Formation Characteristics Of Salmonella Typhimurium Biofilm And The Bactericidal Effect Of Photodynamic Technology

Salmonella is one of the four big common foodborne pathogens,which has a wide range of serotypes and is widely distributed.The annual food poisoning incident due to Salmonella ranks the top of bacterial borne cases.Salmonella typhimurium,Salmonella enteritis and Salmonella cholerae are the most common pathogens causing food safety crisis.Salmonella typhimurium,the non-host adaptive serotype,can be pathogenic to many hosts,produce endotoxin and enterotoxin,cause diarrhea,vomit and fever,and threaten human health seriously.In this study,turbidimetry and plate colony counting were used to investigate the effect of culture conditions on the biofilm(BF)formation characteristics of Salmonella typhimurium and its tolerance to environmental lethal stress.The inactivation and its mechanism of curcumin mediated photosensitization on Salmonella typhimurium was studied by agarose gel electrophoresis,real time-polymerase chain reaction(RT-PCR),sodium dodecyl polyacrylamide gel electrophoresis sulfate(SDS-PAGE),confocal laser scanning microscopy(CLSM)and scanning electron microscopy(SEM),and the bactericidal application of photodynamic technology on Salmonella typhimurium in different types of milk powder was conducted.The main results are as follows:The growth characteristics and the structure change of Salmonella typhimurium biolifm on the surface of the glass were clearly investigated by the crystal violet stain.Effect of ethanol activity on the formation of Salmonella typhimurium biofilm and effect of ethanol adaptation on tolerance to lethal stress of planktonic and biofilm were investigated.Ethanol added at different level during 48 h incubation of Salmonella typhimurium inhibited the formation of biofilm significantly,however,ethanol added after the incubation of Salmonella typhimurium for 24 h at 5%level only promoted the growth of biofilm.Ethanol at level of 5%increased the tolerance of bacteria to malic acid in biofilm formation under the condition of 1/10 tryptone soy broth.In addition,5%ethanol adaptation increased planktonic resistance to 12%ethanol and 5 mg/m L malic acid.Curcumin mediated photodynamic technology had a significant bactericidal effect on Salmonella typhimurium and its biofilm.Different curcumin concentration and illumination time were selected to explore the optimal inactivation condition of photodynamic technology,the bactericidal effect of photodynamic technology was observed by confocal laser scanning microscopy and scanning electron microscopy.Curcumin(80?M)combined with blue light(200 mw/cm~2)irradiation for 30 min had the inactivation rate of 99%for Salmonella typhimurium biofilm.The entire field of vision of the confocal laser spectrum was nearly red after irradiation,and the bacteria observed by SEM was wrinkled and irregular,indicating that most of the bacteria died.Agarose gel electrophoresis,real-time fluorescence quantitative PCR and SDS-PAGE showed that photodynamic technology caused damage to DNA and proteins of Salmonella typhimurium.Curcumin mediated photodynamic technology had an obvious bactericidal effect on Salmonella typhimurium in three kinds of milk powder.The bactericidal effect of photodynamic technology on Salmonella typhimurium in infant formula milk powder was obviously weaker than that of whole milk powder and skim milk powder,and the bactericidal effect was related to the irradiation liquid level,curcumin concentration and milk concentration.Irradiation liquid level(0.2 cm),curcumin(120?M)and milk concentration(10 times dilution)achieved the best bactericidal effect.The results showed that curcumin mediated photodynamic technology could effectively control the contamination of Salmonella typhimurium and its biofilm by damaging DNA,protein,cell membrane and morphological structure of bacteria,and it could be applied in food industry,especially in dairy products frequently contaminated by Salmonella typhimurium.