Antibiotic resistance mechanisms

Question 1

What is the MIC?

Answer 1

lowest antimicrobial concentration that prevents visible growth

Question 2

What are S. pneumonia and viridans streptococci agar appearance? Gram (+)

Answer 2

alpha-hemolytic
-oral flora

Question 3

what are group A and group B streptococci agar appearance? Gram (+)

Answer 3

beta-hemolytic
-skin, pharynx, genitourinary

Question 4

what are enterococcus faecalis & faecium? Gram (+)

Answer 4

gamma-hemolytic
-gastrointestinal

Question 5

What are the two types of B-lactamases?

Answer 5

Serine beta-lactamases
Metallo-beta-lactamases (MBLs, zinc residue)

Question 6

What are EBSLs?

Answer 6

can hydrolyze narrow and extended spectrum B-lactam antibiotics
ex. CTX-M-15
-treat with carbapenems

Question 7

What are serine carbapenemases?

Answer 7

hydrolyze carbapenems
ex. KPC-1, KPC-2, KPC-3
treatment: B-lactam combos or Plazomycin, ervacycline, omadacycline

Question 8

What are metallo-B-lactamases?

Answer 8

Hydrolyze carbapenems
*broadest & can wipe out whole class
ex. NDM-1
treatment: aztreonam + ceftazidime/avibactam

Question 9

What are Cephalosporinases?

Answer 9

Inducible
Amp-C
Treatment : Cefepime, carbapenems

Question 10

What are OXA-type

Answer 10

Hydrolyze oxacillin, oxyimino B-lactams, carbapenems
OXA-48
treatment: Cefiderocol or sulbactam/durlobactam

Question 11

What is AmpC found in?

Answer 11

HECK-YES
Hafnia Alvei, Enterobacter cloacae, Citrobacter freundii, Klebsiella aerogenes, Yersinia Enterocolitica

Question 12

What genes are resistant to vancomycin?

Answer 12

VanA or VanB
-produces vancomycin-resistant enterococcus (VRE)