Methicillin-resistant Staph

Question 1

What is the main mechanism of methicillin-resistance in Staph sp?
A. Beta-lactamase enzyme that resists degradation by all beta-lactam antibiotics
B. Alteration of peptidoglycan binding site reducing affinity of all beta-lactam antibiotics
C. Production of PBP2a, a non-native PBP that resists all beta-lactam antibiotics
D. Presence of Panton-Valentine Leukocidin (PVL) toxin that degrades all beta-lactam antibiotics

Answer 1

C. Production of PBP2a, a non-native PBP that resists all beta-lactam antibiotics

Question 2

Genes that encode methicillin-resistance in Staphylococcus sp are shared by horizontal transmission of mobile genetic elements by what mechanism?
A. Bacteriophage
B. Staphylococcal chromosome cassette
C. Plasmid
D. Transposons

Answer 2

B. Staphylococcal chromosome cassette

Question 3

Which subtype of methicillin-resistant Staphylococcus sp is most important in the equine community?
A. MRSA USA 100
B. MRSA USA 300
C. MRSA USA 400
D. MRSA USA 500

Answer 3

D. MRSA USA 500

Question 4

In human cases, which of the following is a more common finding in community associated methicillin resistant staphylococcus (CA-MRSA) than Hospital associated methicillin resistant strains (HA-MRSA)
A. Presence of Panton-Valentine Leukocidin (PVL) toxin
B. Vancomycin resistance
C. Inducible Clindamycin resistance
D. Trimethoprim-sulfa antibiotic resistance

Answer 4

A. Presence of Panton-Valentine Leukocidin (PVL) toxin

Question 5

Name 3 methicillin-resistant Staphylococcal species

Answer 5

S pseudintermedius, S schleferi, S hyicus

Question 6

How does penicillin and other beta-lactam ring antibiotics work on bacteria?

Answer 6

They inactivate penicillin binding protein (PBP) which are essential for building the bacterial cell wall –> osmotic lysis of bacteria

Question 7

Name the gene that results in methicillin resistance

Answer 7

MecA gene

Question 8

What does the methicillin resistance gene code for?

Answer 8

The mecA gene codes for production of PBP2a, a non-native PBP

Question 9

T/F

Presence of PBP2a confers complete resistance to all beta-lactam antibiotics

Answer 9

True

Question 10

Where is the mecA gene located?

Answer 10

Staphylococcal chromosome cassette mec (SCCmec)

Question 11

What is Staphylococcal chromosome cassette mec (SCCmec)?

Answer 11

A mobile gene cassette that can be transferred horizontally between Staphylococcus

Question 12

What is the method used to classify MRSA?

Answer 12

Pulse field gel electrophoresis (PFGE)

Question 13

What is the most common HA (hospital assoc)-MRSA?

Answer 13

USA100 and USA200

Question 14

What is the most common CA (community assoc)-MRSA?

Answer 14

USA300

Question 15

What is the D-zone test?

Answer 15

Double disk diffusion D-zone test is for inducible clindamycin resistance

Question 16

What strain of MRSA most often has inducible clindamycin resistance?

Answer 16

HA-MRSA

Question 17

Which subtype of MRSA has more tissue damage?

Answer 17

CA-MRSA

Question 18

What is Panton-Valentine Leukocidin exotoxin?

Answer 18

PVL is a cytotoxin that forms pores that penetrate cell membranes causing osmotic lysis of leukocytes and tissue necrosis
Classic “spider-bite” appearance
Rapid forming cutaneous abscess, cellulitis, or furunculosis

Question 19

T/F

HA-MRSA causes more tissue damage but is resistant to fewer non-beta lactam antibiotics than CA-MRSA

Answer 19

False

CA-MRSA causes more tissue damage but is resistant to fewer non-beta lactam antibiotics than HA-MRSA

Question 20

What SCCmec type is the equine MRSA?

Answer 20

Equine MRSA USA500 is SCCmec type IV (CA-MRSA)

Question 21

USA500 strain is most commonly highly resistant to what antibiotic?

Answer 21

Potentiated sulfa antibiotic

high frequency of use of TMS in equine practice

Question 22

What is the gold standard test for identification of MRSA?

Answer 22

PCR detection of mecA

Question 23

Latex agglutination test can be performed to detect what for MRSA?

Answer 23

PBP2a

Question 24

T/F

Community acquired strains tend to have less antimicrobial resistance

Answer 24

True

Typically community acquired strains are resistant to only beta-lactams and erythromycin