Electrochemical Sensors for Continuous Monitoring of Bacterial Infections

The Infectious Diseases Society of America recently named six pathogens as the greatest threat to modern day medicine as they currently account for over two thirds of all hospital acquired infections and have the ability to rapidly develop antibiotic resistance. While pharmaceutical companies work to develop new antimicrobial compounds to treat infections, one of the best ways to prevent the emergence of antibiotic resistance, and improve patient outcomes, is early detection followed by fast identification and treatment with targeted antibiotics.

To this end, we are developing electrochemical sensors that will be able to continuously monitor patient wounds for signs of infection. Our detection mechanism uses virulence factors that are excreted by pathogens into their local environment. One such approach measures production of pyocyanin by Pseudomonas aeruginosa, a quorum-sensing molecule that is unique to this species and linked to biofilm formation. As pyocyanin is redox-active, it can be detected electrochemically using standard techniques such as square wave voltammetry (SWV), where the sensitivity of the measurements is limited by the concentration of pyocyanin present in the sample.

Since demonstrating the initial concept, we have focused on improving the sensing system and developing new applications for it within healthcare settings. Here, we will present our recent findings for how it may be possible to improve the sensitivity of the system by coating the electrodes with compounds that cause cells to up-regulate the production of pyocyanin. We have also investigated whether pyocyanin production rates are affected by antibiotic treatment. We will show that a simple electrochemical sensor can be used to provide quantitative information about the efficacy of antibiotic treatment regimes for P. aeruginosa infections. We measured the concentration of pyocyanin surrounding biofilms of P. aeruginosa cells while exposing them to a range of antibiotic concentrations. Figure 1 shows SWVs of Escherichia coli and P. aeruginosa biofilms grown in trypticase soy broth (TSB) for A) 0 hr, B) 12 hr, then exposed to flowing 100 mg/L colistin sulfate TSB after approximately C) 22 hr, D) 35 hr, E) 40 hr, and F) 45 hr. The baseline current for the blank TSB was subtracted from the data shown. SWV performed from -0.5 to 0.2 volts at a frequency of 15 Hz and an amplitude voltage of 50 mV. The E. coli cells do not produce pyocyanin and, therefore, no peak is seen in the current around -0.25 volts. The results show that pyocyanin concentration decreases as cells in the biofilm are killed, and therefore can be used to monitor the effectiveness of treatment.

This work was supported by the U.S. National Science Foundation under Grant #1125535.