Extended Enrichment Procedures Can Be Used To Define False-Negative Probabilities for Cultural Gold Standard Methods for Salmonella Detection, Facilitating Comparisons between Gold Standard and Alternative Methods

Microfluidics for detection of food pathogens: recent trends and opportunities

Safe and healthy food is the fundamental right of every citizen. Problems caused by foodborne pathogens have always raised a threat to food safety and human health. Centers for Disease Control and Prevention (CDC) estimates that around 48 million people are affected by food intoxication, and 3000 people succumb to death. Hence, it is inevitable that an approach that is efficient, reliable, sensitive, and rapid approach that can replace the conventional analytical methods such as microbiological and biochemical methods, high throughput next-generation sequence (NGS), polymerase chain reaction (PCR), and enzyme-linked immunosorbent assay (ELISA), etc. Even though the accuracy of conventional methods is high, it is tedious; increased consumption of reagents/samples, false positives, and complex operations are the drawbacks of these methods. Microfluidic devices have shown remarkable advances in all branches of science. They serve as an alternative to conventional ways to overcome the abovementioned drawbacks. Furthermore, coupling microfluidics can improve the efficiency and accuracy of conventional methods such as surface plasma resonance, loop-mediated isothermal amplification, ELISA, and PCR. This article reviewed the progress of microfluidic devices in the last ten years in detecting foodborne pathogens. Microfluidic technology has opened the research gateway for developing low-cost, on-site, portable, and rapid assay devices. The article includes the application of microfluidic-based devices to identify critical food pathogens and briefly discusses the necessary research in this area.

A Salmonella Microfluidic Chip Combining Non-Contact Eddy Heater and 3D Fan-Shaped Mixer with Recombinase Aided Amplification

Foodborne pathogenic bacteria have become a worldwide threat to human health, and rapid and sensitive bacterial detection methods are urgently needed. In this study, a facile microfluidic chip was developed and combined with recombinase-aided amplification (RAA) for rapid and sensitive detection of Salmonella typhimurium using a non-contact eddy heater for dynamic lysis of bacterial cells and a 3D-printed fan-shaped active mixer for continuous-flow mixing. First, the bacterial sample was injected into the chip to flow through the spiral channel coiling around an iron rod under an alternating electromagnetic field, resulting in the dynamic lysis of bacterial cells by this non-contact eddy heater to release their nucleic acids. After cooling to ~75 °C, these nucleic acids were continuous-flow mixed with magnetic silica beads using the fan-shaped mixer and captured in the separation chamber using a magnet. Finally, the captured nucleic acids were eluted by the eluent from the beads to flow into the detection chamber, followed by RAA detection of nucleic acids to determine the bacterial amount. Under the optimal conditions, this microfluidic chip was able to quantitatively detect Salmonella typhimurium from 1.1 × 10² to 1.1 × 10⁵ CFU/mL in 40 min with a detection limit of 89 CFU/mL and might be prospective to offer a simple, low-cost, fast and specific bacterial detection technique for ensuring food safety.

Rapid Screening for Salmonella in Raw Pet Food by Loop-Mediated Isothermal Amplification

ABSTRACT

Raw pet food, composed of raw meat and vegetables, has increased in popularity in recent years. Multiple surveys and frequent recalls indicate that this commodity has a high risk of contamination with Salmonella and other foodborne pathogens. Improved screening methods are needed to meet the growing demand for testing. This matrix verification study aimed to apply a Salmonella loop-mediated isothermal amplification (LAMP) method, recently completed multilaboratory validation in dry dog food, in several raw pet food matrices, following the U.S. Food and Drug Administration (FDA)'s method validation guidelines. Five types of raw pet food, consisting of freeze-dried beef and chicken treats and frozen beef, pork, and turkey complete foods, were evaluated. For each matrix, two sets of ten 25-g test portions (seven inoculated with ≤30 cells of Salmonella Typhimurium and three uninoculated controls) were examined. One set was preenriched in buffered peptone water and the other one was preenriched in lactose broth, which was followed by LAMP screening using two isothermal master mixes (ISO-001 and ISO-004). All results were confirmed by culture as specified in the FDA Bacteriological Analytical Manual (BAM). The LAMP method accurately detected Salmonella in all inoculated test portions of the five raw pet food samples, regardless of the preenrichment broth used. Positive results could be obtained within 4 min of the LAMP run using the ISO-004 master mix. All uninoculated controls tested negative using LAMP or BAM. In addition, one turkey-based complete pet food sample was found to be already contaminated with three Salmonella serovars harboring multiple antimicrobial resistance genes. The Salmonella LAMP method offers a rapid, reliable, and robust tool for routine screening of Salmonella in raw pet food, which will help better ensure product safety and protect public health.

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