Mechanisms of Antibiotic Resistance Flashcards

1
Q

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

A

porin channels

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Efflux pumps can be found in _______ or _______.

A

Gram-positive; Gram-negative

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Efflux pumps can be ____________.

A

specific (such as the pump for tetracycline) or general

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Genes for beta-lactamases are found ___________.

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Most beta-lactamases can be inhibited by _____________.

A

beta-lactamase inhibitors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

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

A

penicillin, amoxicillin, and ampicillin; bla

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

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

A

ampicillin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

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

A

chromosomal (SHV-1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

ESBLs are ____________.

A

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

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

ESBLs are transmitted __________.

A

on plasmids

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

ESBLs are still sensitive to __________.

A

some beta-lactamase inhibitors

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

ESBL-possessing bacteria can be killed with _______.

A

carbapenems

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
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
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