Direct Detection of Escherichia coli, Staphylococcus aureus, and Salmonella spp. in Animal-derived Foods Using a Magnetic Bead-based Immunoassay

Preparation of polyclonal antibody against a universal bacterial antigen OmpA deduced by bioinformatic analysis and preliminary evaluation of concentration effects on foodborne pathogens

Rapid and ultrasensitive microbial detection in actual samples have challenges because of target pathogen diversity and low abundance. In this study, we attempted to capture and concentrate multiple pathogens by combining magnetic beads with polyclonal antibodies against a universal antigen of ompA, LAMOA-1, before further detection. A protein sequence consisting of 241 amino acids with spatial conformation similar to E. coli ompA was identified and expressed as a recombinant protein in prokaryotes according to the results of sequence alignment among 432 sequences of ompA belonging to intestinal bacteria from gram-negative bacteria. Purified from immunized rabbits, the anti-LAMOA-1 antibody was shown to effectively recognize 12 foodborne bacterial species. Antibody-conjugated beads were used to concentrate the bacteria when the bacterial concentration in artificially contaminated samples is between 10 and 100 CFU/mL, which shortens detection duration by 8-24 h. The enrichment strategy is potentially beneficial for detection of foodborne pathogens.

Assessment of Foodborne Bacterial Pathogens in Buffalo Raw Milk Using Polymerase Chain Reaction Based Assay

Milk is a putrescible commodity that is extremely prone to microbial contamination. Primarily, milk and dairy products are believed to be easily contaminated by pathogenic microorganisms, including Listeria monocytogenes, Salmonella spp., and Staphylococcus aureus. The microbiological quality of raw milk and dairy products regarding foodborne pathogens is of paramount importance due to concern of human health. In this study 400 buffalo raw milk samples were screened for assessing the prevalence of L. monocytogenes, Salmonella spp., and S. aureus. This study implemented uniplex-polymerase chain reaction (u-PCR) and multiplex-polymerase chain reaction (m-PCR) assays for the fast simultaneous detection of these pathogens comparing to the conventional culturing methods. Raw milk samples were found contaminated with the prevalence of 2.2%, 4.0%, and 14.2% for L. monocytogenes, Salmonella spp., and S. aureus, respectively. These pathogens were detected with the optimized polymerase chain reaction assays after 6 h of enrichment. u-PCR and m-PCR demonstrated the limit of detection as 10⁴, 10², and 10 cells/mL after 6, 12, 18, and 24 h for each culture of the pathogens. A high sensitivity (10 colony-forming unit [CFU]/mL) of the m-PCR protocol was noted. The developed protocol is a cost-effective and rapid method for the simultaneous detection of pathogens associated with raw milk and dairy industries.

Advances in magnetic nanoparticles for the separation of foodborne pathogens: Recognition, separation strategy, and application

Foodborne pathogens contamination is one of the main sources of food safety problems. Although the existing detection methods have been developed for a long time, the complexity of food samples is still the main factor affecting the detection time and sensitivity, and the rapid separation and enrichment of pathogens is still an objective to be studied. Magnetic separation strategy based on magnetic nanoparticles (MNPs) is considered to be an effective tool for rapid separation and enrichment of foodborne pathogens in food. Therefore, this study comprehensively reviews the development of MNPs in the separation of foodborne pathogens over the past decade. First, various biorecognition reagents for identification of foodborne pathogens and their modifications on the surface of MNPs are introduced. Then, the factors affecting the separation of foodborne pathogens, including the size of MNPs, modification methods, separation strategies and separation forms are discussed. Finally, the application of MNPs in integrated detection methods is reviewed. Moreover, current challenges and prospects of MNPs for the analysis of foodborne pathogens are discussed. Further research should focus on the design of multifunctional MNPs, the processing of large-scale samples, the simultaneous analysis of multiple targets, and the development of all-in-one small analytical device with separation and detection.

Giant Magnetoresistance Biosensors for Food Safety Applications

Nowadays, the increasing number of foodborne disease outbreaks around the globe has aroused the wide attention of the food industry and regulators. During food production, processing, storage, and transportation, microorganisms may grow and secrete toxins as well as other harmful substances. These kinds of food contamination from microbiological and chemical sources can seriously endanger human health. The traditional detection methods such as cell culture and colony counting cannot meet the requirements of rapid detection due to some intrinsic shortcomings, such as being time-consuming, laborious, and requiring expensive instrumentation or a central laboratory. In the past decade, efforts have been made to develop rapid, sensitive, and easy-to-use detection platforms for on-site food safety regulation. Herein, we review one type of promising biosensing platform that may revolutionize the current food surveillance approaches, the giant magnetoresistance (GMR) biosensors. Benefiting from the advances of nanotechnology, hundreds to thousands of GMR biosensors can be integrated into a fingernail-sized area, allowing the higher throughput screening of food samples at a lower cost. In addition, combined with on-chip microfluidic channels and filtration function, this type of GMR biosensing system can be fully automatic, and less operator training is required. Furthermore, the compact-sized GMR biosensor platforms could be further extended to related food contamination and the field screening of other pathogen targets.

