Photodynamic Inactivation Of Food-borne Pathogenic Bacteria By Hematoporphyrin Methyl Ether

Photodynamic therapy of hematoporyrin methyl ether(HMME) has a frequent clinical application and shows a satisfactory clinical effect,however the photodynamic inactivation of HMME in the antibiotic research has seldom been reported.The photodynamic inactivation of Gram-positive bacteria Staphylococcus aureus(S.aureus),Bacillus cereus,Bacillus spores and Gram-negative bacteria Escherichia coli(E.coli) by HMME were investegated through the reduction of colony form unit(CFU),atomic force microscopy(AFM) and fluoroscopic images.1 HMME has the absorption peak of 392 nm,the fluoroscence excitation peak of 398 nm, and the red fluorescence emission peak of 615 nm.2 S.aureus and Bacillus cereus were effectively photoinactivated with the concentration of 25μg/ml by 99.9%killing effects,however,little killing effect were obtained at the above same concentration of HMME to E.coli and Bacillus spores.When the concentration of HMME was increased to 150μg/ml,its photodynamic inactivation were found,with the killing effcts of 99.9%and 55.5%to E.coli and Bacillus spores respectively.3 Under the AFM images,the photodynamic inactivated bacteria S.aureus showed the damage of cell membrane and the leakage of the cell contents from the cell.However,little photomorphology changes were observed under AFM for the non-inactivated bacterial cells,E. coli and Bacillus spores.The result indicated that the killing effect of HMME was through destruction of bacteria cells.4 The fluoroscopic images showed that the higher concentration of the HMME was,the more Bacillus spores released flurescence,and the more clearer the images were,indicating that the HMME entered in to the spores and led to damage to the internal structrue of spore.In conclusion,the Gram-positive bacteria can be effectively photoinactivated by low concetration of HMME,wheres Gram-negative bacteria and the spore of bacteria were not susceptible to photosensitized destruction with similar low concetration of HMME.HMME is an effective photodynamic inactivation agent to Gram-positive bacteria,however,an appropriate way to break though and damage the cell wall,and help the HMME enter into the cell is further studied for the application of photodynamic technogy to Gram-negative bacteria.