Microbiology MCQ – Staphylococcus aureus

Question 1

What is the recommended first-line therapy for Methicillin-Susceptible S. aureus (MSSA) infections?

Accepted Answer

Nafcillin

Answer

Vancomycin

Answer

Daptomycin

Answer

Linezolid

Question 2

What is the characteristic shape of Staphylococcus aureus cells?

Accepted Answer

Spherical (cocci)

Answer

Rod-shaped

Answer

Spiral

Answer

Square

Question 3

Which antibiotic is a first-line treatment for Methicillin-Resistant S. aureus (MRSA) infections?

Accepted Answer

Vancomycin

Answer

Penicillin

Answer

Cefazolin

Answer

Clindamycin

Question 4

Which of the following best describes the typical arrangement of Staphylococcus aureus cells?

Accepted Answer

Grape-like clusters

Answer

Chains

Answer

Pairs

Answer

Single

Question 5

For localized skin infections or nasal decolonization of S. aureus, which topical agent is commonly used?

Accepted Answer

Mupirocin

Answer

Vancomycin

Answer

Linezolid

Answer

Daptomycin

Question 6

Staphylococcus aureus is classified as which type of bacterium based on its Gram stain reaction?

Accepted Answer

Gram-positive

Answer

Gram-negative

Answer

Gram-variable

Answer

Acid-fast

Question 7

Which culture-based method for detecting S. aureus is selective for staphylococci due to its high salt concentration and is differential for mannitol fermentation?

Accepted Answer

Mannitol Salt Agar (MSA)

Answer

Baird-Parker Agar

Answer

CHROMagar™ Staph aureus

Answer

RAPID’Staph Medium

Question 8

What is the typical diameter of an individual Staphylococcus aureus cell?

Accepted Answer

0.5–1.5 µm

Answer

0.1–0.4 µm

Answer

2–5 µm

Answer

5–10 µm

Question 9

What is the characteristic color of Staphylococcus aureus colonies on Mannitol Salt Agar (MSA) if it ferments mannitol?

Accepted Answer

Yellow

Answer

Pink

Answer

Black

Answer

White

Question 10

Is Staphylococcus aureus generally considered motile?

Accepted Answer

No, it is non-motile

Answer

Yes, with flagella

Answer

Yes, with pili

Answer

It is motile only in liquid environments

Question 11

Staphylococcus aureus can cause food poisoning due to the production of which type of heat-stable toxins?

Accepted Answer

Staphylococcal enterotoxins

Answer

Alpha-toxins

Answer

Exfoliative toxins

Answer

TSST-1

Question 12

Does Staphylococcus aureus form spores?

Accepted Answer

No, it is non-spore-forming

Answer

Yes, endospores

Answer

Yes, exospores

Answer

Only under harsh conditions

Question 13

What is a key prevention strategy against Staphylococcus aureus infections recommended for personal hygiene?

Accepted Answer

Frequent hand washing with soap and water

Answer

Consuming antibiotics regularly

Answer

Avoiding all public spaces

Answer

Never touching doorknobs

Question 14

Which term describes Staphylococcus aureus's ability to grow in both the presence and absence of oxygen?

Accepted Answer

Facultative anaerobe

Answer

Obligate anaerobe

Answer

Obligate aerobe

Answer

Microaerophile

Question 15

Which of the following is an effective practice for preventing Staphylococcus aureus transmission in healthcare settings?

Accepted Answer

Using contact precautions like gowns and gloves for colonized patients

Answer

Routine fogging of disinfectant in patient rooms

Answer

Sharing personal protective equipment among staff

Answer

Allowing patients with MRSA to share rooms without separation

Question 16

Where is Staphylococcus aureus most commonly found as a commensal organism in humans?

Accepted Answer

Nasal passages

Answer

Stomach lining

Answer

Lungs

Answer

Kidneys

Question 17

What is the recommended duration of intravenous therapy for uncomplicated Staphylococcus aureus bloodstream infections?

Accepted Answer

Minimum 14 days

Answer

3–5 days

Answer

7–10 days

Answer

4–6 weeks

Question 18

Which enzyme produced by Staphylococcus aureus is characterized by its ability to facilitate blood clot formation?

Accepted Answer

Coagulase

Answer

Hyaluronidase

Answer

Lipase

Answer

Nuclease

Question 19

Which of the following is NOT a virulence factor expressed by Staphylococcus aureus?

Accepted Answer

Flagella

Answer

Adhesins

Answer

Toxins

Answer

Enzymes

Question 20

Which virulence factor in Staphylococcus aureus binds to the Fc region of IgG, inhibiting opsonization and phagocytosis?

Accepted Answer

Protein A

Answer

Alpha-toxin

Answer

Coagulase

Answer

Hyaluronidase

Question 21

Which test is positive for Staphylococcus aureus, indicating its ability to produce the enzyme catalase?

Accepted Answer

Catalase test

Answer

Indole test

Answer

Coagulase test

Answer

Methyl red test

Question 22

The superantigen TSST-1, produced by Staphylococcus aureus, is primarily responsible for causing which severe condition?

Accepted Answer

Toxic Shock Syndrome (TSS)

Answer

Pneumonia

Answer

Osteomyelitis

Answer

Septic Arthritis

Question 23

When Staphylococcus aureus is cultured on Blood Agar Medium, what characteristic is typically observed around the colonies?

Accepted Answer

Beta-hemolysis (clear zone)

Answer

No hemolysis

Answer

Alpha-hemolysis (greenish discoloration)

Answer

Gamma-hemolysis (incomplete clearing)

Question 24

What common skin infection caused by Staphylococcus aureus is characterized by honey-colored crusts and is common in children?

Accepted Answer

Impetigo

Answer

Boils

Answer

Cellulitis

Answer

Carbuncles

Question 25

What is the approximate percentage of people who harbor Staphylococcus aureus as a commensal organism in their nasal passages, skin, and mucous membranes without causing disease?

Accepted Answer

20–30%

Answer

Less than 10%

Answer

40–50%

Answer

Over 60%

Question 26

Which severe systemic infection caused by Staphylococcus aureus involves inflammation of the bone, often affecting long bones in children?

Accepted Answer

Osteomyelitis

Answer

Meningitis

Answer

Endocarditis

Answer

Septic Arthritis

Question 27

What is a significant concern regarding MRSA in hospitals?

Accepted Answer

It is resistant to many antibiotics and can cause severe infections in vulnerable patients.

Answer

It only causes mild infections.

Answer

It is easily treatable with common antibiotics.

Answer

It cannot spread easily.

Question 28

Staphylococcus aureus is famous for its resistance to which specific antibiotic, leading to a significant public health concern?

Accepted Answer

Methicillin

Answer

Penicillin

Answer

Amoxicillin

Answer

Ciprofloxacin

Question 29

As of the provided content, is there a commercially available vaccine for Staphylococcus aureus?

Accepted Answer

No, but research is ongoing.

Answer

Yes, widely available.

Answer

Yes, but only for high-risk groups.

Answer

It is currently in phase 3 clinical trials.

Question 30

When was Methicillin-Resistant S. aureus (MRSA) first identified?

Accepted Answer

1960s

Answer

1930s

Answer

1940s

Answer

1950s