Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2010 Dec;48(12):4445-52.
doi: 10.1128/JCM.01101-10. Epub 2010 Oct 6.

Normalized resistance interpretation as a tool for establishing epidemiological MIC susceptibility breakpoints

Göran Kronvall  1
Affiliations

Normalized resistance interpretation as a tool for establishing epidemiological MIC susceptibility breakpoints

Göran Kronvall. J Clin Microbiol. 2010 Dec.

Abstract

Normalized resistance interpretation (NRI) utilizes the fact that the wild-type population on the sensitive side is not affected by resistance development, and therefore a normalized reconstruction of the peak can be performed. The method was modified for MIC distributions by the introduction of helper variables, in-between values assigned the mean of the neighboring numbers of isolates. This method was used on Staphylo- coccus aureus and Escherichia coli MIC distributions for 27 antimicrobials each and obtained from the EUCAST (European Committee on Antimicrobial Susceptibility Testing) website (http://www.eucast.org/mic_distributions/). The number of isolates in each of the 54 distributions ranged from 40 to 124,472. NRI produced normalized distributions in all cases. Cutoff values were calculated for +2.0 and +2.5 standard deviations (SD) above the means and then rounded up to nearest regular MIC dilution step. EUCAST also show cutoff values, ECOFF values, which were used as the reference. The NRI generated +2.0 SD values showed the best agreement with 26 of 27 within ±1 dilution step and 17 exactly on the ECOFF values for Staphylococcus aureus, and 25 of 27 within ±1 dilution step and 14 right on the ECOFF values for Escherichia coli. NRI offers an objective method for the reconstruction of the wild-type population in an MIC distribution for a given bacterial species and an antimicrobial agent. This method offers a new tool in comparative susceptibility studies such as global surveillance of resistance, as well as in quality control in individual laboratories.

PubMed Disclaimer

Figures

FIG. 1.
FIG. 1.
S. aureus MIC distributions for azithromycin (A), erythromycin (B), ofloxacin (C), and tetracycline (D). Diagram bars show the percent S. aureus isolates as given on the EUCAST website. The NRI-derived normal distributions of WT isolates are indicated by line graphs.
FIG. 1.
FIG. 1.
S. aureus MIC distributions for azithromycin (A), erythromycin (B), ofloxacin (C), and tetracycline (D). Diagram bars show the percent S. aureus isolates as given on the EUCAST website. The NRI-derived normal distributions of WT isolates are indicated by line graphs.
FIG. 2.
FIG. 2.
E. coli MIC distributions for cefotaxime (A), doxycycline (B), moxifloxacin (C), and tetracycline (D). Diagram bars show the percent E. coli isolates as given on the EUCAST website. The NRI-derived normal distributions of WT isolates are indicated by line graphs.
FIG. 2.
FIG. 2.
E. coli MIC distributions for cefotaxime (A), doxycycline (B), moxifloxacin (C), and tetracycline (D). Diagram bars show the percent E. coli isolates as given on the EUCAST website. The NRI-derived normal distributions of WT isolates are indicated by line graphs.
See this image and copyright information in PMC

References

    1. Brown, D., and G. Kahlmeter. 2010. EUCAST in 2010, p. 44-45. In G. Cornaglia, P. Cologna, and D. White (ed.), ESCMID yearbook 2009/2010. European Society of Clinical Microbiology and Infectious Diseases, Basel, Switzerland.
    1. Furtado, G. L., and A. A. Medeiros. 1980. Single-disk diffusion testing (Kirby-Bauer) of susceptibility of Proteus mirabilis to chloramphenicol: significance of the intermediate category. J. Clin. Microbiol. 12:550-553. - PMC - PubMed
    1. Giske, C. G., C. Borén, B. Wretlind, and G. Kronvall. 2005. Meropenem susceptibility breakpoint for Pseudomonas aeruginosa strains hyperproducing mexB mRNA. Clin. Microbiol. Infect. 11:662-669. - PubMed
    1. Joneberg, J., M. Rylander, M. F. Galas, C. Carlos, and G. Kronvall. 2003. Analysis of parameters and validation of method for normalized interpretation of antimicrobial resistance. Int. J. Antimicrob. Agents 21:525-535. - PubMed
    1. Kahlmeter, G., and D. F. Brown. 2002. Resistance surveillance studies: comparability of results and quality assurance of methods. J. Antimicrob. Chemother. 50:775-777. - PubMed

MeSH terms

Substances