A bacteriophage detection tool for viability assessment of Salmonella cells

Binding activity and specificity of tail fiber protein 35Q for Salmonella pullorum

Salmonella, a prevalent pathogen with significant implications for the poultry industry and food safety, presents a global public health concern. The rise in antibiotic resistance has exacerbated the challenge of prevention. Accurate and sensitive detection methods are essential in combating Salmonella infections. Bacteriophages, viruses capable of targeting and destroying bacteria, leverage their host specificity for accurate microbial detection. Notably, the tail fiber protein of bacteriophages plays a crucial role in recognizing specific hosts, making it a valuable tool for targeted microbial detection. This study focused on the tail fiber protein 35Q of Salmonella pullorum (SP) bacteriophage YSP2, identified through protein sequencing and genome analysis. Bioinformatics analysis revealed similarities between 35Q and other Salmonella bacteriophage tail fiber proteins. The protein was successfully expressed and purified using an Escherichia coli expression system, and its binding activity and specificity were confirmed. ELISA assays and adsorption experiments demonstrated that 35Q interacts with the outer membrane protein (OMP) receptor on bacterial surfaces. This investigation provides valuable insights for targeted Salmonella detection, informs the development of specific therapeutics, and enhances our understanding of the interaction between Salmonella bacteriophages and their hosts.

FTA-LAMP based biosensor for a rapid in-field detection of Globodera pallida-the pale potato cyst nematode

The combination of a sensitive and specific magnetoresistive sensing device with an easy DNA extraction method and a rapid isothermal amplification is presented here targeting the on-site detection of Globodera pallida, a potato endoparasitic nematode. FTA-cards were used for DNA extraction, LAMP was the method developed for DNA amplification and a nanoparticle functionalized magnetic-biosensor was used for the detection. The combinatorial effect of these three emerging technologies has the capacity to detect G. pallida with a detection limit of one juvenile, even when mixed with other related species. This combined system is far more interesting than what a single technology can provide. Magnetic biosensors can be combined with any DNA extraction protocol and LAMP forming a new solution to target G. pallida. The probe designed in this study consistently distinguished G. pallida (∆Vac binding/Vac sensor above 1%) from other cyst nematodes (∆Vac binding/Vac sensor below 1%). It was confirmed that DNA either extracted with FTA-cards or Lab extraction Kit was of enough quantity and quality to detect G. pallida whenever present (alone or in mixed samples), ensuring probe specificity and sensitivity. This work provides insights for a new strategy to construct advanced devices for pathogens in-field diagnostics. LAMP runs separately but can be easily integrated into a single device.

Recent Developments in Lateral Flow Assays for Salmonella Detection in Food Products: A Review

Salmonellosis is a disease transmitted by contaminated food and is one of the leading causes of infections worldwide, making the early detection of Salmonella of crucial importance for public health. However, current detection methods are laborious and time-consuming, thus impacting the entire food supply chain and leading to production losses and economic sanctions. To mitigate these issues, a number of different biosensors have been developed, including lateral flow assays (LFAs), which have emerged as valuable tools in pathogen detection due to their portability, ease of use, time efficiency, and cost effectiveness. The performance of LFAs has been considerably enhanced by the development of new nanomaterials over the years. In this review, we address the principles and formats of the assay and discuss future prospects and challenges with an emphasis on LFAs developed for the detection of different Salmonella serovars in food.

Advances on diagnosis of Helicobacter pylori infections

The association of Helicobacter pylori to several gastric diseases, such as chronic gastritis, peptic ulcer disease, and gastric cancer, and its high prevalence worldwide, raised the necessity to use methods for a proper and fast diagnosis and monitoring the pathogen eradication. Available diagnostic methods can be classified as invasive or non-invasive, and the selection of the best relies on the clinical condition of the patient, as well as on the sensitivity, specificity, and accessibility of the diagnostic test. This review summarises all diagnostic methods currently available, including the invasive methods: endoscopy, histology, culture, and molecular methods, and the rapid urease test (RUT), as well as the non-invasive methods urea breath test (UBT), serological assays, biosensors, and microfluidic devices and the stool antigen test (SAT). Moreover, it lists the diagnostic advantages and limitations, as well as the main advances for each methodology. In the end, research on the development of new diagnostic methods, such as bacteriophage-based H. pylori diagnostic tools, is also discussed.

Development of a Novel Phagomagnetic-Assisted Isothermal DNA Amplification System for Endpoint Electrochemical Detection of Listeria monocytogenes

The hitherto implemented Listeria monocytogenes detection techniques are cumbersome or require expensive non-portable instrumentation, hindering their transposition into on-time surveillance systems. The current work proposes a novel integrated system resorting to loop-mediated isothermal amplification (LAMP), assisted by a bacteriophage P100-magnetic platform, coupled to an endpoint electrochemical technique, towards L. monocytogenes expeditious detection. Molybdophosphate-based optimization of the bacterial phagomagnetic separation protocol allowed the determination of the optimal parameters for its execution (pH 7, 25 °C, 32 µg of magnetic particles; 60.6% of specific capture efficiency). The novel LAMP method targeting prfA was highly specific, accomplishing 100% inclusivity (for 61 L. monocytogenes strains) and 100% exclusivity (towards 42 non-target Gram-positive and Gram-negative bacteria). As a proof-of-concept, the developed scheme was successfully validated in pasteurized milk spiked with L. monocytogenes. The phagomagnetic-based approach succeeded in the selective bacterial capture and ensuing lysis, triggering Listeria DNA leakage, which was efficiently LAMP amplified. Methylene blue-based electrochemical detection of LAMP amplicons was accomplished in 20 min with remarkable analytical sensitivity (1 CFU mL^-1). Hence, the combined system presented an outstanding performance and robustness, providing a 2.5 h-swift, portable, cost-efficient detection scheme for decentralized on-field application.

Development of a phage-based electrochemical biosensor for detection of Escherichia coli O157: H7 GXEC-N07

Escherichia coli (E. coli) O157:H7 is one of the most important foodborne pathogens that causing severe foodborne diseases. With the development of foodborne diseases, there is an urgent need to seek new methods for early detection and monitoring of E. coli O157:H7. In this study, an electrochemical biosensor using phage EP01 as the recognition agent for detection of E. coli O157:H7 GXEC-N07 was established due to the specificity and high efficiency of phage EP01 in recognizing GXEC-N07. The biosensor was developed by depositing phages conjugated carboxyl graphene oxide (CFGO) and conductive carbon black (CB) onto the surface of glass carbon electrodes (GCEs). When detecting GXEC-N07 in the concentration range of 10² ∼ 10⁷ CFU/mL, the biosensor showed good linearity with a low detection limit of 11.8 CFU/mL, and the whole progress was in less than 30 min. The biosensor was successfully applied to the quantitative detection of GXEC-N07 in fresh milk and raw pork. The recovery values ranged from 60.8 % to 114.2 %. The biosensor provides a rapid, specific, low cost, and label free tool for E. coli O157:H7 GXEC-N07 detection. It is expected to become a powerful method for the detection of bacteria that threatening food safety and public health security.

