Prospective evaluation of an algorithm for the phenotypic screening of carbapenemase-producing Enterobacteriaceae

Objectives: The objective of this study was to assess the performance of an algorithm based on the disc diffusion method for the screening of carbapenemase-producing Enterobacteriaceae (CPE) referred to the French National Reference Centre for Antibiotic Resistance. Methods: From April to June 2014, all isolates of Enterobacteriaceae referred to the French National Reference Centre for Antibiotic Resistance were included. The inhibition zone diameters of imipenem, ticarcillin/clavulanate and temocillin using EUCAST disc diffusion methodology were recorded. All isolates were subjected to the algorithm proposed by the Antibiogram Committee of the French Society of Microbiology (CA-SFM) for the screening of carbapenemase producers. Phenotypic, biochemical and molecular detection of carbapenemases was performed for all isolates. Results: A total of 621 consecutive enterobacterial isolates with decreased susceptibility to carbapenems were tested. They included 213 CPE [OXA-48-like (n=183), NDM (n=22), VIM (n=3), KPC (n=3) and OXA-48-like+NDM (n=2)] and 408 non-carbapenemase producers. The CA-SFM algorithm combining cut-off values of 15 mm, 15 mm and 22 mm for ticarcillin/clavulanate, temocillin and imipenem, respectively, perfectly detected 204 isolates (32.8%) as non-carbapenemase producers, leading to a negative predictive value of 100% for this algorithm. Conclusions: Implementation of the CA-SFM algorithm in clinical microbiology laboratories may avoid additional testing for CPE in one-third of the enterobacterial isolates with decreased susceptibility to carbapenems.