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Use of Multiplex Immunochromatographic Tests for Diagnosing Bacterial Infections Highlighted in Study


NEW YORK (360Dx) – A new study has demonstrated the use of immunochromatographic assays, rather than conventional culture, to rapidly detect carbapenemases, byproducts of Enterobacteriaceae associated with increased mortality.

Using kits manufactured by Coris BioConcept, researchers at the University of Cologne were able to show that the results of the 30-minute ICT test were concordant with standard methods, which can take up to 72 hours. The results of the study were detailed recently in PLOS ONE.

Gembloux, Belgium-based Coris has manufactured ICT kits for detecting different kinds of carbapenemases since 2015. The kit used in the new study detects from an initial blood culture three carbapenemases called OXA-48-like, Klebsiella pneumoniae carbapenemase (KPC), and New Delhi metallo-betalactamase (NDM). This test, branded as the Resist-3 OKN K-Set, consists of the reagents necessary to carry out the assay, as well as the test cassettes. Coris offers a variety of similar tests that allow researchers to target their carbapenemases of choice.

The assay requires that a sample be cultured first, but rather then test that sample in subsequent blood cultures, those tests can be run directly on the ICT cassette.

"Instead of culturing on solid media and doing susceptibility tests, we can now directly detect the carbapenemase protein, and within half an hour after culture becomes positive, you can say this infection is caused by carbapenemase-producing organism," said Axel Hamprecht, a clinical microbiologist at the University of Cologne in Germany and corresponding author on the new paper.

"This makes a huge difference in terms of time for the patient;" Hamprecht said. "You can initiate therapy much earlier." He also noted that the assay is accessible to most clinical microbiology laboratories. "For adoption of this technique, all you need is a centrifuge, wet culture techniques, and the immunochromatographic assay," he said.

Researchers like Hamprecht are increasingly interested in new methods for quickly detecting carbapenemase-producing bacteria, which are considered especially difficult to treat and are often resistant to antibiotics. By determining the kind of bacteria involved in an infection earlier, they might be able to better select treatment. The US Centers for Disease Control classified such bacteria as an "immediate public health threat" in a 2013 report on antibiotic resistance.

As part of the study, Hamprecht and fellow researchers assessed 170 Enterobacteriaceae clinical isolates including 79 OXA-48-like carbapenemases, 18 KPC carbapenemases, and 29 NDM carbapenemases. Following spiking with bacteria and incubation in a blood culture system, the blood from positive samples underwent centrifugation and was lysed, and then transferred to Coris BioConcept's Resist-3 OKN K-Set and read after 15 minutes.

All of the isolates were accurately detected, meaning the test had 100 percent sensitivity and specificity. The authors concluded that the test, given its time advantage, could "optimize the management of patients with difficult-to-treat infections."

There are other tests on the market for rapid detection of carbapenemases. French diagnostic firm BioMérieux, for instance, manufactures a PCR-based test called Rapidec Carba NP that is recommended for use by the Clinical and Laboratory Standards Institute for confirming carbapenemase production. Sunnyvale, California-based Cepheid sells its Xpert Carba R Assay for use on its GeneXpert instruments. Like the BioMérieux test, that assay is also PCR based. NG Biotech, a Guipry, France-based firm, makes lateral-flow ICTs for carbapenemase detection similar to Coris'.

Hamprecht said he was inclined to adopt ICTs over culture or PCR for various reasons. "With a phenotypic test, you need about a day to get a result, whereas an immunochromatographic assay is done in one hour," he said. PCR, in his opinion, "takes a longer time and is pricier." Part of this price stems from the need for lab technicians to carry out the PCR assays, and more equipment.

"An immunochromatographic test is easy, like a pregnancy test;" said Hamprecht. "You just add your sample and solvent and read if it is positive or not," he said. "You don't need a lot of training and it can be done in any laboratory that is able of doing regular microbiology."

Jean-Marie Hoornaert, a sales manager at Coris BioConcept, said that since launching its initial carbapenemase assays in 2015, the firm has continued to innovate. Recently, the company, which employs around 30 people, launched a five-plex test spread across two cassettes rather than concentrated in one in order to make the lines on the test easier to read and reduce background noise. The main users of the firm's assays are hospital labs, bacteriology labs, and private labs, he said, with a few sales to research institutes.

"The biggest advantage is that you can start with culture and then administer the test," Hoornaert said. "The standard method is to do a first culture and then do resistance testing on a second plate."

He said that Coris BioConcept is currently at work on a new protocol that would allow testing directly on a patient swab, bypassing culture entirely. Together with an enrichment step, the assay would take about three hours to complete, versus the 24 hours required for culture methods. Hoornaert said this test should be available and CE marked for research use by year end. He said the company will also undertake a multicenter trial of the test for marketing purposes.

In order for the test to gain more widespread use, though, he said the cost of the tests must decline while reimbursement from government institutions is achieved. Currently test kits cost around 15 ($17), he said. The availability of a protocol with a short incubation, such as the one the company is developing is also necessary to building demand for the tests.

"If we take these steps it will be a real success," said Hoornaert. "The price depends on the market. And in many countries it takes time to get reimbursement for molecular tests," he said. Hoornaert said that the availability of a faster protocol would lower the price of the test as well.

The company is not without a competitor though. NG Biotech also continues to innovate on its platform, which currently includes the NG-Test CARBA5, and the firm's assay was featured in a Journal of Antimicrobial Chemotherapy paper published this year.

The work was carried out by researchers within Public Health England's Antimicrobial Resistance and Healthcare Associated Infections Reference Unit  and their partners in France. The corresponding author declined to comment on the new PLOS ONE study, noting the University of Cologne researchers had used another test.

Milovan Stankov-Puges, CEO of NG Biotech, noted that his firm's test had been co-developed with the French Alternative Energies and Atomic Energy Commission and Kremlin Bicêtre-Paris, a French reference center. He noted that at the moment, CARBA5 is the only assay available for characterizing the five main carbapenemase groups on a single test strip.

He added that the kind of testing that NG Biotech and Coris offer is "essential" at the moment.

"Awareness toward hospital-acquired infections and antimicrobial resistance is increasing worldwide," said Stankov-Puges. "The demand for rapid and easy-to-use technologies to detect and characterize AMR is increasing." he said. ICTs have an advantage in this marketplace, he added, because they do not require heavy laboratory equipment or training.

Stankov-Pulges said that NG Biotech is planning to extend its range of tests for carbapenemase-producing bacteria, but declined to discuss what targets the company is working on or to further comment on innovation in this area.