Rapid Quantification of Pathogenic SalmonellaTyphimurium and Total Bacteria in Eggs

Rapid quantification of pathogenic Salmonella Typhimurium (S. typhimurium) and total bacteria in eggs is highly desired for food safety control. However, the complexity of the egg matrix presents a significant challenge for sensitive detection of bacteria. In this study, a sample pretreatment protocol, including dilution, fat dissolution, protein degradation, filtration, and washing, was developed to circumvent this challenge. The Flow NanoAnalyzer was employed to analyze individual bacteria with nucleic acid and immunofluorescent staining. Eggs spiked with pathogenic S. typhimurium and harmless Escherichia coli K12 (E. coli K12) were used as the model system to optimize the sample pretreatment protocol. S. typhimurium and total bacteria in eggs can be quantified without cultural enrichment, and the whole process of sample pretreatment, staining, and instrument analysis can be accomplished within 1.5 hours. The as-developed approach can specifically distinguish S. typhimurium from other bacteria, and successful application to bacterial detection in eggs freshly purchased from supermarkets and spoiled eggs upon inappropriate storage was demonstrated.

The bacterial recovery rate upon sample pretreatment, detection limit, and dynamic range for S. typhimurium in eggs were 92%, 2 × 10³ cells/mL, and from 2 × 10³ to 4 × 10⁸ cells/mL, respectively.

Talanta, 2020, 217, 121020.