Real-time label-free exploration of the dynamics and interactions of bacteriophages

Bacteriophages are the focus of extensive research and monitoring their dynamics and interactions with bacterial hosts is crucial to characterise the mechanisms of infection and support potential applications in biotechnology and medicine. Traditional monitoring techniques rely on the fluorescent labelling of bacteriophages due to their size being nanometric. In this paper, we propose a novel, label-free method to generate optical signatures of bacteriophages in a conventional microscopy setup by exploiting the optical phenomenon of caustics. We utilised previously isolated Pseudomonas aeruginosa phage (pelp20 and phiKZ) and a novel Escherichia coli phage (EcoLiv25) to demonstrate detection and tracking within liquid laboratory media. The results obtained confirm the feasibility of visualising and monitoring over time a diverse array of bacteriophages, offering a simpler and less invasive means of observation for research and application in microbiology and related fields.