Chapter 14: Staphylococci

Question 1

What are the Gram stain and morphology characteristics of Staphylococcus?

Answer 1

Catalase-positive, Gram-positive cocci

Often seen in clusters resembling grape bunches.

Question 2

List three common species of Staphylococcus.

Answer 2

• Staphylococcus aureus (most pathogenic)
• Staphylococcus epidermidis (CoNS)
• Staphylococcus saprophyticus (UTIs)

Question 3

What is the main virulence factor associated with S. aureus?

Answer 3

Protein A: Binds Fc region of antibodies to prevent phagocytosis.

Question 4

Name two toxins produced by S. aureus and their effects.

Answer 4

• Enterotoxins: Cause food poisoning
• Toxic Shock Syndrome Toxin-1 (TSST-1): Causes toxic shock

Question 5

What are the common clinical infections caused by S. aureus?

Answer 5

• Skin infections (boils, impetigo)
• Scalded skin syndrome
• Toxic shock syndrome
• Food poisoning
• Osteomyelitis
• Pneumonia

Question 6

What type of infections are associated with S. epidermidis (CoNS)?

Answer 6

Nosocomial infections associated with foreign bodies like catheters and implants.

Question 7

What is the significance of S. saprophyticus in clinical settings?

Answer 7

Common in UTIs, especially in young females; significant even in low numbers if predominant in a urine culture.

Question 8

What test differentiates S. aureus from CoNS?

Answer 8

Coagulase test (positive in S. aureus).

Question 9

What is the novobiocin sensitivity result for S. saprophyticus?

Answer 9

Resistant.

Question 10

What does MRSA stand for?

Answer 10

Methicillin-Resistant Staphylococcus aureus.

Question 11

Differentiate between HA-MRSA and CA-MRSA.

Answer 11

• HA-MRSA: Hospital-acquired
• CA-MRSA: Community-acquired

Question 12

What is a critical testing method for detecting MRSA?

Answer 12

PCR for mecA gene (confers methicillin resistance).

Question 13

What does the D-zone test detect?

Answer 13

Inducible clindamycin resistance.

Question 14

True or False: S. epidermidis is primarily responsible for skin infections.

Answer 14

False.

Question 15

Fill in the blank: S. saprophyticus is commonly associated with _______.

Answer 15

UTIs.

Question 16

What are the primary reservoirs for S. aureus?

Answer 16

• Nares
• Axillae
• Pharynx
• Vagina
• Skin surfaces

Question 17

What infection control measures are used for MRSA?

Answer 17

• Contact isolation
• Handwashing
• Barrier protection