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“The risk of patients dying from sepsis increases the longer the diagnosis takes”

Topic of the Month February: New Diagnostic Methods


“The risk of patients dying from sepsis increases the longer the diagnosis takes”

Photo: Smiling man with glasses

Doctor Dirk Kuhlmeier;
© Fraunhofer IZI

This description is quite catchy and gives a hint what happens to patients whose sepsis is not recognized and treated at an early stage - they are in mortal danger within a very short time.

The aim of research is therefore to find better and faster diagnostic methods for sepsis. One of the scientists researching this field is Doctor Dirk Kuhlmeier from the Fraunhofer Institute for Cell Therapy and Immunology IZI. He explained to which way he and his team are following and what they hope to achieve for the patients sake. How is sepsis currently being diagnosed?

Dirk Kuhlmeier: You use blood cultures to diagnose sepsis. If sepsis is suspected, the guidelines of the German Sepsis Society (Deutsche Sepsis Gesellschaft) recommend taking a blood culture from different parts of the body. The pathogen contained in there is being cultivated in the laboratory to be able to later exactly identify it. As soon as you know what pathogen you are dealing with, you then test in addition whether a potential antibiotic resistance is known. Although the physician generally administers (broadband) antibiotics the minute he/she suspects sepsis – initially you are flying blind, since you cannot always say with absolute certainty whether this is indeed sepsis! And even if you rightly assume sepsis and set up blood cultures, it can take up to 48 hours until a determination is possible. This however is far too late for some patients.

What’s more, especially fungi are difficult to cultivate and in many cases there are even germs that cannot be cultivated – germs that are initially involved in the development of sepsis, but that cannot be detected via a blood culture. These are the kinds of difficulties that have caused us here at the Fraunhofer Institute to search for a faster diagnostic method to detect sepsis, because the risk of patients dying from sepsis increases, the longer the diagnosis or alternatively the determination of the pathogen takes. Which approach are you following?

Kuhlmeier: We rely on methods that don’t involve cultivation steps, but rather biomolecular methods such as PCR, the polymerase chain reaction with which the smallest traces of bacteria or fungi can be detected – against a large background of human DNA. To do this we need a blood sample from the patient to which we add magnetic microparticles which are coated with specific catcher molecules. These are very specific for certain bacteria or fungi. Here we use peptides that don’t just identify a pathogen, but ideally bind a wide spectrum of bacteria and fungi, respectively.

Photo: Young woman with prototype plastic card

Prototype of the lab-on-a-chip, where the magnetic nanoparticles channel the pathogen DNA into the detection chambers; © Fraunhofer IZI, 2011

The peptides thus catch the pathogenic germs which after a short incubation period are being isolated via a magnet and transferred onto a lab-on-a-chip system. The magnetic particles together with the pathogenic germs are led through several functional microchambers.

Specific steps run down in these microchambers that are necessary for the biomolecular analysis such as the PCR for example, which is being carried out on the surface area of the magnetic particles. We have integrated a DNA array with a total of 128 positions on the so-called magneto resistive detection chip. So in theory we can occupy 128 different positions with catcher molecules, so for instance for E. coli or Candida albicans and so on. An electrical resistance measurement then takes place on the chip and finally signals that E. coli for instance was detected – the physician then receives this information.

Photo: Prototype of a reader

After the blood sample has been collected, the card is plugged into a readout unit; © Fraunhofer IZM, 2011 So the physician puts some blood on a card, inserts it into a reader and gets the desired information?

Kuhlmeier: It is our goal to develop a blood sample test tube that is prefixed with magnetic particles, meaning it contains the catcher molecules. You incubate the filled test tube and then attach it to the lab-on-a-chip system, which in turn is being inserted into a reader. In the ideal case scenario you then only push a button and the blood sample testing begins. After approximately 60 minutes – we have set this time window as our goal – the analysis on the card takes place and the user receives a readout with the information on which pathogen he/she is dealing with and which antibiotic resistances exist. That’s our goal – a simple and fast system for everyday life in clinical practice. When will you be able to reach your project goal of having a prototype?

Kuhlmeier: We hope to have developed a prototype by 2013 with which we are able to demonstrate proof of concept. At first we focus here on a specific fungus and gram-positive or -as the case may be- gram-negative bacteria. Certainly the subsequent step in another project then would be to be able to identify as many pathogens as possible that play a role in sepsis with the chip.

The interview was conducted by Simone Ernst and translated by Elena O'Meara.


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