Mechanisms of Antibiotic Resistance Flashcards

1
Q

Penicillin cannot pass through the _______, so all Gram-negative bacteria are resistant to penicillins.

A

porin channels

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2
Q

Efflux pumps can be found in _______ or _______.

A

Gram-positive; Gram-negative

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3
Q

Efflux pumps can be ____________.

A

specific (such as the pump for tetracycline) or general

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4
Q

How do beta-lactams work?

A

They irreversibly bind to penicillin-binding proteins; PBPs are the two enzymes that are responsible for stage 3 cell-wall synthesis, transpeptidase and transglycosylase.

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5
Q

There are three ways that bacteria become resistant to beta-lactams: _________.

A

they alter their PBPs, decrease entry through porins, or degrade the drug

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6
Q

Genes for beta-lactamases are found ___________.

A

in chromosomes and plasmids; in Gram-positive and Gram-negative bacteria

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7
Q

Most beta-lactamases can be inhibited by _____________.

A

beta-lactamase inhibitors

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8
Q

List the characteristics of penicillinases.

A

They (1) only break down penicillins; (2) are not active against cephalosporins; (3) can be located in chromosomes or on transferable elements; and (4) are susceptible to beta-lactamase inhibitors.

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9
Q

All Staphylococcus are resistant to ___________ because of the ________ gene.

A

penicillin, amoxicillin, and ampicillin; bla

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10
Q

E. coli occasionally becomes resistant to ________ with its TEM-1 plasmid.

A

ampicillin

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11
Q

K. pneumoniae is resistant to ampicillin because of a __________ gene.

A

chromosomal (SHV-1)

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12
Q

MSSAs have bla, so they will not be killed by _________, but they can be killed by drugs that are not susceptible to beta-lactamases.

A

penicillin, amoxicillin, or ampicillin

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13
Q

ESBLs are ____________.

A

extended-spectrum beta-lactamases, enzymes that can degrade penicillins and cephalosporins

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14
Q

ESBLs are transmitted __________.

A

on plasmids

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15
Q

ESBLs are still sensitive to __________.

A

some beta-lactamase inhibitors

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16
Q

ESBL-possessing bacteria can be killed with _______.

A

carbapenems

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17
Q

ampC is located in _________.

A

chromosomes of Gram-negative rods

18
Q

Where is ampC found? What are some of its characteristics?

A

In Gram-negative rods (Pseudomonas and Enterobacter, to be specific); it can degrade penicillins and cephalosporins; it is not susceptible to beta-lactamase inhibitors, but the bacteria remain susceptible to carbapenems; is inducible

19
Q

The production of ampC is induced by _________.

A

ampicillin and cefazolin; it can be constitutively activated by a random mutation

20
Q

Carbapenemases degrade ___________.

A

penicillins, cephalosporins, and carbapenems (i.e., all beta-lactams)

21
Q

Carbapenemases are not ___________.

A

susceptible to beta-lactamase inhibitors

22
Q

Carbapenems are found on ___________.

A

plasmids (frequently taken up by E. coli and Klebsiella)

23
Q

The two carbapenemases known are _________.

A

KPC and NDM-1

24
Q

Staphylococcus aureus becomes MRSA when it acquires __________.

A

a plasmid encoding mecA (PBP2a), a penicillin-binding protein

25
Q

Because it is a unique PBP, mecA causes S. aureus to be resistant to ___________.

A

all beta-lactams

26
Q

Similar to MRSA, Streptococcus pneumoniae and Neisseria gonorrhoeae become resistant to penicllins by ________.

A

altering its PBP, creating a new target

27
Q

Streptococcus have never been shown to ___________.

A

express beta-lactamases–they are all resistant by altering PBP structure

28
Q

What does vancomycin bind to?

A

D-alanine dimers on the end of the peptide that hangs off of MurNAc; it is so big, comparatively, that it prevents peptidoglycan from cross-linking

29
Q

There are only two drugs that treat Clostridium difficile: ___________.

A

metronidazole and vancomycin

30
Q

How does Enterococcus become resistant to vancomycin?

A

It gets a plasmid that expresses an enzyme that converts D-alanine D-alanine to D-alanine D-lactate

31
Q

By what two ways do bacteria become resistant to macrolides?

A

Through the msr gene (which pumps out macrolides) and the erm gene (which modifies the 23S subunit of the 50S subunit of bacterial rRNA

32
Q

erm (methylation of the 50S subunit) is inducible or constitutive; when it is induced by macrolides or constitutively turned on, however, it leads to resistance to ________, as well.

A

clindamycin

33
Q

If a D-test is positive, this indicates that the Staph is erm (_______); do not administer clindamycin, because you might _________.

A

inducible; select for mutants that are constitutive erm

34
Q

The majority of fluoroquinolone resistance occurs by ____________.

A

point mutations (in the quinolone-resistance determining region “QRDR”)

35
Q

Almost all resistance to aminoglycosides occurs by ______________.

A

drug modification

36
Q

Vancomycin cannot pass through ____________.

A

the outer membrane of Gram-negative organisms

37
Q

There are three narrow beta-lactamases. Which two are plasmid-mediated?

A

bla and TEM-1 (SHV is chromosomal)

38
Q

How has MRSA become resistant?

A

It acquired mecA, a PBP2a gene that cannot be targeted by any beta-lactam except cefepime and ceftaroline

39
Q

How is vancomycin resistance carried?

A

On plasmids encoding vanA and vanB

40
Q

Most E. coli and Klebsiella contain ______, which is why they’re not susceptible to _________.

A

a narrow-spectrum beta-lactamase; penicillin