Antibiotic Resistance Mechanisms

Question 1

Antimicrobial resistance is

Answer 1

Resistance of a microbe to a drug that was originally effective for treatment of infections caused by it

Question 2

Resistance is measured by

Answer 2

The increase in the Minimum Inhibitory Concentration of a drug (MIC)

Question 3

MIC

Answer 3

Minimum Inhibitory Concentration

The lowest concentration of an antimicrobial drug that will inhibit visible growth after overnight incubation

Question 4

MBC

Answer 4

Minimum Bacteriocidal Concentration

The lowest concentration of an antimicrobial that kills in vitro

Question 5

A breakpoint is

Answer 5

A chosen concentration of an antibiotic that defines whether a species is susceptible or resistant to an antibiotic

Question 6

MIC less than or equal to the breakpoint

Answer 6

Bacteria susceptible to the AB

Question 7

MIC greater than the breakpoint

Answer 7

Bacteria resistant to the AB

Question 8

A bacteriostatic agent

Answer 8

Reaches MIC levels in the blood/tissues

Question 9

A bacteriocidal agent

Answer 9

Reaches CIDAL levels in the blood/tissues

Question 10

A broad spectrum agent

Answer 10

Has low MICs for many different bacterial types

Question 11

A narrow spectrum agent

Answer 11

Has low MICs for only a few bacterial types

Question 12

A sensitive (susceptible) microbe

Answer 12

Is inhibited by an agent at a low MIC

Question 13

A resistant microbe

Answer 13

Is inhibited by an agent only at high MIC

Question 14

Neisseria Gonhorrheae

Answer 14

Resistant to 3rd generation cephalosporins

Question 15

Drug inactivation

Answer 15

1. Enzymes that modify the drug
   e. g. chloramphenicol acetyl transferase
2. Enzymes that inactivate the drug
   e. g. beta lactamases break down the lactam ring
3. Alteration of drug target site
   e. g. ribosomal mutation stops streptomycin binding
4. Drug efflux pumps
5. Modification of membrane permeability

Question 16

3rd generation cephalosporins

Answer 16

Modify the R groups of the beta lactam ring to increase permeability to interrupt peptidoglycan biosynthesis

Question 17

Beta lactamase genes

Answer 17

Are found mostly on plasmids

Question 18

Staph aureus is resistant to penicillin because

Answer 18

Of the presence of a penicillinase

Question 19

Transpeptidase is also called

Answer 19

A penicillin binding protein (inhibited by penicillin)

Question 20

S. aureus is resistant to methicillin because

Answer 20

It has a penicillin binding protein encoded by mecA with a lower binding affinity for the beta lactams

Question 21

MecA is

Answer 21

A variant penicillin binding protein in S. aureus with a lower affinity for beta lactams, resulting in resistance to virtually all beta lactam antibiotics

Question 22

Staph cassette chromosome mec elements are

Answer 22

Mobile genetic elements

Question 23

PBP

Answer 23

Penicillin binding protein

Question 24

Aminoglycosides

Answer 24

Protein synthesis inhibitors
Target 30S subunit
Produced by Streptomyces

Question 25

Phosphotransferase stops streptomyces killing itself

Answer 25

Encoded by streptomyces phosphorylates OH group so the streptomycin is inactivated

Question 26

Mutations in the gene encoding the ribosomal protein S12

Answer 26

is another resistance mechanism in Streptomycin resistance

Question 27

Chloramphenicol is a

Answer 27

Synthetic AB

Question 28

Chloramphenicol targets the

Answer 28

50S subunit | Protein synthesis inhibitor

Question 29

Chloramphenicol is inactivated by

Answer 29

Acetylation of two hydroxyl groups

Question 30

The enzyme that modifies chloramphenicol is called

Answer 30

Chloramphenicolacetyltransferase

Question 31

Chromosomally encoded cmlA

Answer 31

A gene that causes resistance to choramphenicol by producing more OmpA that leads to reduced membrane permeability

Question 32

OmpA

Answer 32

Outer membrane porin

Question 33

Mutations in the 50S subunit genes

Answer 33

Are rare

Question 34

Drug efflux pumps are present in

Answer 34

All Gram negative and Positive bacteria except RND family

Question 35

TolC is an

Answer 35

Outer membrane transporter protein found in Gram negative bacteria

Question 36

In E coli Acr-AB-TolC can extrude

Answer 36

Chloramphenicol, Fluoroquinolone, Tetracycline, Novobiocin and beta lactams

Question 37

AcrA is a

Answer 37

Membrane fusion protein

Question 38

AcrAB-TolC is a

Answer 38

Efflux Tripartite system in gram negatives

Question 39

Many efflux systems can pair up with

Answer 39

AcrAB

Question 40

The main mediator of resistance to tetracyclines are

Answer 40

Drug efflux pumps

Question 41

Tetracyclines target the

Answer 41

30S subunit | Protein synthesis inhibitor

Question 42

Drug efflux genes for tetracyclines are normally based on

Answer 42

Plasmids

Question 43

R plasmids can be up to a

Answer 43

100Kb | so can have up to 100 genes on them - quite a lot

Question 44

R plasmids can encode for

Answer 44

More than one resistance mechanism

Question 45

Transposons are

Answer 45

'Jumping genes' Mobile genetic elements that jump in and out of chromosomes Can also be found on plasmids

Question 46

Transposons often contain

Answer 46

Antibiotic resistance genes

Question 47

Resistance genes can be transferred by

Answer 47

Vertical OR Horizontal gene transfer

Question 48

Antibiotics provide

Answer 48

Selection pressure | Consequence is evolution and spread of resistance genes

Question 49

The main cause of the spread of AB resistance is

Answer 49

Horizontal gene transfer

Question 50

Horizontal gene transfer is

Answer 50

Rapid, spreads between cells without needing the presence of antibiotic

Question 51

Three mechanisms of horizontal gene transfer

Answer 51

1. Transformation 2. Transduction 3. Conjugation

Question 52

Competent bacteria

Answer 52

Take up DNA naturally

Question 53

Transformation is

Answer 53

Uptake of foreign DNA

Question 54

Transduction is

Answer 54

Using phage to transfer genetic material from one bacterium to another

Question 55

Conjugation is

Answer 55

Transfer of a plasmid through an F pilus. The donor bacterium needs a DNA sequence called the fertility factor, or F-factor.

Question 56

Transformation is mediated by

Answer 56

Competence proteins

Question 57

Competence proteins

Answer 57

Pull in and unwind DNA Same proteins that are involved in Type 4 secretion systems Found in G+ and G- bacteria