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Comparative Study
. 2016 Sep;86(1):40-3.
doi: 10.1016/j.diagmicrobio.2016.04.016. Epub 2016 Apr 28.

A comparison of agar dilution with the Calibrated Dichotomous Sensitivity (CDS) and Etest methods for determining the minimum inhibitory concentration of ceftriaxone against Neisseria gonorrhoeae

Rodney P Enriquez  1 , Namraj Goire  2 , Ratan Kundu  1 , Barrie J Gatus  3 , Monica M Lahra  4
Affiliations
Comparative Study

A comparison of agar dilution with the Calibrated Dichotomous Sensitivity (CDS) and Etest methods for determining the minimum inhibitory concentration of ceftriaxone against Neisseria gonorrhoeae

Rodney P Enriquez et al. Diagn Microbiol Infect Dis. 2016 Sep.

Abstract

Objectives: The objective of this study was to compare the Calibrated Dichotomous Sensitivity (CDS) based agar dilution (CDS AD) method with the Etest (bioMérieux SA) methods using 2 method protocols for determining the minimum inhibitory concentration (MIC) of ceftriaxone against Neisseria gonorrhoeae. The two method protocols were the manufacturer's protocol for which the Clinical and Laboratory Standards Institute (CLSI) interpretative criteria for Neisseria gonorrhoeae could be applied, and the CDS-adapted protocol. Comparability of MIC data is critical for situation analysis and monitoring trends in global antimicrobial analysis.

Methods: Two hundred and forty eight clinical isolates of N. gonorrhoeae and the World Health Organisation (WHO) N. gonorrhoeae reference strains were tested using the three methods.

Results: When compared, CDS AD and CDS Etest gave a regression R(2) value of 94%, the Pearson's correlation coefficient was 97% and a paired comparison within one log2 dilution was 98%. The CDS AD and the Etest (CLSI) comparison gave a regression R(2) value of 90%, a Pearson's correlation coefficient of 95% and a paired comparison within one log2 dilution was 98%. The comparison of the CDS Etest and CLSI Etest gave a regression R(2) value of 91%, a Pearson's correlation coefficient of 95% and a paired comparison within one log2 dilution of 99%. Importantly, there was robust agreement between all three methods for the categorization of susceptibility of Neisseria gonorrhoeae isolates using the WHO nominated breakpoint for decreased susceptibility to ceftriaxone (≥0.125 μg/mL).

Conclusions: The CDS Etest method is comparable to agar dilution and the Etest methods for determining the MIC of ceftriaxone against N. gonorrhoeae.

Keywords: Agar dilution; CDS; CLSI; Ceftriaxone; Etest; MIC; Neisseria gonorrhoeae.

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