Comparison of the accuracy of disk diffusion zone diameters obtained by manual zone measurements to that by automated zone measurements to determine antimicrobial susceptibility

• Published in: Journal of microbiological methods 2008-10, Vol.75 (2), p.177-181
• Main Authors: Lestari, Endang Sri, Severin, Juliëtte A., Filius, P. Margreet G., Kuntaman, Kuntaman, Offra Duerink, D., Hadi, Usman, Wahjono, Hendro, Verbrugh, Henri A.
• Format: Article
• Language: English
• Subjects: Anti-Bacterial Agents - pharmacology; Antimicrobial susceptibility; Automation; Bacteriological methods and techniques used in bacteriology; Bacteriology; Biological and medical sciences; Disk diffusion; Disk Diffusion Antimicrobial Tests - methods; Enterobacteriaceae; Enterobacteriaceae - drug effects; Escherichia coli; Fundamental and applied biological sciences. Psychology; Humans; Image Processing, Computer-Assisted - methods; Indonesia; Microbiology; Netherlands; Quality Control; Reproducibility of Results; Staphylococcus aureus; Staphylococcus aureus - drug effects
• ISSN: 0167-7012; 1872-8359
• DOI: 10.1016/j.mimet.2008.05.020

Although a variety of techniques are available for antimicrobial susceptibility testing, disk diffusion methods remain the most widely used. We compared the accuracy of disk diffusion zone diameters as obtained by manual zone measurements in a low resource country (Indonesia) to that by automated zone measurements (Oxoid aura image system) in a high resource setting (the Netherlands) to determine susceptibility categories (sensitive, intermediate susceptible or resistant). A total of 683 isolates were studied, including 294 Staphylococcus aureus, 195 Escherichia coli and 194 other Enterobacteriaceae. Antimicrobial agents included tetracycline, oxacillin, gentamicin, erythromycin, trimethoprim/sulfamethoxazole and chloramphenicol for S. aureus and ampicillin, gentamicin, cefotaxime, ciprofloxacin, trimethoprim/sulfamethoxazole, and chloramphenicol for E. coli and other Enterobacteriaceae. Of the 4098 drug–organism combinations, overall category agreement (CA), major discrepancy (MD) and minor discrepancy (mD) between the two methods were 82.4% (3379/4098), 6.0% (244/4098) and 11.6% (475/4098), respectively. One hundred and sixty three of 244 MDs were resolved using reference broth microdilution method. Overall very major error (VME), major error (ME) and minor error (mE) of manual zone measurement were 28.8%, 45.4% and 4.9%, respectively and for the aura image system 4.9%, 16.0% and 4.9%, respectively. The results of this study indicate that the disk diffusion method with manual zone measurement in Indonesia is reliable for susceptibility testing. The use of an automated zone reader, such as the aura image system, will reduce the number of errors, and thus improve the accuracy of susceptibility test results for medically relevant bacteria.