| CORRESPONDENCE |
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| Year : 2003 | Volume
: 21
| Issue : 4 | Page : 293 |
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An innovative template for disk diffusion testing
RP Karyakarte , JK Bajaj
Department of Microbiology, Government Medical College, Aurangabad - 431 001, Maharashtra, India
Correspondence Address:
Department of Microbiology, Government Medical College, Aurangabad - 431 001, Maharashtra, India
How to cite this article:
Karyakarte R P, Bajaj J K. An innovative template for disk diffusion testing. Indian J Med Microbiol 2003;21:293 |
Dear Editor,
Kirby-Bauer method is the most popular disk diffusion method used for antimicrobial susceptibility testing. This method was subsequently modified by the NCCLS.[1] In this method the diameter of inhibition zone around the antimicrobial disk is measured to the nearest millimeter. However, this method takes a long time when large number of antimicrobial susceptibility tests are performed in clinical laboratories. We have devised a template to reduce this time. This template also makes it easy to apply the disks on the inoculated sensitivity plates and interpret the susceptibility testing results.
The template was prepared on a black card paper. A circle of 90 mm diameter (Petri Plate circle, PC) was drawn with a white pen on this paper. Seven circles of 6 mm diameter (Disk Circle, DC) were drawn inside the PC. Each DC depicts the location for the placement of antimicrobial disk. The centre of each DC is 15 mm away from the margin of PC. The selection of antimicrobials was according to the species and the clinical specimen. The standard code of the antimicrobials (as specified in the WHONET)[2] was written in appropriate DC. Two additional circles were drawn outside each DC. The inner (IC) of these two circles showed the size of the resistance value for that specific antimicrobial whereas the outer circle (OC) indicated the sensitive value [Figure:1].
Interpretation of the results was as follows:
Sensitive (S) : If the inhibition zone diameter is equal to or more than that of the OC
Resistant (R) : If the inhibition zone diameter is equal to or less than that of the IC.
Intermediate (I) : If the inhibition zone diameter is between OC and IC.
To determine the utility, the template was compared with the routine NCCLS method. The antimicrobial susceptibility testing results obtained by both the methods were same. In addition, the use of template led to significant reduction (more than half) in the time required for application of disks and for the interpretation of antimicrobial susceptibility testing results.
| ~ References | |  |
| 1. | National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial disk susceptibility tests. Approved standard M2-A7, 2000. Wayne, PA, NCCLS 2000.  |
| 2. | O'Brien TF, Stelling JM. WHONET: An information system for monitoring antimicrobial resistance. Emerging infectious diseases 1995;1:66. |
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