Abstract: Antimicrobial Photodynamic Therapy (TFDa), which combines a photosensitizing agent (FS), light at an appropriate wavelength and molecular oxygen, has been shown to be effective in inactivating food contaminating microorganisms. The aim of this study was to evaluate the efficacy of FS Safranina (Sf) (300 µg/mL) in reducing the microbial load of cow's milk and Muller Hinton broth (CMH) experimentally contaminated with Staphylococcus aureus (SV1, SV3, SV5) strains. For this, the S. aureus suspensions were added to 24-well plates and subjected to four treatments: Treatment 1: Control (milk/broth); Treatment 2: TFDa (milk/broth + FS (Sf) + green LED lighting (λ=520 nm, light dose of 12.9 J/cm2)); Treatment 3: LED (milk/broth + green LED lighting (λ=520 nm, light dose of 12.9 J/cm2)); Treatment 4: FS (Sf) (milk/broth + FS Sf), in the proportions of 1000 µL milk, 100 µL of bacterial suspension and 100 µL of Sf solution. The plates were stored at 4°C for 48 hours, followed by seeding in Baird Parker agar for microbiological counting. When cultivated in milk and compared to the control treatment, TFDa reduced the S. aureus count by 28.34% (0.72 log CFU/mL) (p<0.05), whereas for the LED and FS treatments there was no a significant difference was observed (p>0.05). When the culture medium was CMH, microbial inactivation ranged from 53.92% (1.17 log CFU/mL) (SV1) to 73.26% (2.74 log CFU/mL) (SV3). For treatments 3 (LED) and 4 (FS), the maximum reduction was 35.94% (SV1) and 73.36% (2.74 log CFU/mL) (SV3). These results indicate that the efficacy of photoinactivation is related to the photodynamic effects caused by the interaction of light with the FS agent, and that the opacity of the medium can influence the FS-microorganism interaction and also the light scattering.