Abstract
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.
Highlights
During food processing, food is frequently contaminated by foodborne bacteria, including Staphylococcus aureus, Salmonella enterica, and Escherichia coli O157 (Kirk et al, 2015; Miao et al, 2017a; Sharma et al, 2019)
Two standard S. enterica ATCC14028 and ATCC29629 were used as positive controls
Viable but nonculturable (VBNC) state occurs during the chlorination of wastewater or food (Oliver et al, 2005; Zeng et al, 2013)
Summary
Food is frequently contaminated by foodborne bacteria, including Staphylococcus aureus, Salmonella enterica, and Escherichia coli O157 (Kirk et al, 2015; Miao et al, 2017a; Sharma et al, 2019). Various serotypes of Salmonella are implicated in foodborne infections and contaminate food products, including eggs, milk, poultry, meat, and vegetables. It is the main cause of human gastrointestinal and other related diseases (Bao et al, 2017a,b; Wen et al, 2020). Studies confirmed that S. enterica is capable of entering into the viable but non-culturable state (VBNC) state under an adverse environment, which could include low-temperature, salt stress, and nutrient starvation VBNC cells cannot be detected by traditional culture-based methods (Xu et al, 2011a; Lin et al, 2017; Miao et al, 2017a; Xie et al, 2017a). It is urgent to develop a rapid and sensitive assay to detect S. enterica, especially in the VBNC state
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