Acid Tolerance Of Salmonella Isolated From Pigs And Cross Protection For Salt,High Temperature,and Oxidative Stress

Objective:Salmonella is the most common pathogen of zoonotic food borne disease.Moreover,it is the most likely pathogens cause of food poisoning and lead to about 40%of food poisoning incidents in China.Acid,often used as food additives,preservatives,feed acidifier and other ingredients,with the use of acids more and more widely,the bacteria then produced acid tolerance(ATR)in order to adapt to the adverse effects of acid stress.Therefore,pollution status of Salmonella in pork industry chain of Fujian Province was investigated and then,the acid tolerance of isolated Salmonella was detected,meanwhile the phenotype and genotype of acid tolerance as well as the cross protection character of Salmonella was detected too.Method:A total of 1067 samples from each stage of the pork industry chain were collected for isolation and identification of Salmonella.The isolation and identification methods of Salmonella were optimized.A Salmonella viability count method and an acid tolerance model were established to carry out the induction of acid tolerance in Salmonella,and screening of Acid-resistant strains from the clinical strains.The expression of acid tolerance genes and their associated proteins,as well as the cross-protection characteristics of acid-tolerant bacteria were studied using fluorescence quantitative PCR and Western blotting.Results:162 strains of Salmonella were isolated from pork industry chain of Fujian Province.Eight of 162 clinical Salmonella strains had acid tolerance to pH 4.0 or lower.These acid-resistance strains may be correlated with the pollution of slaughter.These strains were found to express the transient tolerance pathways of the fur gene during the logarithmic growth phase.Meanwhile,in the stationary phase acid resistance was associated with pathways associated with the ompR gene.Protein detection showed that the expression levels of Fur,RpoS,ClpP,and N1pD proteins corresponded with gene expression.Most of the clinically isolated acid-tolerant bacteria also were highly salt tolerant;meanwhile,only some were tolerant of oxidative stress,and there was no evidence of increased temperature tolerance.Standard bacteria of Salmonella Enteritidis was induced to acid tolerance,the results of its acid tolerance gene test showed that the relative expression of the Salmonella Enteritidis in logarithmic growth phase acid resistance related fur gene increased significantly.At the same time,after acid induction,Fur,ClpP,NlpD protein expression levels also increased to varying degrees.There was correlation between rpoS gene expression and induction pH value.The acid tolerance of Salmonella enteritidis was not associated with the induced acid strength and pH.In this study,the relative expression of cross-protection related genes of Salmonella enteritidis was significantly increased under all induction conditions.Conclusions:We conclude that the acid-tolerance of strains in the pork industry is related to the fur and ompR genes,and acid-tolerance is associated with salt-tolerance.Salmonella enteritidis and Salmonella typhimurium have different acid resistance mechanisms.Acidostasis of Salmonella enteritis is associated with salt tolerance,heat tolerance,and antioxidant stress.