Antibiotic Resistance Mechanisms

Question 1

What term describes antibiotic resistance that exists because of a bacterium’s inherent structural or functional characteristics?

Answer 1

Intrinsic or Natural Resistance

Question 2

What term describes antibiotic resistance that arises due to spontaneous chromosomal changes?

Answer 2

Mutational resistance

Question 3

What term describes antibiotic resistance that a bacterium gains through the transfer of genetic material?

Answer 3

Acquired resistance

Question 4

List 3 mechanisms by which horizontal gene transfer occurs.

Answer 4

Transformation, transduction, and conjugation

Question 5

Which of the following factors INCREASES antibiotic resistance mutation rates: high antibiotic concentrations, long antibiotic exposure time, large variety of R genes, and bacteria starvation?

Answer 5

Large variety of R genes and bacteria starvation/stress increase mutation rates (the other two choices would decrease antibiotic resistance)

Question 6

What is the term for an autonomously replicating genetic element consisting of closed, circular, double-stranded DNA?

Answer 6

Plasmid

Question 7

What is the term for a transposable genetic element that cannot replicate autonomously, and which codes for functional genes?

Answer 7

Transposon

Question 8

What is the term for a transposable genetic element that cannot replicate autonomously, and which encodes only genes involved in insertion events (such as promoters)?

Answer 8

Insertion sequence

Question 9

What is the term for a recombinant “hot spot” near a promoter site where mobile gene cassettes can insert their antibiotic-resistance genes?

Answer 9

Integron

Question 10

What happens to the level of expression of a resistance gene as the distance between a promoter and an integron-related gene cassette increases?

Answer 10

The amount of expression goes down

Question 11

Which of the following are NOT mechanisms of antibiotic resistance: enzyme inactivation, decreased permeability, decreased efflux, alteration of target site, protection of target site, decreased production of target, bypass of inhibited process, increased antibiotic binding

Answer 11

Decreased efflux and decreased target production would increase rather than decrease antibiotic susceptibility

Question 12

The most important form of antibiotic resistance involves bacterial inactivation of the antibiotic enzyme. What class of antibiotics is targeted by this inactivation, and what does the bacteria protect as a result?

Answer 12

Beta-lactams are inactivated, thereby allowing bacterial cell wall synthesis

Question 13

What kind of beta-lactamase confers only resistance to penicillin and narrow-spectrum cephalosporins?

Answer 13

Narrow-spectrum beta-lactamase (NSBL)

Question 14

What kind of beta-lactamase confers resistance to penicillin, third generation cephalosporins, and monobactams, but remain susceptible to cephamycins and carbapenems?

Answer 14

Extended-spectrum beta-lactamase (ESBL)

Question 15

What antibiotics are the most effective for treating ESBL-producing Enterobacteriaceae?

Answer 15

Carbapenems

Question 16

Clavulanic acid, sulbactam, and tazobactam are what kind of drug, and what class of antibiotic-resistant bacteria are they useful against?

Answer 16

Beta-lactamase inhibitors; used for ESBL bacteria (AmpC beta-lactamase and carbapenems are not susceptible to beta-lactamase inhibitors)

Question 17

What kind of beta-lactamase confers resistance to penicillin, most cephalosporins, and cephamycins, but remains susceptible to fourth generation cephalosporins and to carbepenems?

Answer 17

Amp C beta-lactamase

Question 18

What kind of beta-lactamase is usually a chromosomal, inducible enzyme found on Enterobacteria and is resistant to beta-lactamase inhibitors like sulbactam and tazobactam?

Answer 18

Amp C beta-lactamase (they are primarily chromosomal, but plasmid-mediated versions have also been observed)

Question 19

List the 4 categories of Gram(-) beta-lactamases, as classified by their level of resistance.

Answer 19

Narrow spectrum (NSBL), Extended-spectrum (ESBL), Amp C, and Carbapenemases

Question 20

List 5 groups of antibiotics which carbapenemases are resistant to.

Answer 20

Penicillins, cephalosporins, monobactams, cephamycins, and carbapenems

Question 21

The ESBL (extended-spectrum beta-lactamases) are primarily associated with what 3 bacteria?

Answer 21

Klebsiella, E. coli, and Proteus

Question 22

KPC and CRE bacteria are associated with what level of antibiotic resistance enzymes?

Answer 22

With carbapenemases - KPC is Klebsiella pneumonia carbapenemase and CRE is carbapenem-resistant enterobacteria

Question 23

In bacteria carrying chromosomal AmpC beta-lactamases, about how many days does it take for beta-lactamase expression to be induced?

Answer 23

20-30 days

Question 24

Penicillinase-resistant penicillin is used primarily to treat what two kinds of penicillinase producing bacteria?

Answer 24

Staph aureus (other than MRSA) and Staph epidermidis

Question 25

Methicillin, oxacillin, cloxacillin, dicloxacillin, and nafcillin all share what common feature not found in penicillin G?

Answer 25

They are all resistant to penicillinase

Question 26

In MRSA, what is the mechanism of methicillin resistance: enzyme inactivation, alteration of target site, protection of target site, or increased antibiotic binding?

Answer 26

Alteration of the target site (the target being PBP)

Question 27

For Staphylococci in general, what are the 2 main mechanisms for antibiotic resistance: enzyme inactivation, alteration of target site, protection of target site, or increased antibiotic binding?

Answer 27

Enzyme inactivation (via beta-lactamases) and alteration of the target site (via mecA / PBP2a)

Question 28

Name the gene that confers methicillin resistance to MRSA, the gene cassette that it is inserted into, and the bacterial species where this cassette originated

Answer 28

mecA gene, SCCmec cassette, from coagulase(-) Staph species

Question 29

State the abnormal gene product that is made by mecA, and why this enzyme make MRSA resistant to methicillin, nafcillin, oxacillin, and cephalosporins.

Answer 29

PBP2a (penicillin-binding protein 2a); which has low affinity for antibiotics because of structural changes in the PBP enzyme

Question 30

In VRE (vancomycin-resistant enterococci), what is the mechanism of resistance: enzyme inactivation, alteration of target site, protection of target site, or increased antibiotic binding?

Answer 30

Alteration of the target site (the target being d-ala-d-ala residues where vancomycin or PBP binds)

Question 31

In VISA (vancomycin-intermediate Staph aureus), what is the mechanism of resistance: enzyme inactivation, alteration of target site, protection of target site, or increased antibiotic binding?

Answer 31

Increased antibiotic binding: the VISA cell walls trap vancomycin at the cell periphery, so that it cannot access its usual d-ala-d-ala target

Question 32

All Enterococci have intrinsic resistance to what 2 antibiotics, and why?

Answer 32

Aminoglycosides - naturally low uptake; beta-lactams - naturally low binding affinity

Question 33

Decreased permeability of bacterial membranes, which plays a role in aminoglycoside and carbapenem resistances, can result from the alteration or loss of what molecule in the bacterial outer membrane?

Answer 33

Loss of porins can lead to decreased aminoglysocide and carbapenem permeability

Question 34

What is the major mechanism of tetracycline resistance in Gram(-) enteric organisms?

Answer 34

Increased/active efflux of drug

Question 35

Overproduction of PABA, DHPS (dihydropteroate synthetase), and DHFR (dihydrofolate reductase) is associated with bacterial resistance to what antibiotics?

Answer 35

Sulfonamide (PABA and DHPS) and Trimethoprim (DHFR)

Question 36

Alterations in DNA gyrase and topoisomerase IV can lead to bacterial resistance of what antibiotics?

Answer 36

Fluoroquinolones