Abstract
Antimicrobial resistance (AMR) describes the ability of bacteria to become immune to antimicrobial treatments. Current testing for AMR is based on culturing methods that are very slow because they assess the average response of billions of bacteria. In principle, if tests were available that could assess the response of individual bacteria, they could be much faster. Here, we propose an electro-photonic approach for the analysis and the monitoring of susceptibility at the single-bacterium level. Our method employs optical tweezers based on photonic crystal cavities for the trapping of individual bacteria. While the bacteria are trapped, antibiotics can be added to the medium and the corresponding changes in the optical properties and motility of the bacteria be monitored via changes of the resonance wavelength and transmission. Furthermore, the proposed assay is able to monitor the impedance of the medium surrounding the bacterium, which allows us to record changes in metabolic rate in response to the antibiotic challenge. For example, our simulations predict a variation in measurable electrical current of up to 40% between dead and live bacteria. The proposed platform is the first, to our knowledge, that allows the parallel study of both the optical and the electrical response of individual bacteria to antibiotic challenge. Our platform opens up new lines of enquiry for monitoring the response of bacteria and it could lead the way towards the dissemination of a new generation of antibiogram study, which is relevant for the development of a point-of-care AMR diagnostics.
Highlights
The major cause for the increase of bacterial infections is their ability to resist antimicrobial treatments [1], termed antimicrobial resistance (AMR)
The bacterium is probed by an AC field, which allows us to pick up changes in the impedance when it is challenged by an antibiotic
We have introduced the novel concept of a multiparameter, electro-photonic platform that allows monitoring the response of bacteria to antibiotic challenge
Summary
The major cause for the increase of bacterial infections is their ability to resist antimicrobial treatments [1], termed antimicrobial resistance (AMR). Electrochemical Impedance Spectroscopy (EIS) with configurations based on interdigitated microelectrodes has demonstrated the lowest detection limit down to 10 CFU/mL [15,16] and a clear change in impedance has been observed when exposing bacteria to antibiotics [17]. These examples indicate the suitability of electrical techniques for the study of bacterial infections, they typically operate at the bacterial community level and require cell growth with concentrations in the 105-106 CFU/mL range [18] to obtain a detectable change of impedance. By realizing the cavities in doped silicon with interdigitated contacts, we predict a variation in measurable electrical current by up to 40% between live and dead bacteria, thereby facilitating the assessment of bacterial metabolism via impedance measurements
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