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Applied and Environmental Microbiology, April 2004, p. 2398-2403, Vol. 70, No. 4
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.4.2398-2403.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Evaluation of a Scanner-Assisted Colorimetric MIC Method for Susceptibility Testing of Gram-Negative Fermentative Bacteria

Mokhlasur Rahman,1* Inger Kühn,1 Motiur Rahman,2 Barbro Olsson-Liljequist,3 and Roland Möllby1

Microbiology and Tumor Biology Center, Karolinska Institutet, S-171 77 Stockholm,1 Department of Bacteriology, Swedish Institute for Infectious Disease Control, S-171 82 Solna, Sweden,3 International Center for Diarrhoeal Disease Research, Mohakhali, Dhaka-1212, Bangladesh2

Received 28 October 2003/ Accepted 9 December 2003

We describe the ScanMIC method, a colorimetric MIC method for susceptibility testing of gram-negative fermentative bacteria. The method is a slight modification of the National Committee for Clinical Laboratory Standards (NCCLS) recommended broth microdilution method that uses a redox indicator 2,3,5-triphenyltetrazolium chloride (TTC) to enhance the estimate of bacterial growth inhibition in a microplate and a flatbed scanner to capture the microplate image. In-house software was developed to transform the microplate image into numerical values based on the amount of bacterial growth and to generate the MICs automatically. The choice of indicator was based on its low toxicity and ease of reading by scanner. We compared the ScanMIC method to the NCCLS recommended broth microdilution method with 197 coliform strains against seven antibacterial agents. The interpretative categorical agreement was obtained in 92.4% of the assays, and the agreement for MIC differences (within ±1 log2 dilution) was obtained in 96% for ScanMIC versus broth microdilution and 97% for a two-step incubation colorimetric broth microdilution versus the broth microdilution method. The method was found to be labor-saving, not to require any initial investment, and to show reliable results. Thus, the ScanMIC method could be useful for epidemiological surveys that include susceptibility testing of bacteria.

* Corresponding author. Mailing address: Microbiology and Tumor Biology Center, Karolinska Institutet, Box 280, S-171 77 Stockholm, Sweden. Phone: 46 8 5248 71 53. Fax: 46 8 5248 7908. E-mail: mokhlasur.rahman{at}mtc.ki.se.

Applied and Environmental Microbiology, April 2004, p. 2398-2403, Vol. 70, No. 4
0099-2240/04/$08.00+0     DOI: 10.1128/AEM.70.4.2398-2403.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.





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