Antibiotic sensitivity test (Antibiogram)

Purpose of Antibiogram Test

After a medical examination your doctor may think that the cause of your problem is an infection. Some laboratory tests will be needed to diagnose the infection and to find a treatment way for it. Your doctor requests you to have a culture test to see the bacteria presence and after confirming of  bacteria some other laboratory tests should be done to plan the right treatment for you. Antibiotic sensitivity test is done to find the  sensitivity or susceptibility of bacteria to antibiotics. With antibiogram test result you’ll be able to use the correct antibiotic for causative bacteria.

antibiotic sensitivity test

Steps of Culture and Antibiotic Sensitivity Test

Culture Sample Collection: Sample is taken from the infected area carefully to avoid contamination.

Bacteria Inoculation/Caltivation: Taken culture material is inoculated in culture medium/culture media with some different tecniques, laboratory technician places culture sample by spreading it  into the culture media.

Incubation: Bacteria need optimum conditions and a certain time for growing and multiplying. Inoculated culture media is waited in certain temperature for 24-48 hours; this is called incubation process.

These first steps are called Culture Test. If  bacteria are found after the incubation process an additional laboratory test should be done to find bacteria sensitivity to antibiotics.This is antibiotic sensitivity test (AST).

Bacteria and some different kinds of antibiotics are inoculated in a special culture medium and after waiting a certain time, some antibiotics will affect the bacteria and some others won’t. So we will be able to see susceptibility or resistance of bacteria to different kinds of antibiotics.

How the Antibiogram Test is Performed

  • At the end of the culture test, grown bacteria are taken into an another liquid culture media for multiplying.
  • After multiplying process bacteria are spread on a special culture antibiogram medium.
  • Antibiotic containing small discs are placed into this bacteria inoculated medium. Sterile conditions must be cared during this process.
  • Incubation; waiting period will be for 24 hours
  • If the bacteria are sensitive to that kind of antibiotic they will die in a circular shape around the antibiotic disc, so surroundings of the antibiotic disc will be empty.
  • If the bacteria are resistant to antibiotic, around of disc will be filled up with bacteria.
  • The size of circular area may be different for different kinds of antibiotics. This size is evaluated one by one for every different kind of antibiotic.
  • According to the circular affected areas around the antibiotic discs, antibiotic sensitivity test will be done, so we will have a antibiogram report as a result of this.
  • Antibiogram report determines the antibiotics as; sensitive, less sensitive and resistant.

Antibiogram Test Report

Microbiologist evaluates antibiotic sensitivity test mediums,

Circular areas around the antibiotic discs are measured

Antibiotic names are written to the antibiogram test report as  sensitive or resistant to guide and inform your doctor about infection treatment with antibiotics.

Importance of Antibiotic Sensitivity Test

Haphazard use of antibiotics without identifying the causative bacteria and effective antibiotics cause increasing of bacteria resistance to antibiotics. This bacterial resistance cause failure of treatment and medicines become useless. New medicine research studies cost a lot of  money however with antibiotic sensitivity test the correct antibiotic for the infection would be determined easily and ineffective medication usage will be prevented. Patients will be cured faster and money loss or bacteria resistance will be prevented with usage of these laboratory tests.


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