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Medical & General Microbiology > Antibiotic Resistance Mechanisms > Flashcards

Antibiotic Resistance Mechanisms Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

Antimicrobial resistance is

A

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

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2
Q

Resistance is measured by

A

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

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3
Q

MIC

A

Minimum Inhibitory Concentration

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

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4
Q

MBC

A

Minimum Bacteriocidal Concentration

The lowest concentration of an antimicrobial that kills in vitro

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5
Q

A breakpoint is

A

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

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6
Q

MIC less than or equal to the breakpoint

A

Bacteria susceptible to the AB

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7
Q

MIC greater than the breakpoint

A

Bacteria resistant to the AB

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8
Q

A bacteriostatic agent

A

Reaches MIC levels in the blood/tissues

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9
Q

A bacteriocidal agent

A

Reaches CIDAL levels in the blood/tissues

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10
Q

A broad spectrum agent

A

Has low MICs for many different bacterial types

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11
Q

A narrow spectrum agent

A

Has low MICs for only a few bacterial types

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12
Q

A sensitive (susceptible) microbe

A

Is inhibited by an agent at a low MIC

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13
Q

A resistant microbe

A

Is inhibited by an agent only at high MIC

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14
Q

Neisseria Gonhorrheae

A

Resistant to 3rd generation cephalosporins

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15
Q

Drug inactivation

A
  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
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16
Q

3rd generation cephalosporins

A

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

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17
Q

Beta lactamase genes

A

Are found mostly on plasmids

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18
Q

Staph aureus is resistant to penicillin because

A

Of the presence of a penicillinase

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19
Q

Transpeptidase is also called

A

A penicillin binding protein (inhibited by penicillin)

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20
Q

S. aureus is resistant to methicillin because

A

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

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21
Q

MecA is

A

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

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22
Q

Staph cassette chromosome mec elements are

A

Mobile genetic elements

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23
Q

PBP

A

Penicillin binding protein

24
Q

Aminoglycosides

A

Protein synthesis inhibitors
Target 30S subunit
Produced by Streptomyces

25
Q

Phosphotransferase stops streptomyces killing itself

A

Encoded by streptomyces phosphorylates OH group so the streptomycin is inactivated

26
Q

Mutations in the gene encoding the ribosomal protein S12

A

is another resistance mechanism in Streptomycin resistance

27
Q

Chloramphenicol is a

A

Synthetic AB

28
Q

Chloramphenicol targets the

A

50S subunit

Protein synthesis inhibitor

29
Q

Chloramphenicol is inactivated by

A

Acetylation of two hydroxyl groups

30
Q

The enzyme that modifies chloramphenicol is called

A

Chloramphenicolacetyltransferase

31
Q

Chromosomally encoded cmlA

A

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

32
Q

OmpA

A

Outer membrane porin

33
Q

Mutations in the 50S subunit genes

A

Are rare

34
Q

Drug efflux pumps are present in

A

All Gram negative and Positive bacteria except RND family

35
Q

TolC is an

A

Outer membrane transporter protein found in Gram negative bacteria

36
Q

In E coli Acr-AB-TolC can extrude

A

Chloramphenicol, Fluoroquinolone, Tetracycline, Novobiocin and beta lactams

37
Q

AcrA is a

A

Membrane fusion protein

38
Q

AcrAB-TolC is a

A

Efflux Tripartite system in gram negatives

39
Q

Many efflux systems can pair up with

A

AcrAB

40
Q

The main mediator of resistance to tetracyclines are

A

Drug efflux pumps

41
Q

Tetracyclines target the

A

30S subunit

Protein synthesis inhibitor

42
Q

Drug efflux genes for tetracyclines are normally based on

A

Plasmids

43
Q

R plasmids can be up to a

A

100Kb

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

44
Q

R plasmids can encode for

A

More than one resistance mechanism

45
Q

Transposons are

A

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

46
Q

Transposons often contain

A

Antibiotic resistance genes

47
Q

Resistance genes can be transferred by

A

Vertical OR Horizontal gene transfer

48
Q

Antibiotics provide

A

Selection pressure

Consequence is evolution and spread of resistance genes

49
Q

The main cause of the spread of AB resistance is

A

Horizontal gene transfer

50
Q

Horizontal gene transfer is

A

Rapid, spreads between cells without needing the presence of antibiotic

51
Q

Three mechanisms of horizontal gene transfer

A
  1. Transformation
  2. Transduction
  3. Conjugation
52
Q

Competent bacteria

A

Take up DNA naturally

53
Q

Transformation is

A

Uptake of foreign DNA

54
Q

Transduction is

A

Using phage to transfer genetic material from one bacterium to another

55
Q

Conjugation is

A

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

56
Q

Transformation is mediated by

A

Competence proteins

57
Q

Competence proteins

A

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

Medical & General Microbiology (24 decks)

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