In this study, we established a lactobacillus biotracer system combined with a high-resolution array of culture dishes (20 cm spacing) to quantitatively characterize the three-dimensional spatial distribution of pathogen-laden droplets exhaled during human coughing. Utilizing Lactobacillus bulgaricus as a non-pathogenic surrogate tracer, we systematically analyzed bacterial droplet transmission patterns through a fan-shaped MRS agar dish array in a static closed environment. Our results show that when the mask is not worn, the exhaled droplets exhibit significant segmenting attenuation characteristics: Within the critical distance of 0–1.5 m, large bacterial-containing droplets (>50 μm) exhibited exponential attenuation governed by gravitational sedimentation. Beyond this threshold, droplet nuclei aerosols (<5 μm) transitioned to power-law attenuation dominated by turbulent diffusion. Medical masks demonstrated >90% interception efficiency for short-range transmission (r < 1.5 m), but showed limited suppression of far-field aerosol dispersion, highlighting the necessity for combined N95 respirators and ventilation to achieve multi-level protection. This research innovatively developed a piecewise regression model integrating exponential and power-law attenuation dynamics, providing the first biological evidence for the mechanistic transition between droplet and aerosol transmission. The identified critical distance (rc = 1.5 m) establishes crucial spatial parameters and theoretical foundations for optimizing multi-tiered infection control strategies in healthcare settings.