Mechanisms of Antibiotic Resistance Flashcards Preview

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Flashcards in Mechanisms of Antibiotic Resistance Deck (40):
1

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

porin channels

2

Efflux pumps can be found in _______ or _______.

Gram-positive; Gram-negative

3

Efflux pumps can be ____________.

specific (such as the pump for tetracycline) or general

4

How do beta-lactams work?

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

5

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

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

6

Genes for beta-lactamases are found ___________.

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

7

Most beta-lactamases can be inhibited by _____________.

beta-lactamase inhibitors

8

List the characteristics of penicillinases.

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.

9

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

penicillin, amoxicillin, and ampicillin; bla

10

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

ampicillin

11

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

chromosomal (SHV-1)

12

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

penicillin, amoxicillin, or ampicillin

13

ESBLs are ____________.

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

14

ESBLs are transmitted __________.

on plasmids

15

ESBLs are still sensitive to __________.

some beta-lactamase inhibitors

16

ESBL-possessing bacteria can be killed with _______.

carbapenems

17

ampC is located in _________.

chromosomes of Gram-negative rods

18

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

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

The production of ampC is induced by _________.

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

20

Carbapenemases degrade ___________.

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

21

Carbapenemases are not ___________.

susceptible to beta-lactamase inhibitors

22

Carbapenems are found on ___________.

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

23

The two carbapenemases known are _________.

KPC and NDM-1

24

Staphylococcus aureus becomes MRSA when it acquires __________.

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

25

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

all beta-lactams

26

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

altering its PBP, creating a new target

27

Streptococcus have never been shown to ___________.

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

28

What does vancomycin bind to?

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

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

metronidazole and vancomycin

30

How does Enterococcus become resistant to vancomycin?

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

31

By what two ways do bacteria become resistant to macrolides?

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

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.

clindamycin

33

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

inducible; select for mutants that are constitutive erm

34

The majority of fluoroquinolone resistance occurs by ____________.

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

35

Almost all resistance to aminoglycosides occurs by ______________.

drug modification

36

Vancomycin cannot pass through ____________.

the outer membrane of Gram-negative organisms

37

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

bla and TEM-1 (SHV is chromosomal)

38

How has MRSA become resistant?

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

39

How is vancomycin resistance carried?

On plasmids encoding vanA and vanB

40

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

a narrow-spectrum beta-lactamase; penicillin

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