Question 1

Which of the following best explains why Methicillin-resistant Staphylococcus aureus (MRSA) infections are particularly concerning in hospital settings?

Accepted Answer

MRSA is less likely to cause disease in healthy individuals but can cause severe infections in immunocompromised patients due to its resistance to multiple antibiotics.

Question 2

A patient develops a rapidly spreading, necrotic wound after a traumatic injury. Laboratory tests reveal a Gram-positive, spore-forming, obligate anaerobe. Which organism is most likely responsible?

Accepted Answer

Clostridium perfringens

Question 3

Which of the following best describes the principle of serology in microbiology?

Accepted Answer

Serology identifies specific antigens or antibodies in blood by observing agglutination or binding reactions.

Question 4

A newborn develops a severe infection shortly after birth. The infection is traced to the mother, who had a recent untreated sore throat. Which pathogen is most likely responsible for the newborn's illness?

Accepted Answer

Streptococcus pyogenes

Question 5

Which of the following is a major virulence factor of Staphylococcus aureus that can cause scalded skin syndrome (SSSS)?

Accepted Answer

Exfoliative toxin

Question 6

A patient presents with a chronic cough and weight loss. Laboratory tests confirm Mycobacterium tuberculosis infection. Which factor most significantly increases the risk of developing active tuberculosis after exposure?

Accepted Answer

Immunocompromised state (e.g., HIV infection)

Question 7

Which of the following best explains why Clostridium botulinum toxin is dangerous even after the bacteria are killed by cooking?

Accepted Answer

The toxin is heat-stable and can remain active if not destroyed by proper heating.

Question 8

Which of the following is a common method for identifying different strains of Staphylococcus aureus in a clinical laboratory?

Accepted Answer

Phage typing

Question 9

A patient with a burn wound develops a greenish pus and a fruity odor at the site. The causative organism is a Gram-negative rod known for its resistance to many antibiotics. Which organism is most likely responsible?

Accepted Answer

Pseudomonas aeruginosa

Question 10

Which of the following best describes the role of the capsule in bacterial pathogenicity?

Accepted Answer

It helps bacteria evade phagocytosis by host immune cells.

Question 11

Which of the following statements about Streptococcus pyogenes is correct?

Accepted Answer

It is a Group A beta-hemolytic streptococcus that can cause diseases such as strep throat, scarlet fever, and rheumatic fever.

Question 12

A patient is diagnosed with toxic shock syndrome (TSS). Which of the following best explains the pathogenesis of this condition?

Accepted Answer

Production of a superantigen toxin that causes massive, non-specific activation of T cells and cytokine release.

Question 13

Which of the following laboratory techniques is most appropriate for distinguishing between different species of bacteria based on their DNA sequences?

Accepted Answer

Polymerase Chain Reaction (PCR)

Question 14

A patient with a history of intravenous drug use presents with fever and a new heart murmur. Blood cultures grow Streptococcus pyogenes. Which serious complication is most likely to develop?

Accepted Answer

Rheumatic fever with possible heart valve damage

Question 15

Which of the following best explains why populations with higher exposure to Mycobacterium tuberculosis tend to have more resistant strains over time?

Accepted Answer

Natural selection favors strains that survive antibiotic treatment and host immunity.

Question 16

Which of the following is the most likely reason why Clostridium difficile infections are common in hospitalized patients after antibiotic treatment?

Accepted Answer

Antibiotics disrupt the normal gut flora, allowing C. difficile to proliferate.

Question 17

Which of the following best describes the use of ELISA in clinical microbiology?

Accepted Answer

It detects the presence of specific antigens or antibodies in a patient's serum.

Question 18

A patient with a severe burn is at increased risk for infection by which of the following bacteria, known for its resistance to disinfectants and ability to grow in moist environments?

Accepted Answer

Pseudomonas aeruginosa

Question 19

Which of the following is a key difference between exotoxins and endotoxins?

Accepted Answer

Exotoxins are secreted proteins that can cause disease even in the absence of bacteria, while endotoxins are components of the bacterial cell wall released upon cell death.

Question 20

Which of the following best explains why some populations have lower rates of tuberculosis despite similar exposure levels?

Accepted Answer

Genetic susceptibility and differences in immune response can influence infection rates.

Microbiology Study Notes: Bacterial Pathogens, Disease Mechanisms, and Laboratory Identification

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