Antimicrobials & Antimicrobial Resistance (38) - End E3

Question 1

T/F: We induce antibiotic resistant bacteria

Answer 1

FALSE - we selectively encourage growth of bacteria with mutations

Question 2

What is constitutive resistance?

Answer 2

bacteria are resistant to antibiotic because they lack the uptake system or targets of the antibiotic
- penicillin G cannot enter members of the family enterobacteriaceae

unrelated to previous antibiotic exposure

Question 3

What is acquired resistance?

Answer 3

bacteria become resistant to antibiotics by mutations, resulting in alteration of uptake systems or targets of antibiotics

dependent on prior exposure

Question 4

What are the 3 mechanisms of acquired resistance?

Answer 4

1. alter the target of the drug
2. after uptake; inhibit uptake, increase excretion
3. inactivate the drug

Question 5

Describe altering the target of the drug via mechanism of acquired resistance

Answer 5

modify the target site - methylation of rRNA by gram + bacteria induces resistance to macrolides, which normally binds ribosomal subunit

reduce significance of the target site: development of alternative pathways

Question 6

Describe step two regarding acquired resistance

Answer 6

inhibit uptake (decrease pore size)
increase excretion (tetracyclines)

Question 7

Describe mechanism of acquired resistance - step 3 of inactivating the drug

Answer 7

synthesis of inactivating enzymes

• beta-lactamases for penicillins and cephalosporins
• acetyl transferase which activates chloramphenicol to a non-binding form

Question 8

What is multi-antibiotic resistance?

Answer 8

implies multiple DIFFERENT resistance mechanisms - different classes

Question 9

What is cross-resistance regarding resistance to several antibiotics?

Answer 9

resistance due to a COMMON mechanism - so that resistance to one antibiotic implies resistance to others = same class

Question 10

Give example of cross-resistance of aminoglycosides

Answer 10

resistance to new drug (amikacin) implies resistance to older aminoglycocides (gentamicin)

Question 11

Cross-resistance is [uni/bi/multi]-directional. Why?

Answer 11

unidirectional

newer aminoglycosides have greater stability to destruction by enzymes than older

Question 12

Give cross-resistance regarding b-lactams

Answer 12

an organism could be resistant to several beta lactams (penicillin, ampicillin, cefazolin) via production of beta-lactamase

Question 13

What are two basic mechanisms by which bacteria acquire resistance?

Answer 13

1. changes in DNA via MUTATION
2. acquisition of DNA

Question 14

What is acquired resistance via mutations?

Answer 14

changes in genotype (DNA) - most frequently artist as errors during replication

Question 15

If mutations are not lethal, what happens?

Answer 15

may confer selective disadvantage will most likely be lost over time

no advantage: maintained at low level

selective advantage: increase in population until they may become dominant type

Question 16

Antibiotic resistance only confers selective advantage if ________

Answer 16

antibiotics are present (selective pressure)

Question 17

What is genetic transfer (acquisition of DNA) - acquired resistance mechanism?

Answer 17

transfer of DNA between strains of a given species, different species, or different genera

generate genetic diversity

Question 18

What are the steps of genetic transfer?

Answer 18

transformation
conjugation
transduction

Question 19

Why is genetic transfer important? It is responsible for _____

Answer 19

important in antibiotic resistance

responsible for multi-antibiotic resistance

Question 20

What is transduction regarding acquired resistance - genetic transfer

Answer 20

transfer of DNA following bacteriophage infection

• bacteriophage DNA is integrated into bacterial chromosome

Question 21

Once inside (after transduction), familiarize yourself with the steps

Answer 21

Question 22

What is conjugation regarding acquired resistance - genetic transfer

Answer 22

inter-bacterial DNA transfer through sex pilus
plasmids can encode: pili genes, exotoxins, MULTIPLE antibiotic resistance (R plasmids)

plasmids usually encode factors NOT essential for growth and replication

Question 23

Plasmids are transferred how?

Answer 23

vertically during bacterial division and horizontally during conjugation

Question 24

Where are transfer of plasmids common in?

Answer 24

gram negative

plasmids can be transferred within a bacterial species, between species, or between genera

Question 25

How do you select an antibiotic?

Answer 25

gram-related spectra
historial data
in vitro sensitivity and antibiotic sensitivity testing

Question 26

What is this?

Answer 26

disk diffusion (Kirby-bauer procedure)

Question 27

What is this?

Answer 27

an e-test

Question 28

What does susceptible mean?

Answer 28

an infection due to the isolate may be treated in body sites with the recommended dosage

Question 29

What does resistant mean?

Answer 29

resistant isolates are not inhibited by the usual achievable concentration of a drug and not reliable in treatment

Question 30

What does intermediate mean?

Answer 30

an infection due to the isolate may be treated in body sites where high dosage of drug can be used

Question 31

What does no interpretation mean?

Answer 31

there are no interpretative criteria established yet

Question 32

What are clinical considerations in prescribing antimicrobial drugs?

Answer 32

safety and side effects - toxicity, allergies
routes of administration

Question 33

Describe different effects of oral, IM, and IV

Answer 33

Question 34

What are strategies for limiting antibacterial resistance?

Answer 34

Question 35

What is this showing?

Answer 35

an example of synergism between two antimicrobial agents