Induction of Viable but Non-Culturable State in Clinically Relevant Staphylococci and Their Detection with Bacteriophage K

Prosthetic joint infections are frequently associated with biofilm formation and the presence of viable but non-culturable (VBNC) bacteria. Conventional sample culturing remains the gold standard for microbiological diagnosis. However, VBNC bacteria lack the ability to grow on routine culture medium, leading to culture-negative results. Bacteriophages are viruses that specifically recognize and infect bacteria. In this study, we wanted to determine if bacteriophages could be used to detect VBNC bacteria. Four staphylococcal strains were cultured for biofilm formation and transferred to low-nutrient media with different gentamycin concentrations for VBNC state induction. VBNC bacteria were confirmed with the BacLight^TM viability kit staining. Suspensions of live, dead, and VBNC bacteria were incubated with bacteriophage K and assessed in a qPCR for their detection. The VBNC state was successfully induced 8 to 19 days after incubation under stressful conditions. In total, 6.1 to 23.9% of bacteria were confirmed alive while not growing on conventional culturing media. During the qPCR assay, live bacterial suspensions showed a substantial increase in phage DNA. No detection was observed in dead bacteria or phage non-susceptible E. coli suspensions. However, a reduction in phage DNA in VBNC bacterial suspensions was observed, which confirmed the detection was successful based on the adsorption of phages.

Magnetic microbead enzyme-linked immunoassay based on phage encoded protein RBP 41-mediated for rapid and sensitive detection of Salmonella in food matrices

Rapid and sensitive quantitative detection methods are required to monitor and detect Salmonella throughout the food supply chain and early prevention of foodborne disease outbreaks. In this study, a magnetic microbead enzyme-linked immunoassay (MELISA) based on phage receptor binding protein was developed for rapid enrichment and detection of Salmonella in complex food matrices. RBP 41 from phage T102 acted as a species-specific recognition element for Salmonella by exploiting its strong binding capacity to Salmonella surface receptors. RBP 41-MBs were prepared by coupling recombinant RBP 41 with MBs and used to separate and enrich Salmonella cells from spiked food samples. The captured complexes were further integrated with ELISA procedures by HRP-labeled anti-Salmonella antibody for rapid and accurate detection of Salmonella. The whole method took <1.5 h and the detection limit was 10 CFU/mL. Therefore, MELISA was successfully developed for the detection of Salmonella in various spiked food samples (skim milk, lettuce, and chicken breast). The ELISA reaction process of this method was carried out on magnetic beads. It simplified the process of the traditional ELISA method and reduces the reaction time. This study expanded the use of phage-associated proteins and demonstrated the promising prospects for practical applications in the detection of foodborne pathogens.

Overview of VBNC, a survival strategy for microorganisms

Microorganisms are exposed to a wide variety of stress factors in their natural environments. Under that stressful conditions, they move into a viable but nonculturable (VBNC) state to survive and maintain the vitality. At VBNC state, microorganisms cannot be detected by traditional laboratory methods, but they can be revived under appropriate conditions. Therefore, VBNC organisms cause serious food safety and public health problems. To date, it has been determined that more than 100 microorganism species have entered the VBNC state through many chemical and physical factors. During the last four decades, dating from the initial detection of the VBNC condition, new approaches have been developed for the induction, detection, molecular mechanisms, and resuscitation of VBNC cells. This review evaluates the current data of recent years on the inducing conditions and detection methods of the VBNC state, including with microorganisms on the VBNC state, their virulence, pathogenicity, and molecular mechanisms.

Properties of a Novel Salmonella Phage L66 and Its Application Based on Electrochemical Sensor-Combined AuNPs to Detect Salmonella

Salmonella is widespread in nature and poses a significant threat to human health and safety. Phage is considered as a new tool for the control of food-borne pathogens. In this study, Salmonella phage L66 (phage L66) was isolated from sewage by using Salmonella Typhimurium ATCC 14028 as the host bacterium, and its basic properties were obtained by biological and bioinformatics analysis. Phage L66 had a broad host spectrum, with an optimal infection complex of 0.1 and an optimal adsorption rate of 90.06%. It also exhibited thermal stability between 30 °C~60 °C and pH stability pH from 3 to 12, and the average lysis amount was 46 PFU/cell. The genome sequence analysis showed that the genome length of phage L66 was 157,675 bp and the average GC content was 46.13%. It was predicted to contain 209 genes, 97 of which were annotated with known functions based on the evolutionary analysis, and phage L66 was attributed to the Kuttervirus genus. Subsequently, an electrochemical sensor using phage L66 as a recognition factor was developed and the working electrode GDE-AuNPs-MPA-Phage L66 was prepared by layer-by-layer assembly for the detection of Salmonella. The slope of the impedance was 0.9985 within the scope from 20 to 2 × 10⁷ CFU/mL of bacterial concentration. The minimum detection limit of the method was 13 CFU/mL, and the average spiked recovery rate was 102.3% with a relative standard deviation of 5.16%. The specificity and stability of this sensor were excellent, and it can be applied for the rapid detection of Salmonella in various foods. It provides a phage-based electrochemical biosensor for the detection of pathogenic bacteria.

Potential of bacteriophage proteins as recognition molecules for pathogen detection

Bacterial pathogens are leading causes of infections with high mortality worldwide having a great impact on healthcare systems and the food industry. Gold standard methods for bacterial detection mainly rely on culture-based technologies and biochemical tests which are laborious and time-consuming. Regardless of several developments in existing methods, the goal of achieving high sensitivity and specificity, as well as a low detection limit, remains unaccomplished. In past years, various biorecognition elements, such as antibodies, enzymes, aptamers, or nucleic acids, have been widely used, being crucial for the pathogens detection in different complex matrices. However, these molecules are usually associated with high detection limits, demand laborious and costly production, and usually present cross-reactivity. (Bacterio)phage-encoded proteins, especially the receptor binding proteins (RBPs) and cell-wall binding domains (CBDs) of endolysins, are responsible for the phage binding to the bacterial surface receptors in different stages of the phage lytic cycle. Due to their remarkable properties, such as high specificity, sensitivity, stability, and ability to be easily engineered, they are appointed as excellent candidates to replace conventional recognition molecules, thereby contributing to the improvement of the detection methods. Moreover, they offer several possibilities of application in a variety of detection systems, such as magnetic, optical, and electrochemical. Herein we provide a review of phage-derived bacterial binding proteins, namely the RBPs and CBDs, with the prospect to be employed as recognition elements for bacteria. Moreover, we summarize and discuss the various existing methods based on these proteins for the detection of nosocomial and foodborne pathogens.

