PCR Detection And Bacteriophage-based Biocontrol Of Salmonella Spp In Meat Products

Salmonella is one of the important foodborne bacteria contaminating meat products.In this study,we investigated the Salmonella contamination and its controlling method in meat products.The first objective of this study was to detect and evaluate the contamination rate of Salmonella in packaged and unpackaged meat products from retail stores in Yangzhou.The detection of Salmonella in beef was performed via pre-enrichment followed by serotyping and analysis utilizing traditional cultural method and PCR.This study revealed that retail raw meats were contaminated with Salmonella.Out of 100 samples,26%and 29%were found contaminated based on standard culture method and PCR,respectively.The most prevalent serotypes in retail beef samples were Salmonella Kentucky(5),Salmonella Typhimurium(4),Salmonella Thompson(3),Salmonella Haardt(3)and Salmonella Veyle(3).Serotypes were analyzed in higher concentration and variability in unpackaged samples.Our study successfully applied PCR method for the detection of Salmonella in naturally contaminated retail beef samples within a much shorter time than the standard culture method.The specificity and sensitivity was comparable to the currently used standard culture method.The PCR method could be used in the future to quantify initial-target DNA in retail beef samples both fresh and processed.The developed PCR method has the potential to be of benefit in routine food testing to rapidly release products shown to be negative by the real-time PCR method.The second aim was to develop a bacteriophage-based strategy for the control of S.enteritidis in mixed-ingredient salads containing meat.SapYZU01previously isolated from a soil sample,is a novel lytic phage having potential to lyse S.enteritidis.This phage exhibited characteristics of growth-inhibition and had no virulence or antibiotic resistance genes,while genes encoding holin,lysin,i-spanin,o-spanin,and HNH endonucleases in phage genome.SapYZU01 significantly decreased the viability of S.enteritidis cells in various food matrices.SapYZU01(multiplicity of infection(MOI)-100)decreased the counts of S.enteritidis cells in lettuce and chicken samples by 1.21 log CFU/g within 18 h at 25℃ and by 4.3 log CFU/g within 24 h at 37℃.Notably,bacterial counts in the salad were decreased markedly(by 4.0 log CFU/g)upon treatment of contaminated lettuce with SapYZU01(108 PFU/mL)prior to salad preparation.Bacterial counts were decreased by 3.8 log CFU/g in salads prepared with contaminated lettuce and sterilized chicken meat.In contrast,treating sterilized chicken meat with SapYZU01(108 PFU/mL)before mixing it with contaminated lettuce decreased the bacterial count of the salad by 1.2 log CFU/g at 25℃.The growth-inhibiting activity of SapYZU01 against S.enteritidis was not significantly different between the groups treated with 106 and 108 PFU/mL of the phage.These findings indicate the potential application of SapYZU01 as a natural biocontrol agent against S.enteritidis in mixed-ingredient salads.