Rapid detection of extended-spectrum β-lactamase-producing Gram-negative bacilli in blood cultures

Abstract

Objectives: Conventional detection of extended-spectrum β-lactamase (ESBL) producers in blood cultures usually requires overnight incubation. This could delay the prescribing of appropriate therapy. We evaluated whether the chromogenic cephalosporin HMRZ-86, which is hydrolysed by ESBLs, could be used for the rapid detection of ESBL producers directly in blood culture broths. Methods: The HMRZ-86 test was first applied to broth cultures of isolates producing known β-lactamases. A colour change indicating hydrolysis, which was inhibited by clavulanic acid, was taken as an indication of ESBL production. A similar method was used for testing blood culture supernatants and broth subcultures of blood cultures. Results: The HMRZ-86 test detected all the ESBL producers among 83 clinical isolates and control strains. Only one false positive was seen. The usefulness of HMRZ-86 for the direct testing of blood culture broths was limited by the presence of lysed blood. However, by using a 2 h broth subculture of the blood culture broths, the HMRZ-86 test was able to detect all those blood cultures containing an ESBL producer. No false positive or negative tests occurred according to the results of our standard phenotypic tests. Conclusions: The HMRZ-86 test is a simple and rapid method that can be used for detecting ESBL producers in blood cultures. © The Author 2007. Published by Oxford University Press on behalf of the British Society for Antimicrobial Chemotherapy. All rights reserved.