1. Department of Microbiology, School of Biology, College of Science, University of Tehran 2. Department of Microbiology, School of Biology, College of Science, University of Tehran 3. Department of Microbiology, School of Biology, College of Science, University of Tehran
Antimicrobial photodynamic inactivation (apdi) is an encouraging new option for killing pathogenic microorganisms. this method involves the use of a nontoxic photosensitizer, which is excited by exposure to visible light, leading to generate reactive oxygen species. it is likely that during the treatment, the photosensitizer or light would achieve in the target site at sub-lethal concentrations. therefore, microorganisms will not be eradicated completely and may become tolerant to apdi or other antimicrobial agents. the present study was designed to explore the effects of lethal and sub-lethal apdi using methylene blue (mb) on the expression of genes (bsma and bsmb) regulating the biofilm formation and a putative regulatory luxr homologue (swrr) in s. marcescens atcc 13880.
Planktonic cells exposed to lethal and sub-lethal apdi (mb at final concentrations of 0.025 mm and 0.05 mm, respectively, and light dose of 15 j/cm2). treated and untreated cells were allowed to form biofilm for 24 hours. biofilm formation was evaluated using crystal violet (cv) assay and scanning electron microscopy (sem). gene expression of apdi-treated cells were determined by quantitative real-time polymerase chain reaction.
Quantitative assay (cv) results and morphological observations (sem) indicated that both single lethal and sub-lethal apdi treatments resulted in a significant reduction in biofilm formation ability of s. marcescens atcc 13880 compared to their non-treated controls (p<0.05). lethal and sub-lethal apdi down regulated the expression of qs-controlled biofilm formation genes (bsma and bsmb) and qs gene (swrr) in s. marcescens atcc 13880.
Our results indicated that the transcriptional decreases caused by mb mediated lethal and sub-lethal apdi did lead to phenotypic changes. sub-lethal apdi did not result in more biofilm formation ability of bacteria.
Antimicrobial photodynamic inactivation, biofilm formation, quorum sensing, s. marcescens