Lec 6: Agents of Skin Infection II (JERSE)

Question 1

Staphylococcus aureus

Answer 1

Beta hemolytic, Gram (+), Catalase (+), Coagulase (+)

Causes suppurative lesions

Question 2

S. epidermidis

Answer 2

Gamma hemolytic, Gram (+), Catalase (+), Coagulase (-)

Infectious in hospital setting, immunocompromised patients, and post-surgical patients with indwelling medical devices

Question 3

S. saprophyticus (sp)

Answer 3

Gram (+), Catalase (+), Coagulase (-)

Question 4

Catalase Test

Answer 4

Dip small inoculum of bacteria into H2O2, bubbling = positive
Staph = (+)
Strep = (-)

Question 5

Nosocomial infections

Answer 5

Infections acquired while in the hospital (i.e. MRSA)

Question 6

S. aureus Virulence Factors

Answer 6

Protein A - “Absorbs” antibodies, binds Fc portion
Catalase - degrades H2O2
Leukocidin - pore forming protein, attacks leukocytes
Ribotechoic Acid, Techoic Acid - Bind fibronectin (in ECM)
Coagulase - Converts fibrinogen to fibrin (clot forming, staph hides in “shell” of clotted blood cells)
Capsule
Hyaluronidase - Breaks down hyaluronic acid, eases movement through subcutaneous tissues
Cytotoxins

Question 7

S. aureus Cytotoxins

Answer 7

Alpha Hemolysin - toxic pore-former
Beta Toxin - hydrolyzes membrane phospholipids, aka sphingomyelinase C
Delta Toxin - Cytolytic, detergent-like action
Gamma Toxin - Pore-forming toxin, neutrophils and MacPs
Panton-Valentin Leukocidin (PVL) - Pore-forming toxin

Question 8

S. intermedius

Answer 8

Coagulase (+)

Common flora in dogs, so suspect in dog bites

Question 9

Exfoliatins

Answer 9

Cause: Bullous impetigo, scalded skin syndrome, staphylococcal scarlet fever
Serine proteases which break down desmosomes in the stratum granulosum of the epidermis

Question 10

Toxic Shock Syndrome

Answer 10

Clinical Features:
sudden onset of: fever, chills, vomiting, diarrhea, rash, muscle pain
later: hypotension, invasion of mucous membranes and other systems, desquamation
5% fatality
At Risk Persons: Menstruating Women, Women with barrier contraceptive device, people undergoing nasal surgery

Question 11

Pyoderma

Answer 11

Any skin that is pyogenic, high morbidity in deployed personnel

Question 12

Bacteriophage Typing

Answer 12

S. aureus strains carry lysogenic viruses (Types I, II, and III) and are immune to infection by their own virus. Placing viruses onto separate S. aureus colonies allows identification of S. aureus strains

Question 13

Vancomycin

Answer 13

Glycopeptide that binds to D-ala-D-ala residues of peptidoglycan precursors, inhibiting production of future peptidoglycans
Current recommended treatment for MRSA

Question 14

VRSA

Answer 14

Vancomycin Resistant Staph. Aureus
Strongly resistant to Vancomycin
Due to acquisition of vanA gene (acquired from Enterococcus)
PG precursor now contains D-ala-D-lactate

Question 15

VISA

Answer 15

Vancomycin Intermediate S. Aureus

Partially resistant to Vancomycin

Question 16

MRSA

Answer 16

Methicillin Resistant S. Aureus

Question 17

VRE

Answer 17

Vancomycin Resistant Enterococcus

Source of vanA gene for S. aureus

Question 18

Role of Biofilms in infections

Answer 18

Biofilms can cause irreversible adhesion to medical equipment, which when inserted into a patient can cause an infection
Consists of extracellular polymers, aiding adhesion and providing a structural matrix