A Phage Receptor-Binding Protein as a Promising Tool for the Detection of Escherichia coli in Human Specimens

Escherichia coli is a problematic pathogen that causes life-threatening diseases, being a frequent causative agent of several nosocomial infections such as urinary tract and bloodstream infections. Proper and rapid bacterial identification is critical for allowing prompt and targeted antimicrobial therapy. (Bacterio)phage receptor-binding proteins (RBPs) display high specificity for bacterial surface epitopes and, therefore, are particularly attractive as biorecognition elements, potentially conferring high sensitivity and specificity in bacterial detection. In this study, we elucidated, for the first time, the potential of a recombinant RBP (Gp17) to recognize E. coli at different viability states, such as viable but not culturable cells, which are not detected by conventional techniques. Moreover, by using a diagnostic method in which we combined magnetic and spectrofluorimetric approaches, we demonstrated the ability of Gp17 to specifically detect E. coli in various human specimens (e.g., whole blood, feces, urine, and saliva) in about 1.5 h, without requiring complex sample processing.

Suggestion for a new bacteriophage genus for the Klebsiella pneumoniae phage vB_KpnS-Carvaje

This work describes the newly isolated Klebsiella pneumoniae phage vB_KpnS-Carvaje that presents unique features in relation to other phages reported to date. These findings provide new insights into the diversity and evolutionary pathways of Klebsiella phages. The genome characterization of the Carvaje phage revealed that its genome length is approximately 57 kb with 99 open reading frames (ORFs), 33 of which have assigned functions while 66 are unknown. This phage differs from other sequenced Klebsiella phages, showing the closest resemblance (up to 65.32%) with Salmonella phages belonging to the Nonanavirus and Sashavirus genera. Comparisons at the amino acid level and phylogeny analysis among homologous genomes indicate that the Klebsiella Carvaje phage forms a novel sister taxon within the node of the Nonanaviruses and Sashaviruses cluster. Due to the unique features of the Carvaje phage, we propose the constitution of a new genus within the Caudoviricetes class. Further studies include the exploitation of this phage and its identified proteins for the control of Klebsiella infections and as recognition molecules in diagnostic methods.

Recent Advances in Electrochemical Biosensors for the Detection of Salmonellosis: Current Prospective and Challenges

Salmonellosis is a major cause of foodborne infections, caused by Salmonella, posing a major health risk. It possesses the ability to infiltrate the food supply chain at any point throughout the manufacturing, distribution, processing or quality control process. Salmonella infection has increased severely and requires effective and efficient methods for early monitoring and detection. Traditional methods, such as real-time polymerase chain reaction and culture plate, consume a lot of time and are labor-intensive. Therefore, new quick detection methods for on-field applications are urgently needed. Biosensors provide consumer-friendly approaches for quick on-field diagnoses. In the last few years, there has been a surge in research into the creation of reliable and advanced electrochemical sensors for the detection of Salmonella strains in food samples. Electrochemical sensors provide extensive accuracy and reproducible results. Herein, we present a comprehensive overview of electrochemical sensors for the detection of Salmonella by focusing on various mechanisms of electrochemical transducer. Further, we explain new-generation biosensors (microfluidics, CRISPR- and IOT-based) for point-of care applications. This review also highlights the limitations of developing biosensors in Salmonella detection and future possibilities.

Combined detection of molecular and serological signatures of viral infections: The dual assay concept

The recent worldwide spread of viral infections has highlighted the need for accurate, fast, and inexpensive disease diagnosis and monitorization methods. Current diagnostics tend to focus either on molecular or serological testing. In this work we propose a dual detection assay approach for viral diseases, where both serological and molecular assays are combined in a single analysis performed on a magnetoresistive system. This type of assay guarantees an accurate assessment of the infection phase, saving time and costs associated with multiple independent tests. Zika and dengue viruses were used as model diseases for the validation of the system. Human IgG anti-zika and anti-dengue antibodies were successfully detected in infected patients' serum, using a novel approach combining competitive and sandwich strategies in a magnetoresistive portable platform. Specificity and sensitivity values of 100% were obtained. Calibration curves with dynamic ranges between 10 ng/mL and 1 μg/mL were established achieving LODs of 1.26 and 1.38 nM for IgG anti-ZIKV and anti-DENV antibodies, respectively. Viral RNA detection down to a few hundreds of pM was also successfully carried out after the design of specific oligo probes and primers for RT-PCR amplification. Dual assays were performed for both viruses, where viral RNA and anti-virus antibodies in serum samples were simultaneously detected. The results obtained for the detection of the molecular and serological targets in the dual assay format show no significant difference between the ones obtained individually, proving the feasibility and accuracy of the dual detection assay. This assay format represents a new paradigm in viral infections diagnostics.

The application and research progress of bacteriophages in food safety

The abuse of antibiotics and the emergence of drug-resistant bacteria aggravate the problem of food safety. Finding a safe and efficient antibiotic substitute is an inevitable demand for ensuring the safety of animal-derived food. Bacteriophages are a kind of virus that can infect bacteria, fungi or actinomycetes. They have the advantages of simple structure, strong specificity and non-toxic side effects to human body. Bacteriophages can not only differentiate live cells from dead ones, but also detect bacteria in a viable but nonculturable state. These characteristics make bacteriophages more and more widely used in food industry. This paper describes the concept and characteristics of bacteriophages, introduces the application of bacteriophages in pre-harvest production, food processing, storage and sales. Several methods of bacteriophage detection of foodborne pathogens are listed. Finally, the advantages and limitations of bacteriophages in food industry are summarized, and the application prospect of bacteriophages in food industry are prospected.

New analytical methods using carbon-based nanomaterials for detection of Salmonella species as a major food poisoning organism in water and soil resources

Salmonella is one of the most prevalent causing agents of food- and water-borne illnesses, posing an ongoing public health threat. These food-poisoning bacteria contaminate the resources at different stages such as production, aggregation, processing, distribution, as well as marketing. According to the high incidence of salmonellosis, effective strategies for early-stage detection are required at the highest priority. Since traditional culture-dependent methods and polymerase chain reaction are labor-intensive and time-taking, identification of early and accurate detection of Salmonella in food and water samples can prevent significant health economic burden and lessen the costs. The immense potentiality of biosensors in diagnosis, such as simplicity in operation, the ability of multiplex analysis, high sensitivity, and specificity, have driven research in the evolution of nanotechnology, innovating newer biosensors. Carbon nanomaterials enhance the detection sensitivity of biosensors while obtaining low levels of detection limits due to their possibility to immobilize huge amounts of bioreceptor units at insignificant volume. Moreover, conjugation and functionalization of carbon nanomaterials with metallic nanoparticles or organic molecules enables surface functional groups. According to these remarkable properties, carbon nanomaterials are widely exploited in the development of novel biosensors. To be specific, carbon nanomaterials such as carbon nanotubes, graphene and fullerenes function as transducers in the analyte recognition process or surface immobilizers for biomolecules. Herein the potential application of carbon nanomaterials in the development of novel Salmonella biosensors platforms is reviewed comprehensively. In addition, the current problems and critical analyses of the future perspectives of Salmonella biosensors are discussed.

