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

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

Ciudad Autonoma de Buenos Aires

Congreso; Reunion Conjunta de Biociencias; 2021

SAIC SAI AAFE NANOMED-AR

Photodynamic inactivation (PDI) combines the action of a photosensitizer with visible light,tocause microorganisms inactivation. The main advantage of PDI is its effectiveness in bacterialstrains resistant to antibiotics.The 5-aminolevulinic acid (ALA) is a precursor in endogenousbiosynthesis of porphyrins, some of which have photosensitizingactivity.The aim of this work was to employ ALA-based PDI to eliminate planktonic and biofilmscultures of five methicillin-sensitive (MSSA) and six -resistant (MRSA) S. aureus strains.Bacterial viability and porphyrin production were evaluated through colony count andfluorescence spectroscopy, respectively. PDI light source was an array of Tungsten lamps(90J/cm 2 ).Viability of S. aureus planktonic cultures was reduced around 1-log after ALA-PDI treatmentwith 1 mM ALA. As a strategy to increase the outcome of PDI, a more lipophilic derivative ofALA, the hexyl ester ALA (H-ALA), was used. H-ALA (0.5 mM) induced bacterial viabilityreduction up to 4-logs in all strains tested.The biofilms of RN6390 (MSSA) and ST5-SCCmecI (MRSA, frequently involved in nosocomialinfections) were less sensitive to PDI than their planktonic counterparts. In both strains, it wasnecessary to perform PDI with 2 mM ALA or H-ALA to reduce biofilms viability by 0.5 and 0.75logs, respectively.To improve the effects of PDI on biofilms, we proposed a near-infrared laser treatment (NIRT)prior to performing PDI. NIRT thermal effects are capable ofinducing changes on biofilmstructure. By this strategy, the viability of RN6390 and ST5-SCCmecI biofilms was reduced by 3and 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 MRSA strains of sanitaryrelevance. In addition, we verified the synergistic effect of two radiation-based bactericidalstrategies.