JAC Advance Access originally published online on July 12, 2007
Journal of Antimicrobial Chemotherapy 2007 60(3):652-654; doi:10.1093/jac/dkm256
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Rapid detection of extended-spectrum ß-lactamase-producing Gram-negative bacilli in blood cultures
Department of Microbiology, City Hospital, Dudley Road, Birmingham B18 7QH, UK
Received 21 February 2007; returned 25 March 2007; revised 14 June 2007; accepted 21 June 2007
* Corresponding author. Tel: +44-121-507-4228; Fax: +44-121-551-7763; E-mail: nigel.brenwald{at}swbh.nhs.uk
Objectives: Conventional detection of extended-spectrum ß-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 ß-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.
Keywords: HMRZ-86 , bacteraemia , chromogenic cephalosporin