The bacterial ecosystem is naturally balanced by viruses known as bacteriophages. Accordingly, they represent an emerging adjuvant to antibiotics to fight bacterial infections. However, the interaction of a single bacterium with bacteriophages remains poorly understood. Here, the use of nanoscale light engineering for the fundamental study of single bacterium-phages interaction is demonstrated. The ability to monitor the lysis of single Escherichia coli cells challenged by two different types of bacteriophages in silicon-on-insulator photonic crystal (PhC) cavities is shown. These nanostructures allow for the optical trapping of a single phage-infected bacterium and their resonant nature allows deciphering the viability of the bacterium by continuously sensing its interaction with the optical field. L3 and H2 PhC cavities are used for the experiments. While the L3 allows for a fine investigation of the bacterial outer membrane, the H2 allows for the optical trapping of the bacterium even after lysis. The analysis of the post-lysis bacterial response provides information that correlates with phage-specific properties. These results, obtained without any need for preliminary labeling nor bioreceptors, deepen the understanding of the fundamentals of bacteria-phages interaction and pave the way to novel breakthrough tools for phage therapy and more generally for antimicrobial susceptibility testing.