Antibiotic Resistance

Question 1

Define resistance?

Answer 1

When a previously susceptible organism is no longer inhibited by an antibiotic at levels that can be safely achieved clinically.

Question 2

What is intermediate resistance?

Answer 2

Can be treated with an increase from the standard dose.

Question 3

What is the theraputic index

Answer 3

The difference between dose necessary for treatment and that causing harm, this is usually large.

Question 4

What is a minimum inhibitory concentration?

Answer 4

The lowest concentration of an antibiotic that completely inhibits the growth of a bacterium

Question 5

What is the minimum bactericidal concentration?

Answer 5

The lowest dose that completely kills a bacterium

Question 6

What is the antibiotic breakpoint?

Answer 6

A concentration chosen for laboratory testing that will differentiate sensitive from resistant populations of bacteria. This allows laboratories to test only one concentration rather than having to determine the MIC.

Question 7

What defines the breakpoint?

Answer 7

• Distribution of MICs of target bacteria,
• Achievable theraputic concentration in tissue
• Maximum achievable concentration

Question 8

Describe how streptococci are naturally resistant to an antibiotic class and what class is this?

Answer 8

Aminoglycosides. This occurs because the MIC is above a concentration that would cause toxicity

Question 9

What are pseudomonas species resistant to and what is this mechanism?

Answer 9

Resistant to beta lactams. This is because intrinsic beta lactamases can be overcome by design

Question 10

What are mycoplasma species resistant too? what is the mechanism

Answer 10

Beta-lactam antibiotics which is because the cell wall has no peptidoglycan

Question 11

What are enterobacteriaciae resistant too? What is the mechanism?

Answer 11

Metronidazole because they grow in aerobic conditions

Question 12

What is acquired resistance?

Answer 12

It occurs when a previously susceptible strain or species develops an increase in the MIC that takes in beyond the theraputic range.

Question 13

Name examples of antibiotics that are inactivated by destruction?

Answer 13

Cephalosporins, expanded spectrum beta-lactamases

Question 14

What antibiotics are inactivated by addition?

Answer 14

Aminoglycosides

Question 15

What are examples of antibiotics that are inactivated by efflux?

Answer 15

Tetracyclines, quinolones and macrolides. This may be involved in organisms gaining higher levels of resistance

Question 16

Describe the mechanism of resistance of methicillin resistance of S.aureus?

Answer 16

They have an alternative pathway that is not targeted.

Question 17

Describe the evolution of quinolone resistance?

Answer 17

There are two genes involved - gyrA and parC. They are point mutations in the genes affinity of the proteins for DNA.
Mutation in one gene encodes low level resistance, in both genes encodes high level resistance.

Question 18

What is transformation?

Answer 18

Where bacteria picks up free DNA giving it an altered gene

Question 19

What is conjugation?

Answer 19

Exchange of plasmids between two bacterium. These encode for virulence, metabolic function and resistance determinants. This allows for characteristics to be shared rapidly by bacteria.

Question 20

Describe features of transposons and integrons

Answer 20

They are small sections of DNA that encode their own transmission. They may collect resistance determinants. Instead of sharing whole plasmid, bacteria can share a small part of DNA (transposon)

Question 21

What is a superbug?

Answer 21

An organism that has gained resistance to a critical antibiotic or multiple antibiotics

Question 22

Name some examples of superbugs

Answer 22

• Methicilin resistant staph aureus (MRSA)
• Glycopeptide resistant staph aureus (GRSA)
• Vancomycin resistant enterococcus

Question 23

Name some groups of carbapenemases

Answer 23

Klebsiella pneumoniae carbapenemase (KPS), New Delhi metallo betalactamse (NDM) and Oxa-48 group

Question 24

What makes us more worried about certain resistant bacteria?

Answer 24

• When the consequences of infection are severe and the organism is common.
• When the organism is naturally resistant.
• When the infection site is where it is difficult to get high concentrations of antibiotic (meningitis)

Question 25

How can we address the problem of antibiotic resistance?

Answer 25

• Optimise treatment of bacterial disease,
• Better diagnostics,
• Focused treatment,
• Appropriate length of courses

Question 26

How do we treat resistant bugs?

Answer 26

• Culture,
• Susceptibility testing,
• Use of most bactericidal drug available,
• Consider use of combinations.