Pam Harrison

April 15, 2014

CAPE TOWN, South Africa — A biochemical test that can rapidly identify extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae in a blood culture is 100% accurate on all fronts, new research shows. It could soon be ready for clinical use.

"The reasons we developed this test were, first, to identify ESBL-producing bacteria — mostly Klebsiella pneumoniae that could be the source of an outbreak," said Patrice Nordmann, MD, PhD, professor and chair of microbiology at University of Fribourg in Switzerland. "Second, we developed the test to treat patients with carbapenem when they need it."

"Of all the research we've done over the past 25 years, this is the most important," he told Medscape Medical News.

Dr. Nordmann presented the results here at 16th International Congress on Infectious Diseases.

Blood Cultures

The investigators used the ESBL Nordmann/Dortet/Poirel (NDP) test to prospectively detect ESBL-producing Enterobacteriaceae in blood cultures from November 2012 to May 2013. (The test is named after its developers: Dr. Nordmann and his colleagues Laurent Dortet, PhD, from Hôpital de Bicetre in France, and Laurent Poirel, PhD, from the University of Fribourg.)

ESBLE NDP test results were compared with those obtained using double disk diffusion techniques.

All 96 blood cultures analyzed were tested for Gram-negative organisms using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) technology, and results were confirmed with biochemical identification. All tested positive.

The ESBL NDP test detected 18 blood cultures that were infected with ESBL-producing Enterobacteriaceae; 15 were CTX-M-producing Escherichia coli and 3 were CTX-M-producing K pneumoniae.

The remaining 78 cultures were infected with non-ESBL-producing isolates, and the ESBL NDP test results were negative.

"The main advantage of the ESBL NDP test is that you can obtain results in 20 minutes, compared with 24 to 48 hours for standard tests," Dr. Nordmann explained. In addition, the sensitivity, specificity, negative predictive value, and positive predictive value of the test are all 100%.

"Because the successful treatment of septicemia depends on the prompt administration of the appropriate agent, the ESBL NDP test could significantly improve the outcome of infected patients," he said.

Easy Technology

The technology behind the test is "very easy," said Dr. Nordmann.

A blood sample is processed in a centrifuge and a protein extract is obtained. This protein is put into a tube with cefotaxime, a beta lactam, and a pH indictor (red phenol). If the protein causes cefotaxime to hydrolyze, "you have production of an acid and the pH indicator will go from red to yellow," he explained.

Because tazobactam inhibits the activity of ESBL-producing organisms, the addition of tazobactam to a complementary well indicates the presence of an enzyme that hydrolyzes the extended-spectrum cefotaxime. This confirms the presence of an ESBL-producing organism.

The research team has been using the ESBL NDP test in a busy academic hospital in Paris on a daily basis for the past 12 months. "On a regular day, we have perhaps 4 to 6 positive cultures with Gram-negative bacteria," Dr. Nordmann told Medscape Medical News.

The team also developed the Carba NP test for the early detection of carbapenem-resistant Enterobacteriaceae.

The Carba NP test uses imipenem as a substrate instead of cefotaxime and detects carbapenemase production in isolated colonies; otherwise, it relies on the same biochemical principles as the ESBL NDP test.

Anyone interested in making their own ESBL NDP or Carba NP test is invited to contact Dr. Nordmann directly.

The cost-effective and rapid detection of ESBL-producing Enterobacteriaceae directly in blood cultures should help decrease morbidity and mortality resulting from infections caused by these types of bacteria, said Johann Pitout, MD, professor of pathology and laboratory medicine at the University of Calgary in Alberta, Canada.

"The ESBL NDP phenotypic performed admirably in detecting ESBL-producing Enterobacteriaceae in this study," he told Medscape Medical News. "Investigators were able to rapidly detect 100% of ESBL-producing isolates causing bloodstream-associated infections."

However, a study with an outcomes-based approach that documents the effects of rapid testing on morbidity and mortality, as well as on antibiotic stewardship programs at large, is needed, said Dr. Pitout.

According to Dr. Nordmann, plans for such a follow-up study are currently underway.

Dr. Nordmann and Dr. Pitout have disclosed no relevant financial relationships.

16th International Congress on Infectious Diseases (ICID): Abstract 59.012. Presented April 5, 2014.

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