Antimicrobial resistance poses a significant threat to human health. The resistance arises from factors such as natural bacterial mutations and the widespread misuse of antibiotics in both agronomical and medical practices. Traditional antimicrobial susceptibility testing relies on bacterial growth, resulting in time-consuming processes. To overcome this problem, we introduce a novel approach based on photonic crystal cavities as optical traps and sensors for single bacteria. This method enables real-time monitoring of bacterium-antimicrobial interactions, bypassing the need for bacterial growth. We present experimental results demonstrating the effectiveness of this platform in studying both bacteriophage and antibiotic interactions at the single-bacterium level. Furthermore, our technique offers insights beyond simple susceptibility, including the ability to infer information on burst size for bacteriophages and determine Minimum Inhibitory and Bactericidal Concentrations for antibiotics. Overall, this platform holds promise for revolutionizing antimicrobial susceptibility testing and combating antibiotic resistance.