Photodynamic inactivation to prevent and disrupt Staphylococcus aureus biofilm under different media conditions

The goal of this work was to investigate the photodynamic activity of 5,10,15,20-tetrakis[4-(3-N,N-dimethylaminopropoxy)phenyl]chlorin (TAPC) and zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine iodide (ZnPPc⁴⁺ ) as photosensitizers to inactivate Staphylococcus aureus biofilms and prevent their formations in different culture media.

We incubated S aureus biofilms in different culture media: tryptic soy (TS), nutrient (N), Müeller Hinton (MH) broth, TS with glucose 2 and 5% (w/v) with 5 μM ZnPPc⁴⁺ or TAPC and irradiated with visible light (350-800 nm). Photodynamic inactivation (PDI) was determined by count of colony forming units (CFU) and crystal violet method. Furthermore, we studied PDI effect on biofilm development in TS broth. Finally, we examined the effects of PDI on the structure of S aureus biofilm.

Greater inactivation was achieved, using TAPC or ZnPPc⁴⁺ , when S aureus biofilm was grown in N or MH broths rather than in TS. Besides, glucose addition to the medium decreases the ability to develop biofilm and increase the photoinactivation capacity. Prevention of 3 log biofilm developments was obtained when S aureus cultures were treated with TAPC (10 μM) and 108 J/cm² in TS broth and the number of CFU was counted after 24 hours. Moreover, microscopy studies demonstrated modifications in biofilm architecture.

These results indicate that TAPC and ZnPPc⁴⁺ may be promising photosensitizers for photodynamic inactivation of S aureus biofilms or to prevent their formation.