The document discusses various methods for antibiotic sensitivity testing, including Kirby Bauer disk diffusion, comparative methods, dilution methods, and Epsiloid tests. The Kirby Bauer method involves placing antibiotic disks on an inoculated agar plate and measuring inhibition zones. The comparative method compares inhibition zones to a control, classifying sensitivity as sensitive, intermediate, or resistant. Dilution methods detect the minimum inhibitory concentration by making serial dilutions of antibiotics and observing bacterial growth. Epsiloid tests also detect minimum inhibitory concentrations using plastic strips containing exponential gradients of antibiotics.

1. Antibiotic sensitivity testing

2.  The antibiotic sensitivity test is the best method to
select proper treatment of infectious diseases
 So, we use it either to
 1- select the best antimicrobial agent
 2-to accumulate epidemiological information on the
resistance of microorganism of public health
importance

3. 1. Kirby Bauer agar disk diffusion
methods
 Procedure
 1-Streak bacterial inoculum on (Mueller-Hinton agar
plate )
 2- antibiotic impregnated discs are placed onto the
agar surface
 3-incubate over night on 37 ºc
 4- an inhibitory zone appear around the disks
 5- zone of inhibition is measured according to
National Committee for Clinical Laboratory
Standards (NCCLS).guidelines

8. 2.
comparative methods (Stokes’)
 - Both the test and the control organism are
inoculated on the same plate using an inoculums
which gives semi-confluent growth (neither too
heavy or too light).
 Interpretation of the result
 - Sensitive(S): zone radius is wider than or equal
to or not more than 3mm smaller than the control.
 - Intermediate (I): zone radius is more than 3mm
and smaller than the control but not less than 3mm.
 - Resistant(R): No zone of inhibition or zone
radius measure 2mm or less.

10. 3. Dilution method
 - This used to detect antimicrobial susceptibility to
slow growing M.O.
 - It could be carried out on microtiter plate or test
tube.
 - It used to detect MIC
 - Performed by making a serial dilution of
antimicrobials in broth media and add 5 drops from
106bacterial suspensions and incubate at 37 °C over
night, then read about turbidity which indicates resistance
and clearance which indicate sensitivity, and detect the
MIC as the lowest concentration of antimicrobial that
required preventing visible growth.
 -

12. 4. Epsiloid test (E test):
- Used for detection of MIC in plate procedure.
- We could detect more than one MIC at the same time.

13. 
Epsilometer test (E- test ) is an ‘exponential gradient’
method of determination of antimicrobial resistance.
The E-test has been developed to provide a direct
quantification of antimicrobial susceptibility of
microorganisms.This is a quantitative method that
applies both the dilution of antibiotic and diffusion of
antibiotic into the medium.

14. 
The device consists of a predefined, continuous, and
exponential gradient of antibiotic concentrations
immobilized along a rectangular plastic test strip.
After 48 hours incubation a drop-shaped inhibition
zone intersects the graded test strip at the inhibitory
concentration (IC) of the antibiotic.