonella enterica; treat with fluids and electrolytes.

Question 7

Which of the following statements about Bordetella pertussis is correct?

Accepted Answer

It binds to ciliated epithelial cells of the trachea using adhesins and produces toxins that disrupt cell metabolism and mucus production.

Question 8

A patient presents with a painless ulcer (chancre) on the genitals, followed weeks later by a widespread rash and flu-like symptoms. Which pathogen is responsible, and what is the recommended treatment for early infection?

Accepted Answer

Treponema pallidum; treat with intramuscular Benzathine penicillin G.

Question 9

Which of the following best explains why Borrelia burgdorferi infection (Lyme disease) can be prevented by removing ticks within 24 hours?

Accepted Answer

The bacterium requires at least 48 hours of tick attachment to be transmitted to the host.

Question 10

Which of the following statements about Hepatitis B virus (HBV) is correct?

Accepted Answer

It is an enveloped DNA virus that uses reverse transcriptase to replicate its genome.

Question 11

A child presents with fever, cough, and a paroxysmal 'whooping' cough. Which phase of Bordetella pertussis infection is most associated with the characteristic 'whoop' and what is the underlying cause?

Accepted Answer

Paroxysmal phase; due to impaired ciliary function and increased mucus production.

Question 12

Which of the following best describes the process of antigenic shift in influenza viruses?

Accepted Answer

A major change in the viral genome resulting from reassortment of genome segments when two different subtypes infect the same cell.

Question 13

A patient with HIV is monitored for disease progression. Which laboratory values are most important for tracking the transition to AIDS, and what is their relationship?

Accepted Answer

Viral load and CD4+ T cell count; as viral load increases, CD4+ T cell count decreases.

Question 14

Which of the following best explains why measles outbreaks can occur even in populations with high vaccination rates?

Accepted Answer

Measles is highly contagious and requires at least 95% vaccine coverage to prevent outbreaks.

Question 15

A patient presents with fever, cough, and a rapidly progressing pneumonia. Laboratory tests reveal a dimorphic fungus. Which of the following is most likely responsible, and what is a key feature of its life cycle?

Accepted Answer

Histoplasma capsulatum; grows as multicellular mycelia in the environment and as unicellular yeast in the body.

Question 16

Which of the following statements about Plasmodium species (malaria) is correct?

Accepted Answer

They replicate asexually in human liver and red blood cells, and sexually in mosquitoes.

Question 17

A pregnant woman is advised to avoid cleaning cat litter boxes and eating undercooked meat to prevent infection by which pathogen, and why is this important?

Accepted Answer

Toxoplasma gondii; it can cross the placenta and cause congenital infection.

Question 18

Which of the following best explains why the oral polio vaccine is no longer used in the United States?

Accepted Answer

It can rarely revert to a virulent form and cause vaccine-associated paralytic polio.

Question 19

A patient with AIDS develops a severe fungal infection after visiting the southwestern United States. Spherules are observed in a lung biopsy. Which pathogen is most likely responsible, and what is a key diagnostic feature?

Accepted Answer

Coccidioides immitis; presence of spherules in tissue.

Parade of Pathogens: Key Microbial Agents and Their Clinical Significance

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