Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Bacteriology > Lecture 17 - Antimicrobials III > Flashcards

Lecture 17 - Antimicrobials III Flashcards

1
Q

Antimicrobials that bind to 30s ribosomal subunit

A

Aminogycosides, tetracyclines

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

Antimicrobials that target 50s ribosomal subunit

A

Chloramphenicol, macrolides

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

What does chloramphenicol target?

A

Peptidyl transfer

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

What do macrolides target?

A

Translocation

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

What does mupirocin target?

A

Isoleucyl tRNA synthesis

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

What do oxazolidones target?

A

Formation of initiation complex

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

What was the first aminoglycoside?

A

Streptomycin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is tobramycin good for?

A

Treating pseudomonas

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

What is gentamicin good for?

A

A general-purpose anti-G- antimicrobial

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

Why do aminoglycosides need to be injected?

A

Not absorbed through epithelium, so if ingested would only be active in the GIT

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

How are aminoglycosides administered?

A

injected

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Are aminoglycosides bacteriostatic or bactericidal?

A

Bactericidal

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

Stages of aminoglycodside bactericidal action
1)
2)

A

1) Binds 30s subunit, makes recognition of mRNA codons defective. Abnormal proteins form.
2) Abnormal proteins cause membrane to become more permeable. More aminoglycosides enter bacterium, cause complete ribosomal blockade

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

Why does a small amount of aminoglycoside initially enter a bacterium?

A

Aminoglycosides are lipid-insoluble.

Have difficulty passing through cell membrane, cell wall

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

What is a benefit of amikacin?

A

Resistant to a lot of enzymes which modify aminoglycosides, so as to inactivate them

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

Three types of bacteria, with respect to growth under streptomycin

A

1) StrS - Susceptible
2) StrR - Resistant
3) StrD - Dependent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Why are StrD bacteria dependent on aminoglycoside presence?

A

Ribosomes are defective. Aminoglycosides correct this defect.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Ways that aminoglycosides are modified by bacteria
1)
2)
3)

A

1) Phosphorylation
2) Adenylation
3) Acetylation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q 
Methods of microbial resistance to aminoglycosides
1)
2)
3)
4)
A

1) Efflux
2) Modified outer membrane leading to reduced entry
3) Enzymatic modification of aminoglycoside, leading to reduced entry
4) Modified 30s subunit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Example of resistance by drug inactivation
1)
2)

A

1) Beta lactams by beta lactamases (hydrolysis)

2) Covalent modification - aminoglycosides, chloramphenicol

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Example of resistance by altering target of drug
1)
2)

A

1) Modify target to a less-sensitive form - Beta-lactams, vancomycin
2) Overproduce target - Vancomycin

22
Q

Example of resistance by reducing drug access to target
1)
2)

A

1) Reduced entry into a cell - Aminoglycosides

2) Increased efflux from a cell - Aminoglycosides, tetracycline

23
Q

Example of resistance by failing to activate drug precursor
1)
2)

A

1) Metronidazole

2) Isoniazid

24
Q

How is metronidazole activated?

A

Is reduced in hydrogenosome

25
Q

What is metronidazole effective aginst?

A

Obligate anaerobes

26
Q

Examples of organisms susceptible to metronidazole

A

Giardia, entamoeba, trachomatis

27
Q

Bacteria resistant to carbapenems

A

Enterobacteriaceae

28
Q

Examples of innate resistance
1)
2)
3)

A

1) Mycoplasma - lack cell wall
2) Cell wall impenetrability (G- resistant to vancomycin)
3) Pseudomonas - beta-lactam resistance gene on chromosome

29
Q

Two cycles of phage infection

A

1) Temperate cycle - gene integrates into genome, cell isn’t lysed
2) Lytic cycle

30
Q

Example of bacterium with temperate cycle bacteriophage DNA

A

Vibrio cholerae, with choleratoxin gene from a phage

31
Q

Difference in ability to share genetic information between conjugation and transformation

A

Transformation requires that bacteria are closely-related

Conjugation can occur between unrelated bacteria (even between G+ and G- bacteria)

32
Q

Most important type of bacterial horizontal transfer

A

Plasmid-mediated

33
Q

Ways to test bacterial antimicrobial resistance
1)
2)

A

1) Dilution tests

2) Diffusion tests

34
Q

What do minimum inhibitory concentration tests test?

A

Bacteriostatic action

35
Q

How do you test bactericidal action from a MIC test?

A

Take samples from inhibited samples, culture them on a gel without antimicrobials. See which grow.
This gives MBC (minimum bactericidal concentration)

36
Q

MIC test
1)
2)

A

1) Doubling dilutions of antimicrobial of interest

2) Add bacteria of interest, see which grow, which are inhibited

37
Q

Potential problems with dilution tests
1)
2)

A

1) Takes up space. If have to test many samples, can quickly run out of room in lab
2) Patient samples often contain several bacterial species

38
Q

Solution to issues with dilution tests

A

Use diffusion tests

Disc susceptibility test

39
Q

Advantages of disc susceptibility test

A

Can test several different antimicrobials at once (each on a different disc), on the one plate

40
Q

Drawbacks of disc susceptibility test

A

Can’t directly compare diameters of inhibition, as different antimicrobials have different rates of diffusion

41
Q

Two types of antibiotic susceptibility data

A

1) Two distinct populations on graph - Beta-lactamase

2) Continuous gradient of susceptibility - Altered penicillin-binding proteins

42
Q

Break-points for pneumococci

A

Fully-susceptible MIC 1mg/L

43
Q

How to determine disc susceptibility breakpoints

A 
Chart MIC (from dilution test) for different bacteria on a graph
On same axes, for the same bacteria, chart disc susceptibility test zone diameter.

Negative correlation between MIC and width of zone diameter

44
Q

Two types of error in testing with MIC and disc susceptibility

A

1) False susceptible

2) False resistant

45
Q

Worse type of error

A

False susceptible

Results in patient being given an antimicrobial that isn’t effective

46
Q

Less severe type of error

A

False resistant

Results in patient being denied an effective antibiotic, but given a similarly effective one instead

47
Q

What is a false susceptible result?

A

When there is a high MIC, but large zone diameter.
MIC correctly reflects bacterial susceptibility.
Will result in an ineffective antimicrobial testing as efective

48
Q

What is a false resistant result?

A

When there is a low MIC, but a small zone diameter.
MIC correctly reflects bacterial susceptibility
Will result in an effective antimicrobial testing as ineffetive

49
Q

Acceptable error for false susceptible

A

Under 1%

50
Q

Acceptable error for false resistant

A

Under 4%

51
Q

Drawbacks of E test strip

A

Expensive, because under intellectual property

Bacteriology (29 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions