Objectives: Antimicrobial Susceptibility Test Exercise 7-3

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1

zone of inhibition

If an antibiotic stops the bacteria from growing or kills the bacteria, there will be an area around the wafer where the bacteria have not grown enough to be visible.

2

chemotherapeutic drugs

the use of drugs to treat disease

3

antibiotics

natural antimicrobial agents produced by microorganisms

4

antimicrobials

substances used to treat and kill bacterial infections. Interfere with the growth of microbes within a host

5

selective toxicity

Selective toxicity is the ability of a chemical or drug to kill a microorganism without harming its host.

6

bacterial lawn

term used by microbiologists to describe the appearance of bacterial colonies when all the individual colonies on a petri-dish agar plate merge to form a field or mat of bacteria

7

-static

stops microbes from growing but do not kill them. The microbes are there and if you take the treatment away, they can resume growth.

8

-scidal

kill microbes

9

MIC

Minimum inhibitory concentration - What is the minimum dose we need to have to prevent microbial growth. Doesn’t tell you one particular aspect: did we kill the microbes or did we just stop them from growing?

10

Identify the factor that the Kirby-Bauer antibiotic disk diffusion test is designed to evaluate

measures the effectiveness of antibiotics against pathogenic microorganisms

11

Identify variables in this method of antibiotic testing that the Kirby-Bauer method eliminates (controls). Your lab book identifies seven

1. use of mueller-hinton agar- 7.2-7.4 PH
2. Depth of agar used 4mm in 150mm or 100mm Petri dishes
3. use of 0.5 McFarland turbidity Standard for broth culture
4. Disks dispensed onto inoculated plate
5. Temperature at which incubated 35C
6. Time incubated 16-18 hours
7. Clear zones measured after incubation

12

Identify bacterial and fungal species which are known for production of antibiotics. List the three genera that produce most antibiotics and one antibiotic originally isolated from each of the genera

Penicillium (fungal)- penicillin
Streptomyces (fungal) - streptomycin
Bacillus (bacterial) - bacitracin

13

Summarize and give an example of how most antibiotics accomplish selective toxicity

Selective toxicity relies upon differences between the structure and metabolism of the patient's cells and the structure of the microbe being targeted.

They interfere with pathway with cell wall synthesis. since mammals don't have cell walls.
Also interfere with the nucleic acid and protein synthesis.

14

Broad spectrum antibiotics

effective against many types of microbes and tend to have higher toxicity to the host.

15

Narrow spectrum antibiotics

effective against a limited group of microbes and tend to exhibit lower toxicity to the host