Direct detection of extended-spectrum-β-lactamase-producers in Enterobacterales from blood cultures: a comparative analysis

Accurate detection of extended-spectrum-beta-lactamase (ESBL)-producing Enterobacterales from bloodstream infection (BSI) is of paramount importance for both epidemiological and clinical purposes, especially for optimization of antibiotic stewardship interventions. Three phenotypic methods for the detection of ESBL phenotype in Klebsiella pneumoniae and Escherichia coli BSI were compared over a 4-month period (May-August 2021) in a main University Hospital from Northern Italy. The methods were the biochemical Rapid ESBL NP (R), the immunological NG-Test CTX-M MULTI (R), and the E-test technique based on ESBL E-test (R). One hundred forty-two blood cultures (BCs) positive for K. pneumoniae or E. coli were included. ESBL and carbapenemase phenotype were detected in 26.1% (n = 37) and 16.9% (n = 24), respectively. The Rapid ESBL NP (R), NG-Test CTX-M MULTI (R), and direct ESBL E-test (R) positive and negative predictive values with 95% confidence intervals were 1 (0.87-1) and 0.97 (0.92-0.99), 1 (0.87-1) and 0.97 (0.92-0.99), and 1 (0.88-1) and 1 (0.96-1), respectively. The three phenotypic methods evaluated showed good performance in the detection of ESBL phenotype from K. pneumoniae- or E. coli-positive BCs. Rapid ESBL NP (R) and NG-test CTX-M (R) offer the important advantage of a turnaround time of 15 to 45 min, and the Rapid ESBL NP test in addition detects any type of ESBL producers.