Objectives: Antimicrobial Susceptibility Test Exercise 7-3
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.
the use of drugs to treat disease
natural antimicrobial agents produced by microorganisms
substances used to treat and kill bacterial infections. Interfere with the growth of microbes within a host
Selective toxicity is the ability of a chemical or drug to kill a microorganism without harming its host.
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
stops microbes from growing but do not kill them. The microbes are there and if you take the treatment away, they can resume growth.
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?
Identify the factor that the Kirby-Bauer antibiotic disk diffusion test is designed to evaluate
measures the effectiveness of antibiotics against pathogenic microorganisms
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
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
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.
Broad spectrum antibiotics
effective against many types of microbes and tend to have higher toxicity to the host.
Narrow spectrum antibiotics
effective against a limited group of microbes and tend to exhibit lower toxicity to the host