Antibiotic sensitivity test (AST method)
These test are useful for clinician and act as routine laboratory procedure in diagnostic bacteriology.
Type of Antibiotic sensitivity test
1. Disc diffusion test
2. Dilution test
a. Tube dilution test
b. The agar dilution test
1. Disc Diffusion test
Classic qualitative method to test susceptibility of pathogen to antibiotic by kirby-Bauer discs Diffusion test.
Uses
In this test is done after isolation of pathogenic bacteria from clinical specimen.
2. Dilution test
Minimal inhibitory concentration (MIC)
Quantitative method and uses a dilution technique.
Uses
MIC test may be necessary for patient who either fail to respond to antimicrobial therapy or who relapse during therapy.
Antibiotic sensitivity test
1. Diffusion
a. Kirby-Bauer method
b. Stokes method
2. Dilution
a. Tube dilution
b. Agar dilution
3. Diffusion and dilution
E- test
Disc Diffusion Test
Clinical material is directly incubated uniformly on surface of solid plate and discs of antibiotics are applied in it.
Observation and Result
1. If microorganisms shows growth occurs around antibiotic disc.
It shows resistance of organisms to drug. Bacteria are sensitive to antibiotics C and D but resistant to A, B and E.
2. On the other hand, absence of growth shown by zone of growth inhibition around antibiotic disc, indicate sensitivity of microorganisms to that antibiotic.
Size of zone of growth inhibition influenced by concentration and rate of diffusion of antibiotic on disc.
2. Minimal inhibitory concentration (MIC) dilution test
Dilution susceptibility testing methods are used to determine minimal concentration of antimicrobial to inhibit or kill microorganisms.
This can be achieved by dilution of antimicrobial in either;
1. Agar media or
2. Broth media
In some clinical cases, minimal bacterial concentration may need to determined. This is lowest concentration of antibiotic that kills 100% of bacteria rather than simply inhibition growth.
Tube dilation method
1. Make use of tubes containing two fold serial dilation of antibiotic agents in liquid growth medium.
A known quantity of suspended bacteria is added to each solution.
After 24 hours of incubation, the bacterial growth is measured by turbidity with the tubes.
Which given MIC value
Primary advantage of this method is ability to obtain quantitative MIC values, as well as minimum bactericidal concentration, which is lowest amount of drug at which 99% of bacteria is killed.
0 Comments