Editor: Vera Zarubin
As people swipe up and down on their smartphones, their fingers interact with a conducting polymer that transmits their touch into an electrical signal. Scientists at the Karolinska Institute in Stockholm wondered how bacteria interact with this polymer. If it kills bacteria, it could be used as a new coating for surgical instruments. If it promotes bacterial growth, it has immediate applications in microbial fuel cells and wastewater treatment. It turns out, the polymer can do both, depending on the way you attach the battery.
The polymer in question is PEDOT, which has interested our research group for a long time. It is a conducting polymer that can be modified with a variety of different chemical compounds to enhance different properties. PEDOT has been widely used in smartphone screens and solar cells, but we are interested in using it as an electroactive surface that can “talk” to cells. We have used it in the past to precisely grow epithelial cells in a well-defined gradient. Now, we are turning our attention to infectious bacteria in order to look at new ways of communicating with them to either sense their presence or to stop them from growing.
We were very happy to see that PEDOT prevented the growth of dangerous bacterial colonies called biofilm, especially when we applied a small voltage to reduce the surface. However, the exact composition of the PEDOT surface made no difference at all. As long as the surface was negatively charged, bacteria wouldn’t grow there.
However, to our surprise, when we switched the direction of the electrical current, the opposite happened: more bacteria grew. Bacterial cells were able to grow and thrive on positively charged PEDOT surfaces, irrespective of the composition.
We saw that this was not caused by forces of attraction or repulsion between bacteria and the positively or negatively charged surfaces. Instead, we hypothesized that it was due to the way bacteria interact with the PEDOT itself in order to produce energy. A negatively charged surface is full of electrons, meaning there is no space for bacteria to deposit more electrons, in turn hampering their respiration machinery. Conversely, on a positively charged surface, bacteria can dump spare electrons as fast as they are produced so that they can grow quickly and to high densities.
While the results were interesting, we only used one bacterial genus, Salmonella. In the future, it would be really interesting to test bacteria relevant to medical implant-associated infections such as staphylococci as well as bacteria used in microbial fuel cells such as Shewanella.
This research can lead to the development of a new coating to prevent infections due to biofouling. Imagine surgical instruments or implantable medical devices being coated by the same polymer found in your cell phone. PEDOT can even help produce clean electricity from bacteria found in landfill sites or lakes. If we look a little further ahead, the PEDOT can become a “smart” surfaces in hospitals that detect electrons deposited by bacteria. Then, by selecting the direction of the electrical current, we can choose to either promote or prevent bacterial growth. Why would we want to promote bacterial growth in a hospital? Well, many bacteria go into a dormant state during an infection, causing all essential cellular functions to shut down. This problem arises when we try to treat bacteria, as most antibiotics target active cellular functions such as protein production. No active cells mean antibiotic resistance. If we can use a “smart” surface to wake bacteria up, we may be able to sensitize them to antibiotics and reverse antibiotic resistance.
Research article: Redox-active conducting polymers modulate Salmonella biofilm formation by controlling availability of electron acceptors. npj Biofilms and Microbiomes, 2017.