The Characteristic And Genes Expression Analysis Of Biofilm Formation In Salmonella Isolated From Beef Processing Plants

Salmonella is carried by beef cattle and easily spread to the environment during beef cattle slaughter and processing through the feces,fur or cross-contamination.Salmonella can form biofilm on the contact surface of meat-processing such as knives,cutting boards and conveyor belt,etc.Biofilm cells are resistants to the regular sterilization strategy,so biofilm formation cause serious cross-contamination and post-processing infectivity with their special structure.Many outbreaks was demonstrated to result from the Salmonella biofilm.From now on,there was many studies on Salmonella biofilm abroad,however,most of them was focused on poultry,seafood,ground meat,clinic or standard strains.Under such a circumstance,the research about the Salmonella biofilm on beef will benefit the study of Salmonella biofilm formation in the factory environment.In this study,a total of 77 strains(76 isolates from slaughtering plants and one ATCC 14028 reference strain from culture collection)of eight serotypes were tested.Biofilm formation capability was assessed by microtitre plate assay under different temperatures(4??10??25??37?and 42?)and pH values(4.5?5.0?5.5?6.0?7.0and 8.0).Then,PCR methods were used for successfully detecting 24 biofilm genes involved in biofilm formation.Finally,the expression of biofilm genes were analyzed by RT-qPCR,and the different condition's(biofilm and planktonic)gene expression at different temperature or pH value were also evaluated.In this study,the main results are as follows:All Salmonella strains produced biofilms on polystyrene micro-well plates at 25?and37?.The ability of Salmonella strains to form biofilms was related to their serotype.S.Senftenberg and S.Kingston produced the most substantial(P<0.05)biofilms.From the result,domestic beef industry had higher risk of Salmonella biofilms.The ability of salmonella produced biofilms on polystyrene micro-well plates was influenced by temperature and pH,and the effect of temperature and pH value were different with different serotypes.The highest quantity of biofilm was formed at 25?or pH 7.0.The least biofilm was formed at 4?independent of pH value.At 10?and 25?,the biofilm-forming ability of Salmonella is increased at acid conditions.It was found that low temperature and acid conditions reduced biofilm formation in beef slaughter and processing.The genes rpoS?fliC?wcaA and invA were detected from all Salmonella.The genes csgB?csgD?csrA?sirA?adr A?gly?fimH?sdiA?ompR?sipB?sipC?luxS and pfs were found in 75%strains and these genes may play a role in the biofilm formation.The detection of igaA had positive correlation(?~2=7.94,P=0.02).The results indicated that the process of biofilm formation were coordinately regulated by several functional genes and other factors.The expression of csgD in planktonic significantly decreased,and the expression of sirA,sdiA and luxS significantly increased with the increasing of culture time.All of the target genes had the highest relative expression in the biofilm at 6d.The expression of functional genes increased first and then decreased or continue to increase with the increase of temperature.The expression of all genes increased first and then decreased with the increase of pH value.Gene rpoS and ompR had a regulatory function to the expression of csgD during biofilm formation.These results indicated that the gene regulation mechanisms of Salmonella biofilm formation were different under different condition or environments.