Overview of Rapid Detection Methods for Salmonella in Foods: Progress and Challenges

Salmonella contamination in food production and processing is a serious threat to consumer health. More and more rapid detection methods have been proposed to compensate for the inefficiency of traditional bacterial cultures to suppress the high prevalence of Salmonella more efficiently. The contamination of Salmonella in foods can be identified by recognition elements and screened using rapid detection methods with different measurable signals (optical, electrical, etc.). Therefore, the different signal transduction mechanisms and Salmonella recognition elements are the key of the sensitivity, accuracy and specificity for the rapid detection methods. In this review, the bioreceptors for Salmonella were firstly summarized and described, then the current promising Salmonella rapid detection methods in foodstuffs with different signal transduction were objectively summarized and evaluated. Moreover, the challenges faced by these methods in practical monitoring and the development prospect were also emphasized to shed light on a new perspective for the Salmonella rapid detection methods applications.

An Alternative to Antibiotics: Selected Methods to Combat Zoonotic Foodborne Bacterial Infections

Pathogenic bacteria contaminating food or animal feed cause serious economic losses in the health sector as well as is in the agriculture and food industry. The development of bacterial resistance due to the misuse of antibiotics and chemicals, especially in the farm industry, can bring dangerous effects for the global population therefore new safe biological antimicrobial solutions are urgently needed. In this paper, we investigate biological alternatives to antibiotics against foodborne pathogens. The most promising alternatives include antimicrobial proteins, bacteriophages, probiotics, and plant-based substances. Each described group of substances is efficient against specific foodborne bacteria and has a preferred use in an explicit application. The advantages and drawbacks of each method are outlined in the final section. Biological antibacterial solutions are usually easily degradable. In contrast to antibiotics or chemical/physical methods, they are also far more specific. When introducing new antibacterial methods it is crucial to check their safety and ability to induce resistance mechanisms. Moreover, it is important to assess its activity to inhibit or kill in viable but nonculturable cells (VBNC) state and biofilm forms. VBNC bacteria are considered a threat to public health and food safety due to their possibility of remaining viable and virulent. Biological alternatives to antibiotics complete the majority of the advantages needed for a safe and efficient antimicrobial product. However, further research is necessary to fully implement those solutions to the market.

A systematic review from basics to omics on bacteriophage applications in poultry production and processing

The growing human population is currently facing an unprecedented challenge on global food production and sustainability. Despite recognizing poultry as one of the most successful and rapidly growing food industries to address this challenge; poultry health and safety remain major issues that entail immediate attention. Bacterial diseases including colibacillosis, salmonellosis, and necrotic enteritis have become increasingly prevalent during poultry production. Likewise, outbreaks caused by consumption of undercooked poultry products contaminated with zoonotic bacterial pathogens such as Salmonella, Campylobacter and Listeria, are a serious public health concern. With antimicrobial resistance problem and restricted use of antibiotics in food producing animals, bacteriophages are increasingly recognized as an attractive natural antibacterial alternative. Bacteriophages have recently shown promising results to treat diseases in poultry, reduce contamination of carcasses, and enhance the safety of poultry products. Omics technologies have been successfully employed to accurately characterize bacteriophages and their genes/proteins important for interaction with bacterial hosts. In this review, the potential of using lytic bacteriophages to mitigate the risk of major poultry-associated bacterial pathogens are explored. This study also explores challenges associated with the adoption of this technology by industries. Furthermore, the impact of omics approaches on studying bacteriophages, their host interaction and applications is discussed.

Rapid determination of viable but non-culturable Campylobacter jejuni in food products by loop-mediated isothermal amplification coupling propidium monoazide treatment

Campylobacter is the leading cause of foodborne human diarrhea worldwide. This microbe in the viable but non-culturable (VBNC) state can evade detection by routinely used culture-based methods and remain viable for extended periods of time. Bacteria in this dormancy state can resume their metabolic activity and virulence by resuscitation under favorable conditions, and subsequently cause infections. In this study, an assay combining loop-mediated isothermal amplification (LAMP) and propidium monoazide (PMA) treatment was developed for the detection and quantification of VBNC C. jejuni in agri-foods. PMA-qLAMP targeting the hipO gene demonstrated 100% high specificity to C. jejuni. A linear detection of C. jejuni was achieved between 8.77 × 102 and 8.77 × 07 CFU/mL with a coefficient of determination (R2) of 0.9956, indicating a good quantitative capacity. C. jejuni was effectively induced into the VBNC state by osmotic stress (i.e., 7% NaCl, w/v) over 48 h. VBNC C. jejuni cells were spiked into three representative food products and determined by PMA-qLAMP coupled with plating assay. The detection limits of PMA-qLAMP were 1.58 × 102 CFU/mL in milk, 3.78 × 102 CFU/g in chicken breast meat, and 4.33 × 102 CFU/g in romaine lettuce. PMA-qLAMP demonstrated rapid (25-40 min), specific (100% inclusivity and 100% exclusivity) and sensitive (~102 CFU/mL) determination of VBNC C. jejuni. This method can be applied in the agri-food industry to decrease the risks related to the consumption of contaminated agri-foods with pathogenic bacteria in the VBNC state and reduce the burden of C. jejuni infections to public health.

Biosensors for European Zoonotic Agents: A Current Portuguese Perspective

Emerging and recurrent outbreaks caused by zoonotic agents pose a public health risk. They result in morbidity and mortality in humans and significant losses in the livestock and food industries. This highlights the need for rapid surveillance methods. Despite the high reliability of conventional pathogen detection methods, they have high detection limits and are time-consuming and not suitable for on-site analysis. Furthermore, the unpredictable spread of zoonotic infections due to a complex combination of risk factors urges the development of innovative technologies to overcome current limitations in early warning and detection. Biosensing, in particular, is highlighted here, as it offers rapid and cost-effective devices for use at the site of infection while increasing the sensitivity of detection. Portuguese research in biosensors for zoonotic pathogens is the focus of this review. This branch of research produces exciting and innovative devices for the study of the most widespread pathogenic bacteria. The studies presented here relate to the different classes of pathogens whose characteristics and routes of infection are also described. Many advances have been made in recent years, and Portuguese research teams have increased publications in this field. However, biosensing still needs to be extended to other pathogens, including potentially pandemic viruses. In addition, the use of biosensors as part of routine diagnostics in hospitals for humans, in animal infections for veterinary medicine, and food control has not yet been achieved. Therefore, a convergence of Portuguese efforts with global studies on biosensors to control emerging zoonotic diseases is foreseen for the future.

Strategies for Surface Immobilization of Whole Bacteriophages: A Review

Bacteriophage immobilization is a key unit operation in emerging biotechnologies, enabling new possibilities for biodetection of pathogenic microbes at low concentration, production of materials with novel antimicrobial properties, and fundamental research on bacteriophages themselves. Wild type bacteriophages exhibit extreme binding specificity for a single species, and often for a particular subspecies, of bacteria. Since their specificity originates in epitope recognition by capsid proteins, which can be altered by chemical or genetic modification, their binding specificity may also be redirected toward arbitrary substrates and/or a variety of analytes in addition to bacteria. The immobilization of bacteriophages on planar and particulate substrates is thus an area of active and increasing scientific interest. This review assembles the knowledge gained so far in the immobilization of whole phage particles, summarizing the main chemistries, and presenting the current state-of-the-art both for an audience well-versed in bioconjugation methods as well as for those who are new to the field.