Sandwich capture ultrasensitive sensor based on biohybrid interface for the detection of Cronobacter sakazakii

A simple, rapid and ultrasensitive visual sensing method for the detection of Cronobacter sakazakii (C. sakazakii) based on a biohybrid interface was established. During the entire sensing process, quadruple-cascade amplification showed its superior sensing performance. First, the prepared immunomagnetic beads (IMB) were used to isolate and enrich specific targets from the food matrix. After adding the fusion aptamer, the aptamer sequence specifically recognized the target and formed the immune sandwich structure of antibody-target-fusion aptamer. In addition, the fusion aptamer also included the template sequence of exponential amplification reaction (EXPAR), which contained the antisense sequence of the G-rich sequence. Therefore, a large number of G-rich sequences can be generated after EXPAR can be triggered in the presence of Bst. DNA polymerase, nicking endonuclease, cDNA, and dNTP. They were self-assembled into G-quadruplex structures and then combined with hemin to form G4/hemin DNAzyme, resulting in visible coloration and measuring absorbance at 450 nm for quantitative detection. The assay showed a limit of detection (LOD) of 2 CFU/mL in pure culture and 12 CFU/g in milk powder in optimal conditions. This method provides a promising strategy for rapid and point-of-care testing (POCT) since it does not require DNA extraction, medium culturing, and expensive instrumentation. KEY POINTS: •Single-cell level detection of C. sakazakii with ultrasensitive and rapidness •The fusion aptamer integrated recognition and amplification •Sensing analysis of C. sakazakii based on cascade amplification of biohybrid interface.

Active Bionanocomposite Coating Quality Assessments of Some Cucumber Properties with Some Diverse Applications during Storage Condition by Chitosan, Nano Titanium Oxide Crystals, and Sodium Tripolyphosphate

Cucumbers have a short shelf-life of about 14 days, they are perishable due to the high moisture content. This study aimed to study the effects of nano-coating material such as titanium nanoparticles and chitosan with the addition of sodium tripolyphosphate as a crosslinker to enhance cucumber quality during storage. Some essential physical, chemical, and biological parameters were determined. CH-Nano-ST (chitosan/nano titanium oxide crystals/sodium tripolyphosphate) retained the maximum greenness, −7.99, compared to CH-Nano samples, which recorded −7.31. CH-Nano (chitosan/nano titanium oxide crystals) remained the lightest, 44.38, and CH-Nano-ST was a little darker (43.73) compared to the others treatments. The discoloration was extra severe with control (22.30), which started to spoil after the end of the first week. After 21 days of the storage period at 10 °C, the reducing sugars content reduced to reach −0.64 g/100 g and −0.21 g/100 g for CH-Nano and CH-Nano-ST treatments, respectively. The CH-Nano-ST treatment presented a lower value of toughness, followed by CH-Nano at the end of the storage period. Moreover, the highest crispness index was detected for CH-Nano (5.12%), while CH-Nano-ST treatment had a slight decline to reach 4.92%. The biological results indicated that CH-Nano-ST treatment can be applied to delay the microbial contamination of Salmonella spp. in cucumbers as it reached 0.94 log CFU/g, while the CH-Nano treatment reached 1.09 log CFU/g, at the end of the storage period. In summary, nano-coating treatments with the addition of sodium tripolyphosphate can be applied to regulator postharvest quality measurements of the biological activities in cucumbers during storage at 10 °C until 21 days.

A detection method of Escherichia coli O157:H7 based on immunomagnetic separation and aptamers-gold nanoparticle probe quenching Rhodamine B's fluorescence: Escherichia coli O157:H7 detection method based on IMS and Apt-AuNPs probe quenching Rho B' s fluorescence

This research aimed to detect Escherichia coli O157:H7 in milk based on immunomagnetic probe separation technology and quenching effect of gold nanoparticles to Rhodamine B. Streptavidin-modified magnetic beads (MBs) were combined with biotin-modified antibodies to capture E. coli O157:H7 specifically. Gold nanoparticle (AuNPs) was incubated with sulfhydryl-modified aptamers (SH-Aptamers) to obtain the Aptamers-AuNPs probe. After magnetic beads captured target bacteria and formed a sandwich structure with the gold nanoprobe, Rhodamine B was added into complex to obtain fluorescent signal changes. Our results demonstrated that the established method could detect E. coli O157:H7 in the range of 101-107 CFU/mL, and the limit of detection (LOD) was 0.35 CFU/mL in TBST buffer (pH = 7.4). In milk simulation samples, the LOD of this method was 1.03 CFU/mL. Our research provides a promising approach on the detection of E. coli O157:H7.

Influence of milk microbiota on Listeria monocytogenes survival during cheese ripening

This study aimed to compare the three strains of Listeria monocytogenes survival in raw milk cheese and pasteurized milk cheese and to suggest the effect of milk microbiota on survival. L. monocytogenes cell counts decreased in all cheese as ripening time increased, and the survival rate was different for the strains of L. monocytogenes. Furthermore, L. monocytogenes survived longer in raw milk cheese than in pasteurized milk cheese. The difference of bacterial survival in each cheese was independent of Aw or the Lactobacillus spp. populations in cheeses; there was no difference in Aw or Lactobacillus spp. populations in all cheeses. The richness of microbiota in raw milk was little higher than in pasteurized milk, and five phyla (Chloroflexi, Cyanobacteria, Deinococcus-Thermus, Lentisphaerae, and Verrucomicrobia) were present only in raw milk. Also, organic acid-producing bacteria were presented more in pasteurized milk compared with raw milk; thus, the growth of L. monocytogenes was slower in pasteurized milk. In conclusion, differences in the microbial community of milk can affect the growth of L. monocytogenes. Making cheese using raw milk is a risk of L. monocytogenes infection; thus, efforts to prevent growth of L. monocytogenes such as the use of appropriate food additives are required.