Prof. Dr. Sevgi ERTUĞRUL KARATAY
Antibiogram Tests
Broth Microdilution Method
This method is performed in 96-well microplates and requires serial dilution.
Quantitative results can be obtained as MIC values of antibiotics against certain microorganisms can be determined as a result of two-fold serial dilution.
Although it is more sensitive than disk diffusion test,
this method is more labor intensive.
Antibiogram Tests
Application of Broth Microdilution Method Antibiotic susceptibility is prepared for the
appropriate micro-organism liquid medium (Mueller Hinton Broth-MHB) is prepared and put into
microplates.
The turbidity of the 18-24 hours liquid microorganism culture is adjusted to 0.5 McFarland.
With multi- or single-channel micropipettes, the antibiotic is placed in the microplate at the highest dose. Then the other wells are serially diluted with the
same antibiotic.
Antibiogram Tests
Application of Broth Microdilution Method
Microorganisms are inoculated in wells with micropipettes.
Microplates are incubated at 37 ºC for 18-24 hours.
After incubation, the development of the microplates is measured either on the eye or on a spectrophotometer with a microplate reader. The measured value is compared to the
standard values reported by institutions such as CLSI or EUCAST to determine whether the microorganism is
susceptible or resistant to that antibiotic.
Antibiogram Tests
Application of Broth Microdilution Method
In this experiment, wells containing no antibiotics but containing microorganisms and media are used as
positive controls.
Similarly, wells containing antibiotics and medium but without microorganisms are used as negative controls.
If there is no growth in the positive control or in the
negative control, the experiment is repeated .
Antibiogram Tests
ug/mL
11024 2
512 3
256 4
128 5
64 6
32 7
16 8
8 9
4 10
2 11
1 12
0.5
A B C D E F G
H PC PC NC NC
growth
No growth
PC: Positive control
NC: Negative control
Antibiogram tests
ug/mL
11024 2
512 3
256 4
128 5
64 6
32 7
16 8
8 9
4 10
2
A PC NC
B PC NC
C PC NC
D PC NC
E PC NC
F PC NC
G PC NC
H PC NC
Growth No growth