Recent Innovations in Bacterial Infection Detection and Treatment

Bacterial infections are a major threat to human health, exacerbated by increasing antibiotic resistance. These infections can result in tremendous morbidity and mortality, emphasizing the need to identify and treat pathogenic bacteria quickly and effectively. Recent developments in detection methods have focused on electrochemical, optical, and mass-based biosensors. Advances in these systems include implementing multifunctional materials, microfluidic sampling, and portable data-processing to improve sensitivity, specificity, and ease of operation. Concurrently, advances in antibacterial treatment have largely focused on targeted and responsive delivery for both antibiotics and antibiotic alternatives. Antibiotic alternatives described here include repurposed drugs, antimicrobial peptides and polymers, nucleic acids, small molecules, living systems, and bacteriophages. Finally, closed-loop therapies are combining advances in the fields of both detection and treatment. This review provides a comprehensive summary of the current trends in detection and treatment systems for bacterial infections.

Biosensors for rapid detection of Salmonella in food: A review

Salmonella is one of the main causes of foodborne infectious diseases, posing a serious threat to public health. It can enter the food supply chain at various stages of production, processing, distribution, and marketing. High prevalence of Salmonella necessitates efficient and effective approaches for its identification, detection, and monitoring at an early stage. Because conventional methods based on plate counting and real-time polymerase chain reaction are time-consuming and laborious, novel rapid detection methods are urgently needed for in-field and on-line applications. Biosensors provide many advantages over conventional laboratory assays in terms of sensitivity, specificity, and accuracy, and show superiority in rapid response and potential portability. They are now recognized as promising alternative tools and one of the most on-site applicable and end user-accessible methods for rapid detection. In recent years, we have witnessed a flourishing of studies in the development of robust and elaborate biosensors for detection of Salmonella in food. This review aims to provide a comprehensive overview on Salmonella biosensors by highlighting different signal-transducing mechanisms (optical, electrochemical, piezoelectric, etc.) and critically analyzing its recent trends, particularly in combination with nanomaterials, microfluidics, portable instruments, and smartphones. Furthermore, current challenges are emphasized and future perspectives are discussed.

Optimization of T4 phage engineering via CRISPR/Cas9

A major limitation hindering the widespread use of synthetic phages in medical and industrial settings is the lack of an efficient phage-engineering platform. Classical T4 phage engineering and several newly proposed methods are often inefficient and time consuming and consequently, only able to produce an inconsistent range of genomic editing rates between 0.03-3%. Here, we review and present new understandings of the CRISPR/Cas9 assisted genome engineering technique that significantly improves the genomic editing rate of T4 phages. Our results indicate that crRNAs selection is a major rate limiting factor in T4 phage engineering via CRISPR/Cas9. We were able to achieve an editing rate of > 99% for multiple genes that functionalizes the phages for further applications. We envision that this improved phage-engineering platform will accelerate the fields of individualized phage therapy, biocontrol, and rapid diagnostics.

A sandwich-type bacteriophage-based amperometric biosensor for the detection of Shiga toxin-producing Escherichia coli serogroups in complex matrices

Immuno-based biosensors are a popular tool designed for pathogen screening and detection. The current antibody-based biosensors employ direct, indirect, or sandwich detection approaches; however, instability, cross-reactivity, and high-cost render them unreliable and impractical. To circumvent these drawbacks, here we report a portable sandwich-type bacteriophage-based amperometric biosensor, which is highly-specific to various Shiga toxin-producing Escherichia coli (STEC) serogroups. Environmentally isolated and biotinylated bacteriophages were directly immobilized onto a streptavidin-coated screen-printed carbon electrode (SPCE), which recognized and captured viable target cells. Samples (50 μL) were transferred to these bacteriophage-functionalized SPCEs (12 min, room temp) before sequentially adding a bacteriophage-gold nanoparticle solution (20 μL), H2O2 (40 mM), and 1,1'-ferrocenedicarboxylic acid for amperometric tests (100 mV s-1) and analysis (ANOVA and LSD, P < 0.05). The optimum biotin concentration (10 mM) retained 94.47% bacteriophage viability. Non-target bacteria (Listeria monocytogenes and Salmonella Typhimurium) had delta currents below the threshold of a positive detection. With less than 1 h turn-around time, the amperometric biosensor had a detection limit of 10-102 CFU mL-1 for STEC O157, O26, and O179 strains and R 2 values of 0.97, 0.99, and 0.87, respectively, and a similar detection limit was observed in complex matrices, 10-102 CFU g-1 or mL-1 with R 2 values of 0.98, 0.95, and 0.76, respectively. The newly developed portable amperometric biosensor was able to rapidly detect viable target cells at low inoculum levels, thus providing an inexpensive and improved alternative to the current immuno- and laboratory-based STEC screening methods.

Multiple Bacteria Identification in the Point-of-Care: an Old Method Serving a New Approach

The accurate diagnosis of bacterial infections is of critical importance for effective treatment decisions. Due to the multietiologic nature of most infectious diseases, multiplex assays are essential for diagnostics. However, multiplexability in nucleic acid amplification-based methods commonly resorts to multiple primers and/or multiple reaction chambers, which increases analysis cost and complexity. Herein, a polymerase chain reaction (PCR) offer method based on a universal pair of primers and an array of specific oligonucleotide probes was developed through the analysis of the bacterial 16S ribosomal RNA gene. The detection system consisted of DNA hybridization over an array of magnetoresistive sensors in a microfabricated biochip coupled to an electronic reader. Immobilized probes interrogated single-stranded biotinylated amplicons and were obtained using asymmetric PCR. Moreover, they were magnetically labelled with streptavidin-coated superparamagnetic nanoparticles. The benchmarking of the system was demonstrated to detect five major bovine mastitis-causing pathogens: Escherichia coli, Klebsiella sp., Staphylococcus aureus, Streptococcus uberis, and Streptococcus agalactiae. All selected probes proved to specifically detect their respective amplicon without significant cross reactivity. A calibration curve was performed for S. agalactiae, which demonstrates demonstrating a limit of detection below 30 fg/µL. Thus, a sensitive and specific multiplex detection assay was established, demonstrating its potential as a bioanalytical device for point-of-care applications.

