The effect of antimicrobial photodynamic therapy on the expression of biofilm associated genes in Staphylococcus aureus strains isolated from wound infections in burn patients

Purpose: Burn patients are particularly susceptible to microbial infection. Staphylococcus aureus causes burn wound, impetigo and cellulitis. Although sub-lethal antimicrobial photodynamic therapy (aPDT) would not result in microorganism killing, it can considerably influence microbial virulence factor. Methods: Twelve methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA) isolated from burns patients. To determine the sub-lethal dose of aPDT, 12 clinical isolates of S. aureus photosensitized with 100 μg ml -1 toluidine blue O (TBO) and irradiated by light emitting diode (LED) with a wavelength of 630 ± 10 nm and energy densities of 52.0, 104.1, and 156.2 J/cm2, then bacterial viability was measured. The effects of sub-lethal aPDT on the expression levels of ica ABCD and ica R genes were assessed by quantitative Real-time PCR (qRT-PCR) method. Result: Fifty and 100 μg ml-1 of TBO significantly reduced the mean cell survival in the MRSA (2.5 - 3 log10) and MSSA (2.75-3.1 log10) isolates. The average expression levels of icaA, ica B, ica C, and ica D in the MRSA and MSSA isolates were decreased by (12, 14, 11, and 9) and (13, 14.5, 12, and 9.5) fold change, respectively (P < 0.05). However, the expression of ica R gene was decreased by 6 and 8 folds change in MRSA and MSSA, respectively. Conclusion: The potential of TBO-mediated aPDT could reduce the expression of ica ABCD as important genes involved in biofilm formation and ica R gene as a repressor of the ica operon. Therefore, the use of aPDT agents as a complementary therapy in wound infections of burn patients is recommended.