Bacteriophages, i.e. bacterial viruses, are nowadays considered a promising strategy to fight against bacterial infectious diseases (phage therapy). However, their strong species-specificity requires performing so-called phagograms to select the right phage(s) for the right patient based on the lysis capacity of the tested phages on the infecting strain. Meanwhile, it is crucial to decrease as much as possible the time-to-result delay since mortality often depends on the treatment delivery time. We present an optofluidic chip, composed of microfluidic layers embedding silicon photonic crystal resonant cavities, which allows for strong light localization and, thus, the possibility to optically trap objects at powers lower than the damage threshold of biological entities [1]. Since trapping occurs in the near field of the optical resonator, the object's presence, nature and even residual movement within the trap lead to a direct modification of the resonant frequency of the optical cavity. This process allows for the acquisition of information such as the refractive index and the morphology of the trapped object [2]. With this approach, we achieved the trapping and differentiation of several types of living bacteria [3]. We will show the direct observation of bacteria-bacteriophage lytic interaction in an H2 hollow cavity, whose scanning electron microscope (SEM) image and resonant mode near field intensity are depicted in Fig. 1(A-B), respectively. The transmission signal over time collected from a lytic event of a single Escherichia coli B cell infected by Myoviridae T4 bacteriophages is presented in Fig. 1(C). The insets show the state of the bacterium before and after the lysis.