Acquired resistance mechanisms

Question 1

mecA, mecC

Answer 1

PBP2A
Responsible for methicillin resistance in staph
mecA - most common in US and worldwide - cefoxitin is more sensitive for detection
mecC - found in Europe - oxacillin is more sensitive for detection

Resistance to all beta-lactams except ceftaroline

Question 2

VISA

Answer 2

Neither intrinsic nor acquired - genetic expression changes after exposure to vancomycin (eg. thickness of cell wall, etc.)

Question 3

vanA, vanB

Answer 3

Encode cell wall precursors that end in D-ala-D-lac instead of D-ala-D-ala

Seen in VRE, rarely VRSA

VanA - most common in US, resistant to teicoplanin
VanB - susceptible to teicoplanin

Question 4

ESBL

Answer 4

Mobile genetic elements
>900 types/variations
Most cause resistance to:
-PCNs
-1st-3rd gen cephalosporins, +/- 4th gen CPH
-High level expression can lead to resistance to ertapenem

Question 5

AmpC

Answer 5

Beta-lactamase

Can be acquired as well as chromosomal in SPICE organisms

Question 6

KPC

Answer 6

Serine (A) Carbapenemase

Most common in US

Found in Enterobacteriaceae and nonfermenters

Usually still susceptible to ceftazidime-avibactam, cefideracol, imipenem-relebactam, meropenem -vaborbactam

+mCIM/-eCIM

Question 7

OXA-48

Answer 7

Serine carbapenemase (D)
Usually susceptibilbe to ceftazidime-avibactam, cefideracol (but not Imi-rel or mero-vabor)

Some remain susceptible to cephalosporins while resistant to carbapenems

+mCIM/-eCIM

Question 8

NDM

Answer 8

Zinc metallocarbapenemase (B)

Susceptible to cefiderocol,
Aztreonam (may need avibactam), colisitn, tigecycline?

+mCIM/+eCIM

Question 9

VIM/IMP

Answer 9

Zinc (metallo) carbapenemase (B)

Susceptibile to colistin, tigecycline, ?aztreonam +avibactam?

+mCIM/+eCIM