Detection of extended-spectrum beta-lactamases (ESBLs) in clinical isolates of Klebsiella pneumoniae using the ESBL NDP test and flow cytometric assay in comparison to the standard disc diffusion

This study was undertaken to evaluate the comparison among three different assays: extended-spectrum beta-lactamases (ESBL) Nordmann/ Dortet/ Poirel (NDP) test, flow cytometric assay and disc diffusion method for the detection of ESBL production. Sixty clinical isolates of Klebsiella pneumoniae were isolated from patients’ clinical samples admitted to Suez-Canal University Hospital, Ismailia Governorate. The percentages of ESBLs producing Klebsiella pneumoniae ranged from 70 to 80% by ESBL NDP and flow cytometric assays, respectively in comparison to 76.6% by disc diffusion method. The sensitivity and specificity of the three assays were evaluated and the sensitivity by ESBL NDP and disc diffusion method was 100%, while by the flow cytometric assay, it was 91.3%. The specificity of disc diffusion method in detection of ESBLs was 100%, followed by the ESBL NDP test (85.7%) and flow cytometric assay (77.8%). Kappa testing showed perfect agreement between the ESBL NDP test and disc diffusion method (kappa=0.9), while flow cytometric assay showed substantial agreement (kappa= 0.7). The ESBL NDP test offers an applicable tool for rapid detection of ESBL-production. Although, flow cytometric assay is a promising method that might be used in the clinical microbiology laboratory but there is a need for the experienced personnel along with the device.