Exercise 13: Compatative Evaluation of Antimicrobial Chemicals

chemical agents used on inanimate objects to lower the level or number of microbes on the surface.

disinfectants

chemicals used on living tissues to decrease the number of microbes.

antiseptics

Disinfectants are chemical agents used on inanimate objects to lower the level or number of microbes on the surface. In contrast, antiseptics are chemicals used on living tissues to decrease the number of microbes. Both of these classes of chemicals can affect bacteria in different ways

bactericidal agents will result in bacterial death and bacteriostatic agents inhibit the growth of cells.

What are agents will result in bacterial death

bactericidal

What are agents inhibit the growth of cells.

bacteriostatic

What does this mean:

effective against multiple types of bacteria; zones of inhibition will be similar sizes between tested organism

broad spectrum

What does this mean:

More effective against some types of organisms than others; zones of inhibition will be markedly different in size between organsims

narrow spectrum

How was the effectiveness of antimicrobial compounds determined?

The chemicals diffuse from the disk, and any effects they have on the microbes will be seen as a disruption in the lawn of cell growth.

effectiveness by measuring the zones of inhibition around each disc on plates previously inoculated with a gram positive (Staphylococcus epidermidis) and gram negative (Escherichia coli) test organisms.

Disk diffusion assay

Organism to be tested is spread on surface of agar plate

discs contiaining chemicals to be tested are placed on the surface of the agar

antimicrobial diffused through agar during incubation

if effective against the organism, a zone of inhibition will be visible after incubation

What is zone of inhibition

the clear zone surrounding an antimicrobial agent, which allows us to see the effectiveness of the antimicrobial agent

a clear zone respresenting inihibition of growth can be seen around the disk

MIC (what does the abbreviation stand for and what does it mean) finish this

Minimum inhibitory concentration

• the edge of the zone of inhibition