B3.003 Intro to Lab Diagnosis of Infectious Disease: Clincial Cases

Question 1

functions of bacterial cell wall

Answer 1

structural rigidity
shape
osmoregulation
defense

Question 2

resistance mechanisms of bacteria to antimicrobial drugs

Answer 2

enzymatic inactivation- bacteria produce enzymes that inactivate drug
modification of target- bacteria produce alternate proteins
porin mutations- reduce permeability (gram -)
efflux pumps (gram -)

Question 3

components of peptidoglycan layer of gram + cell wall

Answer 3

glycan side chains 
- N-acetylglucoseamine (NAG)
- N-acetylmuramic acid (NAM)
tetrapeptide chain (variable amino acids)
peptide interbridge (cross linker)

Question 4

process of building a peptidoglycan layer

Answer 4

1. peptidoglycan polymers exported from cell
2. transglycosylase attaches polymers to chain
3. transpeptidase crosslinks polymers (penicillin binding protein (PBP))

Question 5

mechanism of action of B-lactam antimicrobials

Answer 5

structural mimic of tetrapeptide chain of NAM
bind the enzymatic domain of PBP
prevent peptide crosslinking, leading to weakened cell wall and death of bacteria by lack of osmoregulation

Question 6

enzymatic inactivation mechanism of resistance against B-lactams

Answer 6

synthesis of B-lactamase (cleaves/degrades ring)
ex: pinicillinase, carbapenemases, extended spectrum B-lactamases
gram + : secreted extracellularly
gram - : secreted into periplasmic space

Question 7

mechanism of resistance of methicillin resistant S.aureus

Answer 7

modification of target
staphylococci may acquire mecA gene cassette
mecA gene encodes PBP2a
PBP2a retains transpeptidase activity but has low affinity for penicillin