Electrical cell-substrate impedance sensing (ECIS) as a tool to study microbial-cell interactions.

ECIS is an impedance-based method to study the cellular responses to a stimulus. Manipulating the alternating current frequencies in ECIS helped reveal the adherent monolayer properties, including morphology, spreading, proliferation, changes in junctional proteins and barrier integrity. Our objective in the current study was to understand the progression of Pseudomonas infection in the airway epithelial cells using ECIS. The study also aimed at understanding the feasibility of using ECIS to study drug interactions on monolayer barrier functions. A significant reduction in impedance was noted in response to Pseudomonas infection, indicating loss of morphology and cell viability. At frequencies lower than 2000 Hz, a gradual decrease in impedance was observed during the early phase of infection, indicating a loss of junctional integrity. On the other hand, at frequencies above 16,000 Hz, a reduction in impedance was observed only during the later phases of infection. This suggested that Pseudomonas reduced the barrier integrity of cells during the early phase to gain access into the cells. Changes in cell morphology and subsequent loss of cell viability occur during the later phases of infection. Azithromycin is known to increase the barrier integrity of the monolayer (by increasing the expression of junctional proteins). We observed that pretreatment of A549 monolayers with azithromycin inhibited the progression of infection by Pseudomonas ATCC 27853 and delayed the infection of the epithelium by S373 clinical isolate. Our study is the report on the mechanism of bacterial infection progression using ECIS. It can be observed that an improvement in the barrier integrity reduces the susceptibility to bacterial infections. ECIS was demonstrated to be an effective tool for studying microbial-cell interactions and the role of drug molecules.