An aptamer-based magnetic flow cytometer using matched filtering

Facing unprecedented population-ageing, the management of noncommunicable diseases (NCDs) urgently needs a point-of-care (PoC) testing infrastructure. Magnetic flow cytometers are one such solution for rapid cancer cellular detection in a PoC setting. In this work, we report a giant magnetoresistive spin-valve (GMR SV) biosensor array with a multi-stripe sensor geometry and matched filtering to improve detection accuracy without compromising throughput. The carefully designed sensor geometry generates a characteristic signature when cells labeled with magnetic nanoparticles (MNPs) pass by thus enabling multi-parametric measurement like optical flow cytometers (FCMs). Enumeration and multi-parametric information were successfully measured across two decades of throughput (37 - 2730 cells/min). 10-μm polymer microspheres were used as a biomimetic model where MNPs and MNP-decorated polymer conjugates were flown over the GMR SV sensor array and detected with a signal-to-noise ratio (SNR) as low as 2.5 dB due to the processing gain afforded by the matched filtering. The performance was compared against optical observation, exhibiting a 92% detection efficiency. The system achieved a 95% counting accuracy for biomimetic models and 98% for aptamer-based pancreatic cancer cell detection. This system demonstrates the ability to perform reliable flow cytometry toward PoC diagnostics to benefit NCD control plans.

Comparison of stress conditions to induce viable but non-cultivable state in Salmonella

Salmonella can enter on the viable but non-culturable state (VBNC), characterized by the loss of ability to grow in routine culture media hindering detection by conventional methods and underestimation of the pathogen. Despite advances in research done so far, studies comparing conditions that lead Salmonella into the VBNC state are scarce. The main objective of this study was to evaluate different stresses to induce Salmonella to the VNBC state. Osmotic (1.2 M NaCl), acid (peracetic acid, 5.66 mg/mL) and oxidative (hydrogen peroxide, 1.20 mg/mL) stress were used at 4 °C to induce Salmonella enterica serovars Enteritidis and Typhimurium to the VBNC state. The culturability loss was monitored in the brain heart infusion (BHI) broth and agar, and the viability was determined by fluorescence microscopy, using the Live/Dead® kit, and by flow cytometry. Besides, the morphological characterization by atomic force microscopy (AFM) was performed. Storage in 1.2 M NaCl at 4 °C induced the VBNC state in Salmonella cells for periods longer than 121 days, and the percentage of viable cells has reached above 80.9%. More aggressive stress conditions promoted by peracetic acid and hydrogen peroxide induced the VBNC state in periods of, at most 0.14 day, and resulted in percentages of 8.5% to 45.5% viable cells, respectively. The counts of viable cells in the flow cytometer corroborate the results obtained by microscopic counts. The VBNC cells obtained in 1.2 M NaCl at 4 °C showed morphological changes, reducing the size and changing the morphology from bacillary to coccoid. No morphological change was observed on the cells stressed by acid or oxidant compounds.

Real-time detection of foodborne bacterial viability using a colorimetric bienzyme system in food and drinking water

Foodborne bacterial infection poses a serious threat to human health. As most diseases are caused by living bacteria, real-time assessment of bacterial viability is vitally important to the public health sector. Herein, we developed a simple and novel colorimetric assay based on the Glucose oxidase (GOD)/Horseradish peroxidase (HRP) bienzyme system for real-time monitoring of bacterial viability in food and drinking water. This bienzyme system is free of any chemical synthesis and only requires 3 sample handling steps. The color response is easily observable with the naked eye or recordable with a smartphone for precise determination of bacterial viability. The proposed strategy was validated with various bacteria both Gram-positive and Gram-negative, indicating its capability for broad-spectrum bacteria viability detection. Therefore, the proposed strategy shows promise for rapid and reliable quality control in food and drinking water.

Phage based electrochemical detection of Escherichia coli in drinking water using affinity reporter probes

The monitoring of drinking water for indicators of fecal contamination is crucial for ensuring a safe supply. In this study, a novel electrochemical method was developed for the rapid and sensitive detection of Escherichia coli (E. coli) in drinking water. This strategy is based on the use of engineered bacteriophages (phages) to separate and concentrate target E. coli when conjugated with magnetic beads, and to facilitate the detection by expressing gold binding peptides fused alkaline phosphatase (GBPs-ALP). The fusion protein GBPs-ALP has both the enzymatic activity and the ability to directly bind onto a gold surface. This binding-peptide mediated immobilization method provided a novel and simple approach to immobilize proteins on a solid surface, requiring no post-translational modifications. The concentration of E. coli was determined by measuring the activity of the ALP on gold electrodes electrochemically using linear sweep voltammetry (LSV). This approach was successfully applied in the detection of E. coli in drinking water. We were able to detect 105 CFU mL-1 of E. coli within 4 hours. After 9 hours of preincubation, 1 CFU of E. coli in 100 mL of drinking water was detected with a total assay time of 12 hours. This approach compares favorably to the current EPA method and has the potential to be applied to detect different bacteria in other food matrices.

Induction and Resuscitation of the Viable but Non-culturable (VBNC) State in Acidovorax citrulli, the Causal Agent of Bacterial Fruit Blotch of Cucurbitaceous Crops

Acidovorax citrulli is a gram-negative bacterium that infects a wide range of cucurbits causing bacterial fruit blotch (BFB) disease. Copper-based compounds are the most widely-used chemicals for managing BFB and other bacterial diseases in the field. Many bacteria can enter a viable but non-culturable (VBNC) state in response to stress, including exposure to copper, and recover the culturability when favorable conditions return. The present study demonstrates that A. citrulli strain AAC00-1 is able to enter into the VBNC state by treatment with different concentrations of copper sulfate. It took 3 h, 5 and 15 days for all viable cells to lose culturability upon exposure to copper sulfate concentrations of 50, 10, and 5 μM, respectively. The VBNC A. citrulli cells regained culturability when the Cu2+ ions were removed by chelation with EDTA or by transfer of cells to LB broth, a cell-free supernatant from a suspension of AAC00-1, oligotrophic media amended with casein hydrolysate or watermelon seedling juice. We also found that the VBNC cells induced by Cu2+ were unable to colonize or infect watermelon seedlings directly, but the resuscitated cells recovered full virulence equivalent to untreated bacterial cells in the log phase. To the best of our knowledge, this is the first report on the VBNC state in A. citrulli and the factors that facilitate resuscitation and restoration of pathogenicity.

Going Viral: Emerging Opportunities for Phage-Based Bacterial Control in Water Treatment and Reuse

