Transcript Practical General Microbiology Lab

Tube dilution tests
A series of culture tubes are prepared, each containing a liquid
medium and a different concentration of a chemotherapeutic
agent. The tubes are then inoculated with the test organism and
incubated for 16-20 hours at 35C. After incubation, the tubes are
examined for turbidity (growth).
Minimum Inhibitory Concentration (MIC):
Is the lowest concentration of chemotherapeutic agent capable
of preventing growth of the test organism.
Minimum Bactericidal Concentration (MBC):
Is the lowest concentration of the chemotherapeutic agent that
results in no growth (turbidity) of the subcultures.
The agar diffusion test (Bauer-Kirby test):
In this test, the in vitro response of bacteria to a standardized
antibiotic-containing disc has been correlated with the clinical
response of patients given that drug.
The MIC for each agent was then compared to the usually-attained
blood level in the patient with adequate dosage. Categories of
"Resistant,“ "Intermediate," and "Sensitive" were then
established.
Disk-Diffusion Test
Epsilo-meter test
• It’s a new technique for direct detection of MIC, a
graduated increasing concentration of the antibiotic is
fixed along a rectangular plastic test strip which is
applied to the surface of an inoculated agar plate,
after over night incubation a tear drop shaped
inhibition zone is seen.
• The zone edge intersect the graded test strip at the
MIC of the antimicrobial.
E Test
E Test
Effects of Combinations of Drugs
• Synergism occurs when the effect of two drugs
together is greater than the effect of either alone.
• Antagonism occurs when the effect of two drugs
together is less than the effect of either alone.
Kirby-Bauer animation