05/16/2018

Antibiotic resistance - quick and reliable detection



Early detection of antibiotic resistant pathogens can be life-saving. DZIF-scientists at the Institute for Medical Microbiology, Immunology and Hygiene, University of Cologne, have developed an antibody-based diagnostic test, which can identify carbapenem-resistant Acinetobacter baumannii bacteria in only 10 minutes - in a process similar to a pregnancy test.

Acinetobacter baumannii is a hospital-acquired pathogen and a serious threat especially in intensive care units worldwide. It is a major cause of pneumonia and bloodstream infections but can also cause meningitis and infect wounds. Multidrug-resistant strains are occurring more frequently especially in Asia, South America, North Africa and Southern Europe. Of major concern is the fact that the use of the gold standard treatment -carbapenems- is under threat, and carbapenem-resistant A. baumannii often cause outbreaks. The bacteria produce an enzyme, called carbapenemase, which destroys the antibiotic. For this reason, carbapenem-resistant A. baumannii is now top of the WHO list of antibiotic-resistant priority pathogens.

Detection of carbapenem-resistance in clinical isolates using standard diagnostic methods can take up to two days. Only then will the attending physician know if carbapenem treatment will be successful or not, and if they have to take special infection control measures to prevent the spread of the pathogen. Therefore there is a need for a fast and reliable diagnostic tool to detect carbapenem resistant bacteria as rapidly as possible to avoid inappropriate therapy. For this reason an interdisciplinary team of DZIF-scientists (microbiology, immunology and molecular biology) in cooperation with the Belgian company Coris BioConcept have developed a diagnostic kit.

Antibodies as sleuths

The scientists identified OXA-23 as the carbapenemase which is responsible worldwide for 80 % of all carbapenem-resistant A. baumannii. "A couple of years ago we have also observed that OXA-carbapenemases are highly expressed in order to be effective", explained Dr Higgins from the University of Cologne. "This relatively high concentration of OXAs allowed us to generate and utilise antibodies against OXA-23 for its detection", added Dr Klimka. This idea, which they followed up together with Dr Sonja Mertins, also from the University of Cologne, led to the development of the 10-minute test for carbapenem-resistant A. baumannii.

The expression and purification of the enzyme and the generation of OXA-23 specific, monoclonal antibodies was performed at the University of Cologne. The production of the antibody-based diagnostic kit and its distribution is in the hands of the Belgian company Coris BioConcept, which will launch the product in July 2018. "Our assay does not require expensive equipment or special training to use. The chromatographical method is quick, sensitive and specific", stated Dr Pascal Mertens from Coris BioConcept.

Quick and easy: Resistance revealed

"I like to compare it with a pregnancy test; it is similar to use and as simple to interpret the result", explains Dr Higgins. And this is how the test works: the bacteria, which was isolated from a patient e.g. a pneumonia, is lysed in a solution and drops of the lysate are added to the test strip. The lysate is drawn through the test strip by capillary forces where it meets the two OXA-23 specific antibodies, which bind to two separate epitopes of the enzyme. Only if the double-binding occurs does a coloured band appear on the test strip. With this information, the attending physician can seek alternative therapies and introduce special infection control measures. "We have shown that the test is 100 % specific for OXA-23 mediated carbapenem-resistance and with a very high sensitivity. These are features that are not commonly found in more sophisticated methods and in such a short time." stated Dr Mertins. The OXA-23 assay is the first product from the University of Cologne team. They are currently working on the generation of antibodies against the A. baumannii-associated carbapenemases OXA-40 and OXA-58. "Our goal is a rapid triple-OXA-assay, which will detect over 95 % of carbapenem-resistant A. baumannii worldwide." said Dr Klimka. The project is funded by DZIF.

Source: German Centre for Infection Research