Water security to protect human lives and support sustainable development is one of the greatest global challenges of this century. While a myriad of water pollutants can impact public health, the greatest threat arises from pathogenic bacteria that can be harbored in different components of water treatment, distribution, and reuse systems. Bacterial biofilms can also promote water infrastructure corrosion and biofouling, which substantially increase the cost and complexity of many critical operations. Conventional disinfection and microbial control approaches are often insufficient to keep up with the increasing complexity and renewed relevance of this pressing challenge. For example, common disinfectants cannot easily penetrate and eradicate biofilms, and are also relatively ineffective against resistant microorganisms. The use of chemical disinfectants is also curtailed by regulations aimed at minimizing the formation of harmful disinfection byproducts. Furthermore, disinfectants cannot be used to kill problematic bacteria in biological treatment processes without upsetting system performance. This underscores the need for novel, more precise, and more sustainable microbial control technologies. Bacteriophages (phages), which are viruses that exclusively infect bacteria, are the most abundant (and perhaps the most underutilized) biological resource on Earth, and hold great promise for targeting problematic bacteria. Although phages should not replace broad-spectrum disinfectants in drinking water treatment, they offer great potential for applications where selective targeting of problematic bacteria is warranted and antimicrobial chemicals are either relatively ineffective or their use would result in unintended detrimental consequences. Promising applications for phage-based biocontrol include selectively suppressing bulking and foaming bacteria that hinder activated sludge clarification, mitigating proliferation of antibiotic resistant strains in biological wastewater treatment systems where broad-spectrum antimicrobials would impair pollutant biodegradation, and complementing biofilm eradication efforts to delay corrosion and biofouling. Phages could also mitigate harmful cyanobacteria blooms that produce toxins in source waters, and could also serve as substitutes for the prophylactic use of antibiotics and biocides in animal agriculture to reduce their discharge to source waters and the associated selective pressure for resistant bacteria. Here, we consider the phage life cycle and its implications for bacterial control, and elaborate on the biochemical basis of such potential application niches in the water supply and reuse cycle. We also discuss potential technological barriers for phage-based bacterial control and suggest strategies and research needs to overcome them.

Flow cytometry applications in water treatment, distribution, and reuse: A review

Ensuring safe and effective water treatment, distribution, and reuse requires robust methods for characterizing and monitoring waterborne microbes. Methods widely used today can be limited by low sensitivity, high labor and time requirements, susceptibility to interference from inhibitory compounds, and difficulties in distinguishing between viable and non-viable cells. Flow cytometry (FCM) has recently gained attention as an alternative approach that can overcome many of these challenges. This article critically and systematically reviews for the first time recent literature on applications of FCM in water treatment, distribution, and reuse. In the review, we identify and examine nearly 300 studies published from 2000 to 2018 that illustrate the benefits and challenges of using FCM for assessing source-water quality and impacts of treatment-plant discharge on receiving waters, wastewater treatment, drinking water treatment, and drinking water distribution. We then discuss options for combining FCM with other indicators of water quality and address several topics that cut across nearly all applications reviewed. Finally, we identify priority areas in which more work is needed to realize the full potential of this approach. These include optimizing protocols for FCM-based analysis of waterborne viruses, optimizing protocols for specifically detecting target pathogens, automating sample handling and preparation to enable real-time FCM, developing computational tools to assist data analysis, and improving standards for instrumentation, methods, and reporting requirements. We conclude that while more work is needed to realize the full potential of FCM in water treatment, distribution, and reuse, substantial progress has been made over the past two decades. There is now a sufficiently large body of research documenting successful applications of FCM that the approach could reasonably and realistically see widespread adoption as a routine method for water quality assessment.

Bacterial biosensing: Recent advances in phage-based bioassays and biosensors

In nature, different types of bacteria including pathogenic and beneficial ones exist in different habitats including environment, plants, animals, and humans. Among these, the pathogenic bacteria should be detected at earlier stages of infection; however, the conventional bacterial detection procedures are complex and time-consuming. In contrast, the advanced molecular approaches such as polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA) have significantly reduced the detection time; nevertheless, such approaches are not acceptable to a large extent and are mostly laborious and expensive. Therefore, the development of fast, inexpensive, sensitive, and specific approaches for pathogen detection is essential for different applications in food industry, clinical diagnosis, biological defense and counter-terrorism. To this end, the novel sensing approaches involving bacteriophages as recognition elements are receiving immense consideration owing to their high degree of specificity, accuracy, and reduced assay times. Besides, the phages are easily produced and are tolerant to extreme pH, temperature, and organic solvents as compared to antibodies. To date, several phage-based assays and sensors have been developed involving different systems such as quartz crystal microbalance, magnetoelastic platform, surface plasmon resonance, and electrochemical methods. This review highlights different taxonomic species and genera of phages infecting eight common disease-causing bacterial genera. It further overviews the most recent advancements in phage-based sensing assays and sensors. Likewise, it elaborates various whole-phage and phage components-based assays. Overall, this review emphasizes the importance of electrochemical biosensors as simple, reliable, cost-effective, and accurate tools for bacterial detection.

The absence or presence of a lytic coliphage affects the response of Escherichia coli to heat, chlorine, or UV exposure

Disinfection aims at maximal inactivation of target organisms and the sustainable suppression of their regrowth. Whereas many disinfection efforts achieve efficient inactivation when the effect is measured directly after treatment, there are questions about the sustainability of this effect. One aspect is that the treated bacteria might recover and regain the ability to grow. In an environmental context, another question is how amenable surviving bacteria are to predation by omnipresent bacteriophages. Provisional data suggested that bacteria when subjected to sublethal heat stress might develop a phage-resistant phenotype. The result made us wonder about the susceptibility to phage-mediated lysis for bacteria exposed to a gradient of chlorine and UV-LED disinfection strengths. Whereas bacteria exposed to low sublethal chlorine doses still underwent phage-mediated lysis, the critical chlorine Ct of 0.5 mg min/L eliminated this susceptibility and induced phage resistance in the cells that survived treatment. In the case of UV, even the smallest tested dose of 2.8 mJ/cm² abolished phage lysis leading to direct regrowth. Results suggest that bacteria surviving disinfection might have higher environmental survival chances directly after treatment compared to non-treated cells. A reason could possibly lie in their compromised metabolism that is essential for phage replication.

Lab-on-Chip Devices: Gaining Ground Losing Size

Portable analytical devices are notably gaining relevance in the panorama of urgent testing. Such devices have the potential to play an important role as easy-to-handle tools in critical situations. Epidemic infectious disease agents (e.g., Ebola virus, Coronavirus, Zika virus) could be controlled more easily by testing travelers on-site at the country borders to prevent outbreaks from spreading. The increasing incidence of hospital-acquired infections caused by antibiotic resistant pathogens could be minimized by point-of-care microbial analysis as well as rapid screening tests of bacteria resistance. The threat of bioterrorism using novel unknown bioweapons has never been so high, thus, in-the-field early identification of the biological agent is crucial for triggering a coordinated response. Food allergies are a growing public health concern-allergic reactions can result in anaphylactic shock, which can prove fatal in minutes-thus, the ability to test foods for common allergens, rapidly and locally, before ingestion, would improve food safety for those with allergies. Lab-on-chip devices are becoming widely available for diverse applications and are becoming increasingly affordable. However, to shrink in price and size simultaneously, some trade-offs must be made. In this Perspective, we present considerations about product specifications, design concepts, and application scenarios.

