Use your understanding of AST as learned in the reading to answer the following:

Question

Use your understanding of AST as learned in the reading to answer the following:

Scenario: You are an IP at a 100bed hospital. Previously, your facility had sent cultures to an offsite microbiology lab in town; however, the facility has decided to begin performing onsite microbiology. The newly hired microbiology director comes to you and asks if you have preferences as to which antimicrobial susceptibility testing (AST) methodology is utilized in the laboratory as the primary method.  

Options presented are automated broth microdilution using VITEK, automated broth microdilution using Microscan (prompt method), agar/tube microdilution, e-test, or Kirby Bauer disk diffusion.  

1) Choose a method and, using the advantages and limitations of the selected method as well as the advantages and limitations of the other options, justify your selection.  

She also asks if you would want qualitative or quantitative susceptibilities displayed to providers.  

Explanation / Answer

Hi,
The AST carried out at hospital itself provides for rapid and more reliable data. Of the available tests the Kirby Bauer disk diffusion is the most appropriate one for the hospital condition. It is relatively simple, less laborious and easy to interpret. It is quanlitative where bacteria are divided into 3 groups, resistant, suscpetible, and intermiediate. This is sufficient data to decide on the type of antibiotic and its dose. One of the potential drawkback of this method is that it is time consuming. Overngiht or even upto 24 - 36 h incubation is requried to visibly seen the clearance zones on the plate. It does not give any data on the MIC of the antibiotics.

Other methods such as microdilution using VITEK, automated broth microdilution using Microscan (prompt method) are automated methods which are accurate and reliable. They give data on MIC value and many other aspects of antimicrobial efficacy. These methods are not suited in this set up because of the high cost of instrument. This would result in higher cost on the patient. The e-test is a strip based method, which is also reliable and give MIC data (quantitative). But it is very expensive.
The agar/tube microdilution is time tested method to determine the Antimicrobial sensitivity and also MIC of the antibiotics. This is time consuming and laborious.
From the above discussions, we can go ahead to Kirby Bauerdisk diffusion method which is qualitative and provides data sufficient enough to decice on the antibiotic treatment regime.

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