Rapid-Response Magnetic Enrichment Strategy for Significantly Improving Sensitivity of Multiplex PCR Analysis of Pathogenic Listeria Species

Review of Detection Limits for Various Techniques for Bacterial Detection in Food Samples

Foodborne illnesses can be infectious and dangerous, and most of them are caused by bacteria. Some common food-related bacteria species exist widely in nature and pose a serious threat to both humans and animals; they can cause poisoning, diseases, disabilities and even death. Rapid, reliable and cost-effective methods for bacterial detection are of paramount importance in food safety and environmental monitoring. Polymerase chain reaction (PCR), lateral flow immunochromatographic assay (LFIA) and electrochemical methods have been widely used in food safety and environmental monitoring. In this paper, the recent developments (2013-2023) covering PCR, LFIA and electrochemical methods for various bacterial species (Salmonella, Listeria, Campylobacter, Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli)), considering different food sample types, analytical performances and the reported limit of detection (LOD), are discussed. It was found that the bacteria species and food sample type contributed significantly to the analytical performance and LOD. Detection via LFIA has a higher average LOD (24 CFU/mL) than detection via electrochemical methods (12 CFU/mL) and PCR (6 CFU/mL). Salmonella and E. coli in the Pseudomonadota domain usually have low LODs. LODs are usually lower for detection in fish and eggs. Gold and iron nanoparticles were the most studied in the reported articles for LFIA, and average LODs were 26 CFU/mL and 12 CFU/mL, respectively. The electrochemical method revealed that the average LOD was highest for cyclic voltammetry (CV) at 18 CFU/mL, followed by electrochemical impedance spectroscopy (EIS) at 12 CFU/mL and differential pulse voltammetry (DPV) at 8 CFU/mL. LOD usually decreases when the sample number increases until it remains unchanged. Exponential relations (R2 > 0.95) between LODs of Listeria in milk via LFIA and via the electrochemical method with sample numbers have been obtained. Finally, the review discusses challenges and future perspectives (including the role of nanomaterials/advanced materials) to improve analytical performance for bacterial detection.

Combination of filtration and immunomagnetic separation based on real-time PCR to detect foodborne pathogens in fresh-cut apple

Rapid detection methods require pre-enrichment culture in order to detect low levels of foodborne pathogens. To rapidly detect foodborne pathogens, enrichment culture processes could be replaced. Filtration and immunomagnetic separation methods have been identified to effectively concentrate and separate target pathogens from foods. In this study, a combination of filtration and immunomagnetic separation (IMS) has enabled the rapid and sensitive detection of foodborne pathogens. The pretreatment method, including separation and concentration procedures, increased sensitivity 10-100-fold. The sensitivity of a combination method using filtration and IMS to detect Escherichia coli O157:H7 and Salmonella enterica subsp. enterica serovar Typhimurium was 10⁰-10¹ CFU/10 mL. In fresh-cut apples, IMS combined with filtration effectively improved the detection limit of real-time PCR to 2.70 × 10¹ CFU/g in E. coli O157:H7 and 1.80 × 10² CFU/g in Salmonella. The filtration simplified processing of large-volumes (250 mL) and effectively concentrated pathogens while decreasing immunomagnetic beads used in IMS. Bacterial concentration by IMS combined with filtration increased sensitivity 10-100-fold compared with control. In addition, the application of IMS effectively removed concentrated residual food material (10-15 mg/mL) after filtration, improving relative sensitivity. In conclusion, this method may detect foodborne pathogen in foods such as fresh-cut fruits in a more rapid and sensitive fashion than traditional culture-based methods.

Virulence Characteristics and Distribution of the Pathogen Listeria ivanovii in the Environment and in Food

Listeria ivanovii and L. monocytogenes, are the only pathogenic species of the genus Listeria and share many virulence factors and mechanisms of pathogenicity. L. ivanovii shows host tropism towards small ruminants and rodents and much lower virulence for humans compared to L. monocytogenes. However, severe infections caused by L. ivanovii, resulting in bacteremia, abortion and stillbirth, occasionally occurred in immunocompromised persons and in pregnant women, while in immunocompetent hosts L. ivanovii can cause gastroenteritis. In this review, the updated knowledge on virulence aspects and distribution of L. ivanovii in the environment and in food is summarized. Recent research on its virulence characters at genome level gave indications on how pathogenicity evolved in this bacterial species. As for L. monocytogenes, L. ivanovii infections occurred after the ingestion of contaminated food, so an overview of reports regarding its distribution in food products was carried out to obtain indications on the categories of foods exposed to contamination by L. ivanovii. It was found that a wide variety of food products can be a source of this microorganism and that, like L. monocytogenes, L. ivanovii is able to persist in the food production environment. Studies on its ability to grow in enrichment and isolation media suggested that its occurrence in nature might be underestimated. Moreover, virulence varies among strains for differences in virulence character regulation, presence/absence of genetic regions and the possible instability of a Listeria pathogenicity genomic island, LIPI-2, which is unique to L. ivanovii. We can conclude that L. ivanovii, as a possible pathogen for animals and humans, requires more focused investigations regarding its occurrence in the environment and in food and on intra-species variability of pathogenic potential.