A selective screening broth for rapid detection of extended-spectrum lactamases
Abstract number: P635
Objectives: The objective was to develop a rapid method of screening hospital patients for ESBL carriage. Development of a selective ESBL broth, which changes colour (red to yellow) in the presence of an ESBL, enables the detection and presumptive identification of an ESBL-producing organism.
Methods: A total of 264 controls were used to evaluate the screening broth. This included; 160 phenotypically confirmed ESBL-producing organisms and 104 negative controls. In addition, 5 NCTC and ATCC organisms were also tested against the broth.
The broth was tested against 510 unknown clinical samples (groin swabs). After overnight incubation positive broths were subcultured in order to test for ESBL production. The broth was centrifuged and the deposit tested with the chromogenic cephalosporin HMRZ-86 (Kanto Chemical Company, Japan). A coloured reaction (yellow to red) is produced in the presence of an ESBL enzyme within 15 min. A positive result was then followed by neutralisation with clavulanic acid to presumptively confirm ESBL. The Jarlier test was used to detect ESBL production and all isolates were identified by the VITEK2 (bioMérieux, France). Groin swabs were also cultured onto a growth control (MacConkey agar, Oxoid, England) for isolation of any Enterobacteriaceae; all isolates were identified by the VITEK2, and checked for ESBL production. A subset of 139 clinical samples were incubated and examined after a 4 h period.
Results: A total of 48 ESBL-producing isolates were detected from the clinical samples. The broth alone detected all 48 ESBL-producing isolates, resulting in 100% sensitivity, however the specificity of the broth was low (84.2%) due to 73 false positives. This resulted in a low positive predictive value (PPV) of 39.6%. The combined use of the broth and HMRZ-86 neutralisation test improved the specificity (98.9%), and PPV (89%) of the test. The resulting sensitivity of the test was reduced to 85.4%. Clinical samples tested at a 4 h incubation period showed that 40% of positive broths contained an ESBL-producing organism, confirmed by the HMRZ-86 neutralisation test.
Conclusion: The combined use of the ESBL broth with the HMRZ-86 neutralisation test provides a specific and relatively sensitive method for the presumptive detection of ESBL-producing organisms. There is also the potential for the ESBL broth to be used as a rapid 4 h test.
|Session name:||Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases|
|Location:||Vienna, Austria, 10 - 13 April 2010|
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