| Salmonella enterica serovar Enteritidis(SE)is one of major foodborne pathogens,which primarily caused human infection through contaminated chicken and chicken eggs.It is the only bacterium routinely transmitted to humans through intact chicken eggs,and it means that this bacterium must be able to persist inside chicken eggs.In this study,232 SE strains have been screened to differentiate their survival abilities in egg white.The result showed that strain SJTUF 11336 had the highest survival rate,which was isolated from egg dumplings.We also find that higher resistance to egg white exist in these clinical isolates than that in these foodborne isolates,suggested that the obtained stress that clinical isolates came through in the human gastrointestinal tract might enhance the capacity for resistance.Subsequently,we analyzed the gene expression of 5 selected higher resistant strains using RT-qPCR technology,in which egg white resistance related genes in SE were from widely recognized in the previous articles.From our results,not all the selected genes showed an increasing expression in the egg white treated group,which was inconsistent with previous studies.Furthermore,expression level of each gene among different strains showed equivalent diversity.Overall,genes rfbH,rpoS,yafD were proved to have a great influence on the anti-resistance capability of SE,especially the curli fimbriae synthesis gene rpoS,revealed that adhesion plays a very important role for the survival of SE in egg white.However,genes motA,xthA,uspA didn't make sense in this study.In addition,growth characteristics of SE in eggs under different storage conditions were analyzed for the highest resistant strain SJTUF 11336 that adopted in this study,with the relatively sensitive strain ATCC 13076 as a comparison.We analyzed the influence of egg storage conditions by testing the survival rate of the two strains.Based on these results,the dynamic predictive models for the growth of SE in egg white under varying storage conditions were also developed.From this model,it revealed that the two strains displayed similar survival tendency in egg white at different storage conditions,for example,SE strains showed low resistance in eggs stored in high temperature and the survival rate declined first and then ascended along with storing time extending.The survival rate of these two strains reached the minimum value when the storage condition was 37°C for 5 d,which means the antimicrobial activity of egg white at this point was the highest level.The developed dynamic models can provide reliable basis for prediction of SE growth in egg white under varying storage conditions.In conclusion,genes involved in invasiveness,adhesion and LPS biosynthesis played an important role in the molecular mechanism of SE in egg white resistance.The dynamic survival model we have established fully reveals the survival characters of SE during egg storage process,which provides theory basis for prevention and control of SE.Meanwhile,studies on S.Enteritidis resistance to the interaction effect of different bacteriostatic component in egg white,can refer to the survival model to select the appropriate storage conditions,to analyze the specific antimicrobial constituents in egg white and the resistance mechanism of SE. |
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