Effect of antibacterial photodynamic therapy on Streptococcus mutans plaque biofilm in vitro

The main objective of this study is to evaluate the antibacterial effect of antibacterial pho-todynamic therapy(aPDT)on Streptococcus mutans(S.mutans)biofilm model in vitro.The selection of photosensitizers is the key step for the efficacy of photodynamic therapy(PDT).However,no studies have been conducted in the oral field to compare the functional char-acteristics and application effects of PDT mediated by various photosensitizers.In this re-search,the antibacterial effect of Methylene blue(MB)/650 nm laser and Hematoporphyrin monomethyl ether(HMME)/532 nm laser on S.mutans biofilm was compared under different energy densities to provide experimental reference for the clinical application of the two PDT.The yield of lactic acid was analyzed by Colony forming unit(CFU)and spectrophotometry,and the complete biofilm activity was measured by Confocal Laser Scanning Microscopy(CLSM)to evaluate the bactericidal effect on each group.Based on the results of CFU,the bacterial colonies formed by 30.4J/cm^(2)532nm MB-aPDT group and 30.4J/cm^(2)532nm HMME-aPDT group were significantly less than those in other groups,and the bacterial colonies in HMME-aPDT group were less than those in HMME-aPDT group.Lactic acid production in all treatment groups except the photosensitizer group was statistically lower than that in the normal saline control group.The activity of bacterial plaque biofilm was significantly decreased in the two groups treated with 30.4 J/cm^(2) aPDT.Therefore,aPDT suitable for energy measurement can kill S.mutans plaque biofilm,and MB-aPDT is better than HMME-aPDT.

Effect of Photoactivated Hypericin on Growth and Antibiotic Susceptibility of Hospital-Related Staphylococcus aureus and Enterococcus sp. Clinical Strains

Resistance against commonly used antibiotics is a serious clinical problem in recent medical practice. There exist several bacterial strains in which the possibilities of their inhibition are very limited due to multidrug resistance. Antimicrobial photodynamic therapy (aPDT) represents an option how to effectively suppress the growth of resistant pathogens. In this work we have studied interactions of potent photosensitizer hypericin (Hyp) with hospital-related gram positive (Gram+) and gram negative (Gram-) bacterial strains and the effects of photodynamic activated Hyp on bacterial susceptibility and/or resistance of these strains to antibiotics. We demonstrated a significant influence of photoactivated Hyp on growth of Staphylococcus aureus and Enterococcus sp. We have also shown that it is extremely important to use the effective concentrations of Hyp for aPDT, which completely inhibit the growth of microorganisms. Otherwise, there appears an increase in resistance, probably due to the activation of efflux mechanisms, which are involved in the efflux of Hyp and antibiotics as well.

Bioresponsive nanotherapy for preventing dental caries by inhibiting multispecies cariogenic biofilms

Early childhood caries(ECC)is a public healthcare concern that greatly reduces the quality of life of young children.As a leading factor of ECC,cariogenic biofilms are composed of acidogenic/aciduric pathogens and extracellular polysaccharides(EPSs),creating an acidic and protected microenvironment.Antimicrobial photodynamic therapy(aPDT)is a noninvasive,painless,and efficient therapeutic approach that is suitable for treating ECC.However,due to the hyperfine structure of cariogenic biofilms,most photosensitizers(PSs)could not access and penetrate deeply in biofilms,which dramatically hamper their efficiency in the clinic.Herein,bioresponsive nanoparticle loaded with chlorin e6(MPP-Ce6)is developed,which largely increases the penetration depth(by over 75%)and retention(by over 100%)of PS in the biofilm compared with free Ce6.Furthermore,MPP-Ce6-mediated aPDT not only kills the bacteria in preformed biofilms but also inhibits multispecies biofilm formation.A rampant caries model is established to mimic ECC in vivo,where the population of cariogenic bacteria is decreased to 10%after MPP-Ce6-mediated aPDT.Importantly,the number and severity of carious lesions are efficiently reduced via Keyes’scoring and micro-CT analysis.This simple but effective strategy can serve as a promising approach for daily oral hygiene in preventing ECC.