Antimicrobial Resistance (Lec. 16)

Question 1

Distinguish between intrinsic and acquired antimicrobial resistance and provide an example of each.

Answer 1

Intrinsic or natural resistance is naturally occurring based on biological structures (cell wall composition, endospore formation, etc). Acquired resistance is a change in the genome of a microbe that converts it from one that is sensitive to an antibiotic to one that is resistant due to mutations or HGT.

Question 2

Describe the three mechanisms of HGT in bacteria

Answer 2

Conjugation: transfer of DNA from a donor bacterium to a recipient bacterium through direct cell-to-cell contact.
Transformation: a bacterium taking up DNA from the surrounding environment
Transduction: bacterial DNA is moved from one bacterium to another by a virus

Question 3

Identify the four mechanisms by which antibiotic resistance may develop

Answer 3

Modification of drug target (PBP2A and VRE). Enzymatic inactivation (beta-lactamase). Removal via efflux pumps (AcrAB-TolC of E. coli). Metabolic bypasses (biofilm growth).

Question 4

Describe the role of the PBP2A in the development of antimicrobial resistance.

Answer 4

Penicillin-binding protein 2a prevents beta-lactam antibiotics from inhibiting cell wall synthesis

Question 5

Describe the role of beta-lactamase in the development of antimicrobial resistance

Answer 5

Beta-lactamases inactivate beta-lactam antibiotics, making bacteria resistant to them.

Question 6

Describe the role of CAT in the development of antimicrobial resistance

Answer 6

Chloramphenicol acetyl transferase inactivates the antibiotic chloramphenicol, making bacteria resistant to it.

Question 7

Describe the role of efflux pumps in the development of antimicrobial resistance

Answer 7

Efflux pumps can remove a drug from a cell; they tend to remove diverse classes of drugs and contribute to multidrug resistance.

Question 8

Describe the mechanisms of antibiotic resistance that are seen in biofilms

Answer 8

Resistance at the biofilm surface: the diffusion of the drug through the biofilm is slow due to extracellular matrix. Resistance within biofilm microenvironments due to diverse metabolic byproducts, waste, and nutrients, and low O2 levels. Resistance of bacterial “persister” cells, which exist in a dormant state and do not divide.

Question 9

Define MRSA

Answer 9

Methicillin-resistant Staphylococcus aureus is resistant to all beta-lactams because it has PBP2A instead of PBP

Question 10

Define VRE

Answer 10

Vancomycin-resistant Enterococcus. A PG subunit normally has terminal D-Ala, but in VRE it has terminal D-lactate or D-serine.

Question 11

Identify the methods for detecting drug resistance in laboratory isolates.

Answer 11

Microbroth dilution; detection of specific resistance factors and specific resistance genes.