A CMOS Front-End With Integrated Magnetoresistive Sensors for Biomolecular Recognition Detection Applications

The development of giant magnetoresistive (GMR) sensors has demonstrated significant advantages in nanomedicine, particularly for ultrasensitive point-of-care diagnostics. To this end, the detection system is required to be compact, portable, and low power consuming at the same time that a maximum signal to noise ratio is maintained. This paper reports a CMOS front-end with integrated magnetoresistive sensors for biomolecular recognition detection applications. Based on the characterization of the GMR sensor's signal and noise, CMOS building blocks (i.e., current source, multiplexers, and preamplifier) were designed targeting a negligible noise when compared with the GMR sensor's noise and a low power consumption. The CMOS front-end was fabricated using AMS [Formula: see text] technology and the magnetoresistive sensors were post-fabricated on top of the CMOS chip with high yield ( [Formula: see text]). Due to its low circuit noise (16 [Formula: see text]) and overall equivalent magnetic noise ([Formula: see text]), the full system was able to detect 250 nm magnetic nanoparticles with a circuit imposed signal-to-noise ratio degradation of only -1.4 dB. Furthermore, the low power consumption (6.5 mW) and small dimensions ([Formula: see text] ) of the presented solution guarantees the portability of the detection system allowing its usage at the point-of-care.

Detection of BCG bacteria using a magnetoresistive biosensor: A step towards a fully electronic platform for tuberculosis point-of-care detection

Tuberculosis is one of the major public health concerns. This highly contagious disease affects more than 10.4 million people, being a leading cause of morbidity by infection. Tuberculosis is diagnosed at the point-of-care by the Ziehl-Neelsen sputum smear microscopy test. Ziehl-Neelsen is laborious, prone to human error and infection risk, with a limit of detection of 10⁴ cells/mL. In resource-poor nations, a more practical test, with lower detection limit, is paramount. This work uses a magnetoresistive biosensor to detect BCG bacteria for tuberculosis diagnosis. Herein we report: i) nanoparticle assembly method and specificity for tuberculosis detection; ii) demonstration of proportionality between BCG cell concentration and magnetoresistive voltage signal; iii) application of multiplicative signal correction for systematic effects removal; iv) investigation of calibration effectiveness using chemometrics methods; and v) comparison with state-of-the-art point-of-care tuberculosis biosensors. Results present a clear correspondence between voltage signal and cell concentration. Multiplicative signal correction removes baseline shifts within and between biochip sensors, allowing accurate and precise voltage signal between different biochips. The corrected signal was used for multivariate regression models, which significantly decreased the calibration standard error from 0.50 to 0.03log₁₀ (cells/mL). Results show that Ziehl-Neelsen detection limits and below are achievable with the magnetoresistive biochip, when pre-processing and chemometrics are used.

Differential enumeration of subpopulations in concentrated frozen and lyophilized cultures of Lactobacillus delbrueckii ssp. bulgaricus

Differential enumeration of subpopulations in concentrated frozen and lyophilized cultures of Lactobacillus delbrueckii ssp. bulgaricus ND02 derived from 2 propagation procedures was determined. The subpopulations consisted of 3 categories (physiological states): viable cells capable of forming colonies on agar plates (VC+), viable cells incapable of forming colonies on agar plates (VC-), widely referred to as viable but nonculturable (VBNC) cells, and nonviable or dead cells (NVC). Counts of VC+ were recorded using a conventional plate count procedure. A fluorescent vital staining procedure that discriminates between viable (VC+ and VC-) and NVC cells was used to determine the number of viable and nonviable cells. Both propagation procedures had 2 variables: in procedure (P)1, the propagation medium was rich in yeast extract (4.0%) and the pH was maintained at 5.7; in P2, the medium was devoid of yeast extract and the pH was maintained at 5.1. The results showed that post-propagation operations-concentration of cells by centrifugation and subsequent freezing or lyophilization of cell concentrate-induced different degrees of transience from VC+ to VC- states in cells derived from P1 and P2. Compared with cells derived from P2, cells from P1 were more labile to stress associated with centrifugation, freezing, and lyophilization, as revealed by differential counting.

Bacteriophages: the possible solution to treat infections caused by pathogenic bacteria

Since their discovery in 1915, bacteriophages have been used to treat bacterial infections in animals and humans because of their unique ability to infect their specific bacterial hosts without affecting other bacterial populations. The research carried out in this field throughout the 20th century, largely in Georgia, part of USSR and Poland, led to the establishment of phage therapy protocols. However, the discovery of penicillin and sulfonamide antibiotics in the Western World during the 1930s was a setback in the advancement of phage therapy. The misuse of antibiotics has reduced their efficacy in controlling pathogens and has led to an increase in the number of antibiotic-resistant bacteria. As an alternative to antibiotics, bacteriophages have become a topic of interest with the emergence of multidrug-resistant bacteria, which are a threat to public health. Recent studies have indicated that bacteriophages can be used indirectly to detect pathogenic bacteria or directly as biocontrol agents. Moreover, they can be used to develop new molecules for clinical applications, vaccine production, drug design, and in the nanomedicine field via phage display.

Giant Magnetoresistive Biosensors for Time-Domain Magnetorelaxometry: A Theoretical Investigation and Progress Toward an Immunoassay

Magnetorelaxometry (MRX) is a promising new biosensing technique for point-of-care diagnostics. Historically, magnetic sensors have been primarily used to monitor the stray field of magnetic nanoparticles bound to analytes of interest for immunoassays and flow cytometers. In MRX, the magnetic nanoparticles (MNPs) are first magnetized and then the temporal response is monitored after removing the magnetic field. This new sensing modality is insensitive to the magnetic field homogeneity making it more amenable to low-power portable applications. In this work, we systematically investigated time-domain MRX by measuring the signal dependence on the applied field, magnetization time, and magnetic core size. The extracted characteristic times varied for different magnetic MNPs, exhibiting unique magnetic signatures. We also measured the signal contribution based on the MNP location and correlated the coverage with measured signal amplitude. Lastly, we demonstrated, for the first time, a GMR-based time-domain MRX bioassay. This approach validates the feasibility of immunoassays using GMR-based MRX and provides an alternative platform for point-of-care diagnostics.

Combining phagomagnetic separation with immunoassay for specific, fast and sensitive detection of Staphylococcus aureus

A Staphylococcus aureus (S. aureus)-specific lytic bacteriophage P-S. aureus-9, isolated from an environmental water sample, was assembled on magnetic beads for capturing S. aureus from samples through magnetic separation. Horseradish Peroxidase (HRP) labeled immunoglobulin (IgG) antibodies were used to detect the captured S. aureus by reacting with protein A on S. aureus followed by colorimetric signals, which were generated from the catalytic reaction between HRP and the substrate 3,3',5,5'-Tetramethylbenzidine (TMB). Under optimal conditions, the calibration curve was linear from 1.0×10⁴ to 1.0×10⁶CFUmL^-1. The limit of detection (LOD) for the assay was 2.47×10³CFUmL^-1 and 8.86×10³CFUmL^-1 of S. aureus in PBS and apple juice, respectively. Moreover, the whole assay revealed outstanding specificity towards S. aureus, without any interference of common pathogenic bacteria, and can be completed within 90min without any pre-enrichment. As far as known, it was the first time to detect S. aureus based on the double site recognition of bacteriophage and mammal IgG. The novel approach has shown good potentials for a rapid, specific, cheap and simple detection of S. aureus in food samples.