ID Intro (lectures 1&2)

Question 1

Gram + (summary)

Answer 1

• appear purple on gram stain
• cocci & bacilli (cocci majority)
• thick peptidoglycan cell wall
• colony clustering-staphylococci form clusters
• streptococci and enterococci form chains
• catalase test: staph from strep
• coagulase test: staphylococcus aureus from coagulase negative staphylococcus

Question 2

Gram - (summary)

Answer 2

• appear pink/red on gram stain
• bacilli predominant pathogen
• lactose fermentation: identifies enterobacteriales from non-fermenting gram neg rods
• oxidase test helps distinguish between enteric vs non-enteric lactose fermentors

Question 3

Penicillin Binding Proteins

Answer 3

• important binding site for bacteria
• vital for cell wall synthesis, cell shape, and structural integrity
• binding site for B-lactams (penicillins, cephalosporins, cephamycins, carbapenems)
• one of biggest targets when thinking about bug-drug activity

Question 4

B lactamase (basic overview)

Answer 4

• enzymes that hydrolyze B-lactam ring by splitting amide bond (inactivates B-lactam drugs)

Question 5

ESBL (Ambler Class A)

Answer 5

• extended-spectrum B-lactamases
• CTX-M enzyme indicates ESBL
• most prevalent in e coli, klebsiella pneumoniae/oxytoca, and proteus mirabilis
• tx of choice: carbapenems (meropenem, imipenem, doripenem, ertapenem)
• piperacillin/tazobactam option for urinary source only

Question 6

Carbapenemase (Ambler Class A)

Answer 6

• resistance to whole B-lactam class
• KPC enzyme indicates carbapenemase resistant enterobacterales
• found in: K. pneumoniae, K oxytoca, E coli, E cloacae, E aerogenes, P mirabilis
• tx options:
  B-lactam w/ B-lactamase inhibitor (ceftazidime/avibactam, meropenem/vaborbactam, imipenem/cilastatin/relebactam)
  Non B lactam – these are broader options
  (plazomicin, eravacycline, omadacycline)

Question 7

Metallo-B-Lactamases (Ambler Class B)

Answer 7

• resistance to all B lactams except monobactams
• New Delhi MBL (NDM) indicates
• tx: –limited–not inhibited by any B lactamase inhibitors
  cefiderocol, aztreonam+ceftazidime/avibactam

Question 8

OXA-type (Ambler Class D)

Answer 8

• OXA-48 indicates this
• tx options: –extremely limited–
  cefiderocol, sulbactam/durlobactam

Question 9

Cephalosporinases (Ambler Class C)

Answer 9

• Amp-C
• inducable via chromosomally encoded Amp-C genes
• found in (HECK-YES) —> (Amp-C inducers)
• all B-lactams are AmpC inducers
  high susceptibility to AmpC hydrolysis (penicillin G, ampicillin, 1st gen cephalosporins, cefoxitin)
  low susceptibilty to AmpC hydrolysis (carbapenems)–stable against

Question 10

mecA gene

Answer 10

• resistance due to expression of mecA gene
• encodes for PBP2A – low affinity for B lactams–resistance
• mecA –> PBP2A –> MRSA
• staphylococcus aureus resistance to B-lactams

Question 11

VanA gene

Answer 11

• VRE - vanc resistance in enterococcus
• VanA or VanB gene show altered target site (inhibits cell wall synthesis, altering target site of vanc and produces vanc-resistant enterococcus)
• vanA & vanB = VRE
• tx: daptomycin or linezolid

Question 12

mecA gene presence tx options

Answer 12

• B-lactams that work: ceftaroline, ceftobiprole
• vancomycin, daptomycin, lineozlid

Question 13

vanA and vanB gene presence tx options

Answer 13

daptomycin or linzeolid

Question 14

ermB

Answer 14

• macrolide resistance in S pneumoniae
• aminoglycoside resistance in gram negatives

Question 15

PK/PD Aminoglycosides

Answer 15

• concentration dependent
• Predictive pk/pd parameter: peak/mic; AUC/MIC
• cidal

Question 16

PK/PD B-lactams

Answer 16

• time dependent
• T>MIC
• cidal
• carbapenems >/= 40% fT/MIC
• penicillins >/= 50% fT/MIC
• cephalosporins >/=60% fT/MIC

Question 17

PK/PD Daptomycin

Answer 17

• concentration dependent
• AUC/MIC; peak/MIC
• cidal

Question 18

PK/PD Fluoroquinolones

Answer 18

• concentration dependent
• AUC(0-24)/MIC
• cidal

Question 19

PK/PD Vancomycin

Answer 19

• time-dependent
• AUC(0-24)/MIC
• cidal (slowly)