Staphylococci

Question 1

Is staphylococci Gram positive or Gram negative?

Does it stain purple or pink?

Answer 1

Gram-positive; stains purple

Question 2

Describe the shape & structure of staphylococci colonies under the microscope

Answer 2

Round; irregular grape-like clusters of cocci

Question 3

Is staphylococci catalase-positive or negative?

Answer 3

Catalase-positive

Question 4

Name a coagulase +ve species of staphylococci

Answer 4

Staph. Aureus

Question 5

Name a coagulase -ve species of staphylocci

Answer 5

Staph. Epidermidis

Question 6

Habitat of Staph. Aureus

Answer 6

Anterior nares, skin, perineum

Question 7

Haemolytic activity of Staph. Aureus

Answer 7

B-haemolysis

Question 8

Colour of Staph. Aureus colonies on CBA

Answer 8

Golden-yellow; mostly white

Question 9

Transmission of Staph. Aureus

Answer 9

1. Contact
   - direct - hands, skin, mucous
   - indirect - instruments, door handles, bedding
2. Airborne
   - shedding of cocci from infected site into atmosphere
   - Dust/squames

Question 10

Superficial infections caused by Staph. aureus? (x4)

Answer 10

Abscesses, conjunctivitis, wound infections, boils

Question 11

Symptoms/Diagnosis of Toxic Shock Syndrome (x4)

Answer 11

• fever (39deg)
• hypotension (b/p less than 90mmHg)
• Diffuse macular rash and desquamation
• More than 3 organ systems involved (liver/blood/renal/mucous membranes/GI/CNS)

Question 12

Cause of toxic shock syndrome

Answer 12

exotoxin - toxic shock syndrome toxin 1 (TSST-1) - e.g. of superantigen

Question 13

Deep infections caused by Staph. aureus? (x3)

Answer 13

1. Acute endocarditis - bacteria enters soft tissues and bloodstream during injections
2. Pneumonia
3. Septicaemia

Question 14

What type of pathogen is Staph. Epidermidis?

Answer 14

Opportunistic pathogen

Question 15

Infections caused by Staph. Epidermidis (x3)

Answer 15

Catheter-related sepsis
Infection of artificial joints
Urinary tract infections

Question 16

Name 2 virulence factors associated with attachment (adhesins)

Answer 16

1. Fibrinogen-binding (ClfA ClfB)
2. Collagen binding (CNA)
   - Extra-cellular matrix molecules are present on epithelial, endothelial surfaces as well as a component of blood clots
   - Elastin binding proteins (Ebps)

Question 17

Name some virulence factors associated with the evasion of host defences (x7)

Answer 17

1. Protein A (only for Staph. Aureus)
2. Proteases (V8)
3. Superantigens
4. Lipases, Phospholipases, Esterase
5. Gamma haemolysin (toxin) hlg & Leukocidin (PVL - Panton-Valentine Leukocidin)
6. Coagulase
7. Capsule

Question 18

Name 3 virulence factors associated with invasion/tissue penetration

Answer 18

1. Hemolysins (alpha-toxins)
2. Hyaluronidase
3. Staphylokinase (Fibrinolysin) - digests fibrin

Question 19

Treatment of Staphylococci (x6)

Answer 19

1. Flucloxacillin (Methicillin) - class of penicillin stable against B-lactamase
2. Erythromycin - for patients allergic to the penicillin class
3. Vancomycin - treatments for MRSA
4. Linezolid - treatments for VRSA
5. Fusidic acid - Useful for skin infections
6. Mupirocin - topical decontamination

Question 20

Is penicillin useful in treating staphylococci infections?

Answer 20

no, 50-80% of staphylococci are resistant to penicillin