Antimicrobial Chemotherapy 2

Question 1

Define the clinical definition of bacterial resistance.

Answer 1

Bacteria are considered resistant when it is unlikely to respond to attainable levels of that drug in tissues.

Question 2

Define the zone of inhibition.

Answer 2

Where the bacteria cannot grow.

Question 3

Describe inherent bacterial resistance.

Answer 3

Resistance of a bacterium without the need for mutations or gain of further genes.

Question 4

Describe intrinsic bacterial resistance.

Answer 4

Intrinsic resistance is characterised by the continued improvement of resistant mechanisms via cell wall and other features.

Question 5

Describe the clinically significant resistance mechanism of Beta-lactamases.

Answer 5

Beta-lactamase is a bacterial enzyme that cleaves the Beta-Lactam ring off of an antibiotic, rendering it inactive.

Question 6

Describe the clinically significant resistance mechanism of MRSA’s.

Answer 6

MRSA’s are methicillin resistant staphylococcus aureus.
This bacteria has developed resistance to B-lactams by changing the structure of their PBPs.
This means that their binding site is altered meaning the B-lactam can no longer bind.

Question 7

Name the drugs used in the treatment of MRSA.

Answer 7

MRSA is untreatable by penicillin.
Treated with Flucloxacillin and Vancomycin.

Question 8

Describe the ways in which drugs can combat B-lactamase in bacteria.

Answer 8

The antibiotic side chain can be modified, producing new antibiotic resistant to the action of B-Lactamase = co-amoxiclav.
Another method is to introduce a second component to the antibiotic (B-Lactamase inhibitor) protecting the B-lactam ring. = flucloxacillin.

Question 9

Name the main known antibacterial that Streptococci is resistant to.

Answer 9

Streptococci is always resistant to aminoglycosides.

Question 10

Name the main known antibacterial that all gram negative organisms are resistant to.

Answer 10

Gram negative organisms are always resistant to Vancomycin.
(due to its inability to penetrate the bacterial cell wall)

Question 11

Describe spontaneous mutation as a way of acquiring resistance

Answer 11

Spontaneous mutation is a change in structure or function, which no longer allows the antibiotic to act (e.g. target may have changed).

Question 12

Describe spread of resistance as a way of acquiring mutation.

Answer 12

Genes that code for resistance can pass between organisms through horizontal gene transfer, carried on plasmids or transposons.

Question 13

Define “conjugtion”

Answer 13

Conjugation is where DNA transfer bacterial cells (most common).

Question 14

Define “transformation”

Answer 14

This is the naked uptake of DNA.

Question 15

Define “transduction”

Answer 15

This is where bacterial DNA is transferred by viruses (phage).

Question 16

Describe the clinical importance of the resistance of gram negative organisms to carbapenems.

Answer 16

Carbapenems are members of the Beta-Lactam class.
Over time, gram negative bacteria have began developed Carbapenemase-producing Enterobacteriaceae (CPE).
These are members of the Enterobacteriaceae family, resistant to the carbapenem class of antibiotics (broad) through production of carbapenemase.
CPE are now endemic in health.

Question 17

Describe the mechanism of Glycopeptide resistance (vancomycin).

Answer 17

Resistance (among gram positive organisms) is acquired through conjugation or transformation.
Vancomycin resistant enterococci have emerged.
In VRE the peptidoglycan precursor to which vancomycin normally binds has an altered structure.