Antibiotic Resistance

Question 1

What are the main mechanisms for antibacterial resistance ?

Answer 1

• mutation of antibiotic target site
• antibiotic modifying enzymes
• antibiotic efflux/entry block

Question 2

Describe the mechanism of beta-lactam resistance through alteration of the target site

Answer 2

• mutation of penicillin binding proteins or through gene transfer (acquisition of new PBP which is resistant)
• can result in loss of efficacy or decreased potency
• eg. MRSA (S. aureus undergoes gene-transfer)

Question 3

Describe the mechanism of beta lactam resistance through the production of inactivating enzymes

Answer 3

• bacterial production of beta-lactamases - lyses the beta-lactam ring to inactivate the antibiotic
• usually causes total antibiotic failure
• eg. Gram-negative bacilli and S. aureus (common)

Question 4

How can the production of beta-lactamases be resolved?

Answer 4

• alteration of molecule = synthetic beta-lactams with structures resistant to lysis by beta-lactamases
• beta-lactamase inhibitors = molecules which inactivate beta-lactamases to prevent action on beta-lactam

Question 5

What are extended spectrum beta-lactamases?

Answer 5

• beta-latamases capable of lysing ceftriazone and similar antibiotics
• meropenem recommended for severe infections (typically given until causative organism determined)

Question 6

Describe the mechanisms of carbapenem resistance

Answer 6

• production of carbapenemases by bacteria
• reduced membrane permeability by alteration of porin in the cell wall which disallows antibiotics from gaining entry into the bacterial cell wall

Question 7

Describe the mechanisms of S. aureus resistance

Answer 7

• beta-lactamase production by bacteria (results in penicillin failure, overcame by beta-lactamase stable pencillins - flucloxacillin)
• altered PBPs (resulted in failure of flucloxacillin (MRSA), overcame by use of vancomycin which has different mechanism of action)

Question 8

Which bacterium does S. aureus acquire the resistant PBP gene from?

Answer 8

• S. fleurettii
• Mec A gene

Question 9

What are the personal risk factors for antibiotic resistance?

Answer 9

• antibiotic consumption within last 6 months
• overnight stays in hospital (exposure to antibiotic resistant bacteria)
• visiting countries with high incidence of drug resistance
• after risk acquired, can persist for months