Challenges to accurate susceptibility testing and interpretation of XXXX resistance in Enterobacteriaceae: results of a Spanish multicentre study.

@entity3477 @entity5176 @entity802 @entity800 @entity1536
OBJECTIVES: The objective of this study was to evaluate the proficiency of Spanish laboratories with respect to accurate susceptibility testing and the detection and interpretation of @entity1536 resistance phenotypes in Enterobacteriaceae. METHODS: Thirteen strains of Enterobacteriaceae were sent to 62 participating centres throughout Spain; strains harboured GyrA/ParC modifications, reduced permeability and/or plasmid-mediated @entity1536 resistance genes. The centres were requested to evaluate @entity802 and five @entity5176 , provide raw/interpreted clinical categories and to detect/infer resistance mechanisms. Consensus results from reference centres were used to assign minor, major and very major errors (mEs, MEs and VMEs, respectively). RESULTS: Susceptibility testing in the participating centres was frequently performed using the MicroScan WalkAway, Vitek 2 and Wider systems (48%, 30% and 8%, respectively). CLSI/EUCAST breakpoints were used in 71%/29% of the determinations. The percentage of VMEs for all @entity5176 was well below 2%. Only @entity800 and @entity3477 showed higher values for raw VMEs (6.6%), which decreased to 0% and 2.9%, respectively, in the interpreted VMEs. These errors were particularly associated with the CC-03 strain [qnrS2+aac(6')-Ib-cr]. For MEs, percentages were always <10%, except in the case of @entity800 and @entity802 . There was a significantly higher percentage of all types of errors for strains whose MICs were at the border of clinical breakpoints. CONCLUSIONS: The use of different breakpoints and methods, the complexity of mutation-driven and transferable resistance mechanisms and the absence of specific tests for detecting low-level resistance lead to high variability and represent a challenge to accuracy in susceptibility testing, particularly in strains with MICs on the border of clinical breakpoints.
