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Prof. Dr. Sevgi ERTUĞRUL KARATAY

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Prof. Dr. Sevgi ERTUĞRUL KARATAY

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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.

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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.

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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.

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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 .

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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

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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

PC: Positive control NC: Negative control

Please write the results of the microdilution test above, specifying the MIC

values for each row separately.

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Antibiogram Tests NOTE:

Antibiogram tests can be performed with automated systems such as VITEK or other commercial kits.

These methods are frequently used in medicine,

antibiotic research and development.

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