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Flashcards in Intro to antibacterial agents Deck (23)
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1

difference between bacteriostatic and bactericidal?

Bacteriostatic: Kill microbe
Bactericidal: Inhibits growth of microbe

2

difference between an antiseptic and a disinfectant?

Antiseptic: kill microbes topically on surface
Disinfectant: Kill microbes on inanimate objects

3

The basic target sites for the action of antibacterial agents?

1. Cell wall synthesis
2. DNA synthesis
3. RNA synthesis
4. Protein synthesis (50S + 20S ribosomes)
5. Antimetabolites: biochem. pathways

4

Difference between the MIC and the MBC for an antimicrobial agent?

MIC: Min. Inhibitory Conc. = no growth in tube
MBC: Min. Bactericidal Conc. = no growth in tube & culture plate

5

List 5 ideal qualities for an antimicrobial agent and explain the benefit of each?

1. Non-toxic to eukaryotic cells: selective toxicity
2. Broad spectrum: targets range of microbes
3. Bactericidal: Kills microbes
4. No acquired or intrinsic resistance: antimicrobial effective
5. Slow clearance time: not degraded quickly
6. Effective @ low dose: less harmful to person
7. Min. impact to host's NF:

6

Define drug Autonomy, antagonism, synergism

Autonomy: 2x anti-b have no effect on each other if tog.
Antoagonism: 2x anti-b that cancel each other if tog.
Synergism: 2x anti-b have a better effect when tog.

7

What bacterial genus has been the source of many antimicrobial agents?

*

8

Why would norfloxacin not be prescribed for septicaemia or meningitis?

*

9

Why should nitrofurans not be prescribed with quinolones?

bc antagonistic to each other

10

Adv & disadv. of nitrofurans

Adv: bactericidal
Disadv: antogonistic w/ quinilones; Only oral use; Only use for UTI

11

Why is tetracycline not used in children (unless it were a treatment of last resort)?

stain teeth of kids <8-9 yrs old during calcification

12

Adv & disadv. of tetracycline

Adv: inhibit protein synthesis; variable resistance in GPos & GNeg (susceptible)
Disadv: bacteriostatic; oral use only; stain kid's teeth;

13

Why is chloramphenicol primarily only used as a topical agent?

bc broad spectrum - can cause toxixity problems

14

Adv & disadv. of chloramphenicol

Adv: inhibit protein synthesis; suitable for oral & parenteral (IV), topical use
Disadv: bacteriostatic; broad spectrum => toxicity problems

15

What is the similarities & difference b/w ampicillin and amoxicillin?

Both: have the same bacterial activity
Amoxillin: absorbed better by GIT

16

How would aminoglycosides be administered?

IV only bc not absorbed by gut

17

Adv & disadv. of aminoglycosides

Adv: bactericidal; active against staph (not MRSA), Enterobacteria, most aerobic GNB (e.g. P. aeruginosa) inhibit protein synth.
Disadv: IV only; not active against anaerobes or streptococci;

18

Why are some bacterial agents suitable for oral ingestion and others are not?*

absorbtion in GIT*

19

Name and define the three methods of expression of enzyme induced antibacterial resistance?

- Inducible: enzyme only produced if organism is EXPOSED to corresponding B-lactam anti-b
- Consttutive: produced CONSTANTLY
- Constitutive-inducible: produced CONTANTLY @ LOW lvls & INC. as EXPOSED to anti-bact.

20

Why don’t sulphonamides, trimethoprim or their combination affect humans but do affect bacteria?

Bc these antibacterials inhibit folate pathway = bact. can’t make folate ≠ make dNTP ≠ make DNA. Humans not affected bc get folate from die

21

Explain how the CDS (Calibrated dichotomous sensitivity) method of disc susceptibility are performed.

1. Fresh colony is picked & mixed in saline.
2. innoculum is distributed evenly on sensitised agar media with excess removed.
3. It is let to dry then anti-b disk are placed on the media & inoculated for 18 hrs.
4. The radius of the disks are measured and interpreted. if <6 = Resistant. ≥6= susceptible

22

Explain how the CLSI/EUCAST method of disc susceptibility are performed.

1. Fresh colony of test organism is suspended to a density of ~0.5 McFarland std.
2. A lawn Innoculum is spread on MH agar plate in 3x directions w/ a swab dipped once in inoculum.
3. Incubated in air or CO2 for 18-24hrs.
4. Zone diameter measured in mm & use a table to determine result = susceptible, intermediate or resistant

23

Explain how to set up and read an E-test strip so as to report an MIC for gentamicin?*

*