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Salmonella enterica is a typical foodborne pathogen with multiple toxic effects, including invasiveness, endotoxins, and enterotoxins. Viable but nonculturable (VBNC) is a type of dormant form preserving the vitality of microorganisms, but it cannot be cultured by traditional laboratory techniques. The aim of this study is to develop a propidium monoazide-crossing priming amplification (PMA-CPA) method that can successfully detect S. enterica rapidly with high sensitivity and can identify VBNC cells in food samples. Five primers (4s, 5a, 2a/1s, 2a, and 3a) were specially designed for recognizing the specific invA gene. The specificity of the CPA assay was tested by 20 different bacterial strains, including 2 standard S. enterica and 18 non-S. enterica bacteria strains covering Gram-negative and Gram-positive isolates. Except for the two standard S. enterica ATCC14028 and ATCC29629, all strains showed negative results. Moreover, PMA-CPA can detect the VBNC cells both in pure culture and three types of food samples with significant color change. In conclusion, the PMA-CPA assay was successfully applied on detecting S. enterica in VBNC state from food samples.

Salmonella enterica is a typical foodborne pathogen with multiple toxic effects, including invasiveness, endotoxins, and enterotoxins. Viable but nonculturable (VBNC) is a type of dormant form preserving the vitality of microorganisms, but it cannot be cultured by traditional laboratory techniques. The aim of this study is to develop a propidium monoazide-crossing priming amplification (PMA-CPA) method that can successfully detect S. enterica rapidly with high sensitivity and can identify VBNC cells in food samples. Five primers (4s, 5a, 2a/1s, 2a, and 3a) were specially designed for recognizing the specific invA gene. The specificity of the CPA assay was tested by 20 different bacterial strains, including 2 standard S. enterica and 18 non- S. enterica bacteria strains covering Gram-negative and Gram-positive isolates. Except for the two standard S. enterica ATCC14028 and ATCC29629, all strains showed negative results. Moreover, PMA-CPA can detect the VBNC cells both in pure culture and three types of food samples with significant color change. In conclusion, the PMA-CPA assay was successfully applied on detecting S. enterica in VBNC state from food samples. [ABSTRACT FROM AUTHOR]

Escherichia coli O157:H7 is an important food-borne pathogen and has ability to contaminate food, such as water, meat products, and milk. Moreover, E. coli O157:H7 is the main toxin-producing serotype which can produce Shiga toxin type 1 and type 2 and cause intestinal disease. The strong pathogenicity and lethality of Escherichia coli O157:H7 pose a serious threat to human. This study aims to develop a rapid and visual detection assay of E. coli for rfbE, stx1, and stx2 genes by crossing priming amplification (CPA). The limit of detection of CPA assay for rfbE, stx1, and stx2 genes was 3.20 fg/μl, 320 fg/μl, and 320 fg/μl in genomic DNA, while that of in artificially contaminated food samples was 103 cfu/ml, 105 cfu/ml, and 105 cfu/ml, respectively, which was distinctly higher than that of PCR methods. And the specificity of CPA assay was tested by 22 different bacterial strains and except for E. coli O157:H7 ATCC43895 and other E. coli O157:H7 isolated from eggs, milk, and beef, all strains showed negative results. The visible detection assay was conducted by the addition of calcein in the reaction solutions. The CPA assay showed a successful detection of E. coli O157:H7 (Shiga toxin–producing and non-Shiga toxin–producing) within 60 min under 63 °C with high sensitivity and specificity. These results indicated that the CPA assays with calcein can provide an advanced method to achieve the rapid and visual detection of food-borne E. coli O157:H7. [ABSTRACT FROM AUTHOR]