Every year, bacterial infections kill millions of people worldwide. That is why the detection of harmful microorganisms is so important – not only in the diagnosis of diseases, but also, for example, in food production. However, the methods available so far are often time-consuming, require expensive equipment, or can only be used by experts. Also, they cannot differentiate between active bacteria and their degradation products.
Instead, the newly developed method detects only intact bacteria. It exploits the fact that microbes attack only certain body cells, which they recognize from the latter's specific sugar molecular structure. This matrix, called the glycocalyx, varies depending on the type of cell. So to speak, it acts as an identifier for body cells. This means that to capture a particular bacterium, we need to know a recognizable structure in the glycocalyx of its preferred host cell, and then use this as a „bait”.
This is precisely what the researchers have done. „In our study, a specific strain of the gut bacterium Escherichia coli – or E. coli for short,” explains Professor Andreas Terford from the Institute of Inorganic and Analytical Chemistry at Goethe University Frankfurt. „We know which cells the pathogen commonly infects. We used this to coat our chip with a synthetic glycocalyx that mimics the surface of these host cells. This way, only bacteria of the targeted E. coli strain adhere to the sensor.”
E. coli has several short arms, called pili, that the bacterium uses to recognize and adhere to its host glycocalyx. „Bacteria use their pili to bind to the sensor in many places, which allows it to hang particularly well,” says Derford. In addition, the chemical structure of synthetic glycocalyx can cause microbes without right hands to slide off it—like eggs from a well-greased frying pan. This ensures that only pathogenic E. coli bacteria are retained.
But how were scientists able to confirm that the bacteria were actually attached to the synthetic glycocalyx? „We bound the sugar molecules to a conductive polymer,” explains Sebastian Palzer, a post-doctoral researcher under Professor Terford and first author of the paper. „By applying an electrical voltage through these 'wires', we can read how many bacteria are bound to the sensor.”
The study documents just how effective it can be: Researchers mixed pathogens from a targeted E. coli strain among harmless E. coli bacteria at various concentrations. „Our sensor was able to detect even very small amounts of harmful microbes,” Derford explains. „What's more, the higher the concentration of the target bacteria, the stronger the signals emitted.”
Paper is the initial proof that the method works. In the next step, the relevant working groups want to examine whether this is a practical test. For example, it is conceivable to use it in areas where there are no sophisticated laboratory diagnostic hospitals.
Publication: Sebastian Palzer, Michael Rohrl, Karina Spormann, Thisbe K. Lindhorst, Andreas Terford: Quantification of bacterial selectivity in composites using glycosylated polypyrrole/hydrogel nanolayers. ACS Applied Materials & Interfaces Article Coming Soon; https://doi.org/10.1021/acsami.3c14387
Download image: https://www.puk.uni-frankfurt.de/151323552?
Caption: By using a customized surface to imbibe targeted pathogens, they separate themselves from a mixture of different bacteria. This makes their detection by electrochemistry easier. Image: Sebastian Palzer, Andreas Terford Research Group, Goethe University Frankfurt
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