Comparative Study Of The Effects Of MB-PDT And HMME-PDT On Streptococcus Mutans Plaque Biofilm

Objective:This study investigated two photosensitizers,methylene blue(MB)and hematoporphyrin monomethyl Ether(HMME),and their photodynamic Therapy(PDT)at two energy densities.The bactericidal effect of Streptococcus mutans(S.mutans)biofilm cultured in vitro.The effects of two photosensitizers and their respective mediated PDT therapy on acid production and metabolic capacity of Streptococcus mutans biofilm were examined.The biofilm image of the transformed Streptococcus mutans was observed using a laser confocal microscope to determine the bacterial activity in the biofilm.Methods:1.Plate colony count:A model of Streptococcus mutans biofilm was cultured on a hydroxyapatite(HA)disk and divided into 8 groups.After each group of treatments were completed,they were diluted stepwise and counted by plate colony counting.2.Determination of acid production capacity:Each group of the treated samples was further cultured for 3 hours,and the concentration of L-lactic acid was measured by an enzyme spectrophotometry using a lactic acid detection kit.3.Laser confocal image observation:The samples of each group were stained.Three samples were selected from each group and placed under laser confocal microscopy to collect and process image information.The number of live bacteria(green signal intensity)and the number of dead bacteria(red signal intensity)were collected and calculate the ratio.Results:1.Plate colony count display:Compared with the saline control group,all PDT treatment groups(groups 2,3,5,and 6)showed a decrease in the number of colonies,and the difference was statistically significant(p<0.05).In the PDT group,the sterilization effect of the30.4J/cm~2 PDT group was better than that of the 15.2J/cm~2 PDT group,the difference was statistically significant(p<0.05).Compared with the different photosensitizers,the MB-PDT group had better sterilization effect than the HMME-PDT group.2.L-lactic acid concentration test results:Compared with the saline control group,all PDT treatment groups showed a decrease in L-lactic acid concentration,and the difference was statistically significant(p<0.05).3.Laser confocal image processing results:Laser confocal image analysis showed that compared with the saline control group,all PDT treatment groups showed a decrease in the proportion of live bacteria,and the difference was statistically significant(p<0.05).Conclusion:Under the conditions of this study,it can be concluded that PDT therapy with different photosensitizers and energy density has a sterilizing effect on Streptococcus mutans in plaque biofilm,and the sterilization effect of MB-PDT is better than HMME-PDT.All PDT treatments reduce the acidogenic capacity of Streptococcus mutans plaque biofilm.PDT treatment reduced the proportion of viable bacteria in the plaque biofilm,and the proportion of viable bacteria in the high energy density group was lower than that in the low energy density group.