Performance of EUCAST and CLSI approaches for co-amoxiclav susceptibility testing conditions for clinical categorization of a collection of Escherichia coli isolates with characterized resistance phenotypes. (21st April 2015)

• Record Type: Journal Article
• Authors: Díez-Aguilar, María; Morosini, María-Isabel; López-Cerero, Lorena; Pascual, Álvaro; Calvo, Jorge; Martínez-Martínez, Luis; Marco, Francesc; Vila, Jordi; Ortega, Adriana; Oteo, Jesús; Cantón, Rafael
• Is Part Of: Journal of antimicrobial chemotherapy. Volume 70:Number 8(2015:Aug.)
• Page Start: 2306
• Page End: 2310
• Publication Date: 2015-04-21
• Subjects: MICs -- amoxicillin/clavulanate -- E. coli; Anti-infective agents -- Periodicals; Chemotherapy -- Periodicals; 615.58
• DOI: 10.1093/jac/dkv088
• Languages: English
• ISSNs: 0305-7453

Abstract

Abstract: Objectives: There are different methodological recommendations for in vitro testing of the co-amoxiclav combination. Performance of co-amoxiclav MIC testing for Escherichia coli by the standard ISO microdilution method (ISO 20776-1) was compared using EUCAST (fixed 2 mg/L clavulanate concentration) and CLSI (2 : 1 ratio) interpretive criteria. Methods: MICs were determined by broth microdilution using a 2 : 1 ratio and fixed clavulanate concentrations (2 and 4 mg/L) for 160 clinical E. coli isolates with characterized resistance mechanisms. Essential agreements, categorical agreements and relative errors were determined. Results: For all isolates, essential agreement between microdilution using 2 mg/L clavulanate and a 2 : 1 ratio was 25.6%. For ESBL-producing isolates, considering EUCAST breakpoints, 55% of isolates tested with 2 mg/L clavulanate were classified as resistant; conversely, 95% of isolates tested with 4 mg/L clavulanate were susceptible. When using CLSI breakpoints and a 2 : 1 ratio, 90% of isolates were susceptible and 10% were intermediate. Conclusions: Variation in the clavulanate concentration gave different susceptibility testing results, particularly among ESBL-producing E. coli isolates. The in vitro concentration of clavulanate that better correlates with clinical outcome is still under debate and should be established.