βlasEN: Microdilution Panel for Identifying β-Lactamases Present in Isolates of Enterobacteriaceae

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Abstract
A dried investigational use-only microdilution panel named βlasEN (a short named derived from the panel’s purpose, to identify β-lactamases in Enterobacteriaceae ) containing 10 β-lactam drugs with and without β-lactamase inhibitors was developed to identify β-lactamases among clinical isolates of Escherichia coli , Klebsiella pneumoniae , Klebsiella oxytoca , Citrobacter koseri , Citrobacter freundii group, Enterobacter spp., and Serratia marcescens . The MICs obtained with a collection of 383 organisms containing well-characterized β-lactamases were used to develop numeric codes and logic pathways for computerized analysis of results. The resultant logic pathways and βlasEN panel were then used to test and identify β-lactamases among 885 isolates of Enterobacteriaceae recovered in cultures obtained at six different hospital laboratories across the United States. β-Lactamases present in 801 (90.5%) of the 885 isolates were identified by βlasEN by using the existing logic pathways and codes or after minor modifications were made to the existing codes. The 84 strains that gave codes that βlasEN could not identify were collected, reidentified, and retested by using βlasEN. Three strains had been misidentified, 54 strains gave different codes upon repeat testing that could be identified by βlasEN, and 27 strains repeated new codes. The β-lactamases in these strains were identified, and the new codes were added to the βlasEN logic pathways. These results indicate that βlasEN can identify clinically important β-lactamases among most isolates of Enterobacteriaceae . The results also show that good quality control and attention to proper performance of the tests are essential to the correct performance of βlasEN.