Taking charge: Using electrochemical impedance spectroscopy to quantify biofilm formation in Pseudomonas spp.

The opportunistic pathogen, Pseudomonas aeruginosa, is infamous for its ability to rapidly form biofilms (<24 h) in inhospitable environments and the development of antimicrobial resistance (AMR). It has been seen to have resistance to nearly all known antibiotics, including last-line antibiotics colistin and carbapenems. AMR is currently considered one of the biggest threats to human health, causing 700,000 deaths annually, expected to rise to 10 million deaths per year by 2050. P. aeruginosa, alongside other opportunistic pathogens, has been implicated in infections following various surgical procedures. Such infections compromise patient recovery and, when a medical implant is present a biofilm can develop that will ultimately require a complex revision surgery to remove the infection.

In this study, impedance spectroscopy and differential pulse voltammetry were carried out in parallel to measure electrochemical and impedance properties of bacteria, allowing for identification and quantification of pyoverdine and pyocyanin; bacterial metabolites. Three Pseudomonas spp. (P. aeruginosa, P. fluorescens and P. putida) were assayed in liquid culture at OD600. The sensor was standardised with pyoverdine and pyocyanin, with an electrochemical reading taken every 30 minutes up to 4 hours. This assay was repeated with Pseudomonas spp. growing in biofilms in LB broth, with a screen-printed electrode as the solid surface. Readings were then used to correlate metabolite production to biofilm production in each Pseudomonas sp. Pyoverdine correlated with biofilm formation for all three assayed Pseudomonas, with variation in the quantity of metabolite produced between species. This allows the two metabolites to be used as indicators of biofilm mass on devices and surfaces.