The use of light as an approach to control the growth of Staphylococcus aureus resistant strains

TOMÁS, ROBERTO SEBASTIÁN; QUIROGA, EZEQUIEL; DI VENOSA, GABRIELA; BUZZOLA, FERNANDA; CASAS, ADRIANA; MAMONE, LEANDRO.

Congreso; LXVI REUNIÓN ANUAL DE LA SOCIEDAD ARGENTINA DE INVESTIGACIÓN CLÍNICA (SAIC); 2021

Photodynamic inactivation (PDI) combines the action of a photosensitizerwith visible light, to cause microorganisms inactivation. The main advantage ofPDI is its effectiveness in bacterial strains resistant to antibiotics. The5-aminolevulinic acid (ALA) is a precursor in endogenous biosynthesis ofporphyrins, some of which have photosensitizing activity. The aim of this work was to employ ALA-based PDI to eliminate planktonicand biofilms cultures of five methicillin-sensitive (MSSA) and six -resistant (MRSA)S. aureus strains.Bacterial viability and porphyrin production were evaluated throughcolony count and fluorescence spectroscopy, respectively. PDI light source wasan array of Tungsten lamps (90 J/cm2). Viability of S. aureus planktoniccultures was reduced around 1-log after ALA-PDI treatment with 1 mM ALA.  As a strategy to increase the outcome of PDI,a more lipophilic derivative of ALA, the hexyl ester ALA (H-ALA), wasused.  H-ALA (1 mM) induced bacterialviability reduction up to 4-logs in all strains tested. The biofilms of RN6390 (MSSA) and ST5-SCCmec I (MRSA, frequentlyinvolved in nosocomial infections) were less sensitive to PDI than theirplanktonic counterparts. In both strains, it was necessary to perform PDI with2 mM ALA or H-ALA to reduce biofilms viability by 0.5 and 0.75 logs,respectively. To improve the effects of PDI on biofilms, we proposed a near-infraredlaser treatment (NIRT) prior to performing PDI. NIRT thermal effects arecapable of inducing changes on biofilm structure. By this strategy, theviability of RN6390 and ST5-SCCmec I biofilms was reduced by 3 and 4-logs,respectively. NIRT induced increase in porphyrin synthesis from ALA or H-ALA aswell as  detachment of bacteria.We conclude that PDI is a promising alternative to eliminate MRSAstrains of sanitary relevance. In addition, we verified the synergistic effectof two radiation-based bactericidal strategies.