Antibiotic resistance kills an estimated 700,000 people each year worldwide and experts predict that this number could hit 10 million by 2050. Rapid diagnostics would play an essential role in the fight against this alarming phenomenon by improving the way in which antibiotherapy is used, notably by stopping the unnecessary use of antibiotics. Clinical microbiology has relied on culture as the standard method for characterizing pathogens over the past century. This process is time-consuming and requires large biomasses. In this context, single-cell monitoring would be a significant breakthrough compared to Petri dishes culture. A first step was achieved by the demonstration of single bacterium trapping by optical tweezers and integrated photonics. Here, the nondestructive real-time state monitoring of a single alive trapped bacterium is demonstrated. In order to achieve this, a two-laser setup was developed to simultaneously trap and monitor a single bacterium in the near-field of a nanobeam microcavity. While the first laser is used to excite the optical field tweezing the bacterium, the second laser probes the cavity resonance spectrum. The bacterium optical interaction with the resonant cavity mode allows to assess the bacterium state in real time when subjected to an antibacterial agent (antibiotics, alcohol, temperature). Confronted to standards culture-based methods, this optical label-free approach yields relevant information about bacterial viability, without time-consuming culture or staining. Those results evidence that on-chip devices operating at telecom wavelength may greatly enhance the monitoring of bacteria in the near future leading to major improvements in health care diagnosis and patient treatments.