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

Abstract

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. 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. 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. 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.