Wk 1 Antibiotic Resistance

Question 1

What are 4 antibiotic resistance mechanisms?

Answer 1

1. Restrict antibiotic access - drug can’t get in or gets pumped out before affecting target - occurs in Gram-negative due to cell wall structure
2. Modify antibiotic target - structurally alterered or overexpressed, needing more drug - common in Gram-positive. Ex. Enzyme antibiotic would bind changes form
3. modification of the antibiotic - drug inactivated before affecting drug
4. modify expression of bacterial factors needed to activate the antibiotic (prodrugs)

Question 2

MRSA

Answer 2

=Methicillin resistant Staphylococcus aureus

-natural habitat = mucosal surfaces and skin
-resistance by modified target - mecA gene encodes PBP2a
-Gram-positive cocci

Question 3

2 target modification examples

Answer 3

MRSA
Vancomycin-resistant Enterococcus (VRE)

Question 4

VRE

Answer 4

• Enterococcus species – Gram positive cocci in pairs or
  chains
• Commensal in human intestines
• Bacteremia, intra-abdominal infections, UTIs
• VRE – Vancomycin resistant Enterococcus
• Modified Target
  – Plasmid-associated VanA gene

Question 5

Examples of modification of the antibiotic

Answer 5

beta-lactamases -> penicillin resistance by inactivating modification

Question 6

Examples of modification of the antibiotic

Answer 6

beta-lactamases -> penicillin resistance by inactivating modification
-one method of overcoming this resistance is to include beta-lactamase inhibitors

Question 7

Can resistance genes be shared between bacteria?

Answer 7

Yes. Not every bacteria develops new methods of resistance. They are shared and transferred between types of bacteria.

Question 7

Can resistance genes be shared between bacteria?

Answer 7

Yes. Not every bacteria develops new methods of resistance. They are shared and transferred between types of bacteria.

Question 8

What are 3 modes of transferring resistance genes?

Answer 8

1. conjugation
2. transformation
3. transduction - sharing of plasmids b/w bacteria - most common

Question 9

How do biofilms affect antibiotic treatments?

Answer 9

Bacteria w/in biofilms are often protected from antibiotics.
-common with prosthetic joint infections or can occur with other implanted medical devices

Question 10

How is antibiotic resistance measured clinically?

Answer 10

Antibiotic susceptibility tests:
1. dilution tests: Broth macrodilution or automated Broth Microdilution, both offer MIC (min inhibitory concentration)
2. diffusion tests: Disk Diffusion Test (Bauer-Kirby prcedure) or E-test Method -> zone of inhibition -> MIC

Question 11

What is MIC?

Answer 11

=min inhibitory concentration of a particular antibiotic against a particlar bacteria
S= susceptible
I= intermediate
R=resistant