Print to detect: a rapid and ultrasensitive phage-based dipstick assay for foodborne pathogens

Foodborne pathogens are a burden to the economy and a constant threat to public health. The ability to rapidly detect the presence of foodborne pathogens is a vital component of any strategy towards establishing a safe and secure food supply chain. Bacteriophages (phages) are viruses capable of infecting and replicating within bacteria in a strain-specific manner. The ubiquitous and selective nature of phages makes them ideal for the detection and biocontrol of bacteria. Therefore, the objective of this research was to develop and test a phage-based paper dipstick biosensor for the detection of various foodborne pathogens in food matrices. The first step was to identify the best method for immobilizing phages on paper such that their biological activity (infectivity) was preserved. It was found that piezoelectric inkjet printing resulted in lower loss of phage infectivity when compared with other printing methods (namely gravure and blade coating) and that ColorLok paper was ideally suited to create functional sensors. The phage-based bioactive papers developed with use of piezoelectric inkjet printing actively lysed their target bacteria and retained this antibacterial activity for up to 1 week when stored at room temperature and 80% relative humidity. These bioactive paper strips in combination with quantitative real-time PCR were used for quantitative determination of target bacteria in broth and food matrices. A phage dipstick was used to capture and infect Escherichia coli O157:H7, E. coli O45:H2, and Salmonella Newport in spinach, ground beef and chicken homogenates, respectively, and quantitative real-time PCR was used to detect the progeny phages. A detection limit of 10-50 colony-forming units per millilitre was demonstrated with a total assay time of 8 h, which was the duration of a typical work shift in an industrial setting. This detection method is rapid and cost-effective, and may potentially be applied to a broad range of bacterial foodborne pathogens. Graphical abstract ᅟ.

Bacteriophages: biosensing tools for multi-drug resistant pathogens

Pathogen detection is of utmost importance in many sectors, such as in the food industry, environmental quality control, clinical diagnostics, bio-defence and counter-terrorism. Failure to appropriately, and specifically, detect pathogenic bacteria can lead to serious consequences, and may ultimately be lethal. Public safety, new legislation, recent outbreaks in food contamination, and the ever-increasing prevalence of multidrug-resistant infections have fostered a worldwide research effort targeting novel biosensing strategies. This review concerns phage-based analytical and biosensing methods targeted towards theranostic applications. We discuss and review phage-based assays, notably phage amplification, reporter phage, phage lysis, and bioluminescence assays for the detection of bacterial species, as well as phage-based biosensors, including optical (comprising SPR sensors and fiber optic assays), electrochemical (comprising amperometric, potentiometric, and impedimetric sensors), acoustic wave and magnetoelastic sensors.

Application of bacteriophages for detection of foodborne pathogens

Bacterial contamination of food products presents a challenge for the food industry and poses a high risk for the consumer. Despite increasing awareness and improved hygiene measures, foodborne pathogens remain a threat for public health, and novel methods for detection of these organisms are needed. Bacteriophages represent ideal tools for diagnostic assays because of their high target cell specificity, inherent signal-amplifying properties, easy and inexpensive production, and robustness. Every stage of the phage lytic multiplication cycle, from the initial recognition of the host cell to the final lysis event, may be harnessed in several ways for the purpose of bacterial detection. Besides intact phage particles, phage-derived affinity molecules such as cell wall binding domains and receptor binding proteins can serve for this purpose. This review provides an overview of existing phage-based technologies for detection of foodborne pathogens, and highlights the most recent developments in this field, with particular emphasis on phage-based biosensors.

Bacteriophages for detection and control of bacterial pathogens in food and food-processing environment

This chapter presents recent advances in bacteriophage research and their application in the area of food safety. Section 1 describes general facts on phage biology that are relevant to their application for control and detection of bacterial pathogens in food and environmental samples. Section 2 summarizes the recently acquired data on application of bacteriophages to control growth of bacterial pathogens and spoilage organisms in food and food-processing environment. Section 3 deals with application of bacteriophages for detection and identification of bacterial pathogens. Advantages of bacteriophage-based methods are presented and their shortcomings are discussed. The chapter is intended for food scientist and food product developers, and people in food inspection and health agencies with the ultimate goal to attract their attention to the new developing technology that has a tremendous potential in providing means for producing wholesome and safe food.

Bacteriophage-based biosorbents coupled with bioluminescent ATP assay for rapid concentration and detection of Escherichia coli

Wild type T4 bacteriophage and recombinant T4 bacteriophages displaying biotin binding peptide (BCCP) and cellulose binding module (CBM) on their heads were immobilized on nano-aluminum fiber-based filter (Disruptor), streptavidin magnetic beads and microcrystalline cellulose, respectively. Infectivity of the immobilized phages was investigated by monitoring the phage-mediated growth inhibition of bioluminescent E. coli B and cell lysis using bioluminescent ATP assay. The results showed that phage immobilization resulted in a partial loss of infectivity as compared with the free phage. Nevertheless, the use of a biosorbent based on T4 bacteriophage immobilized on Disruptor filter coupled with a bioluminescent ATP assay allowed simultaneous concentration and detection of as low as 6 x 10(3)cfu/mL of E. coli in the sample within 2h with high accuracy (CV=1-5% in log scale). Excess of interfering microflora at levels 60-fold greater than the target organism did not affect the results when bacteriophage was immobilized on the filter prior to concentration of bacterial cells.

Oriented immobilization of bacteriophages for biosensor applications

A method was developed for oriented immobilization of bacteriophage T4 through introduction of specific binding ligands into the phage head using a phage display technique. Fusion of the biotin carboxyl carrier protein gene (bccp) or the cellulose binding module gene (cbm) with the small outer capsid protein gene (soc) of T4 resulted in expression of the respective ligand on the phage head. Recombinant bacteriophages were characterized in terms of infectivity. It was shown that both recombinant phages retain their lytic activity and host range. However, phage head modification resulted in a decreased burst size and an increased latent period. The efficiency of bacteriophage immobilization with streptavidin-coated magnetic beads and cellulose-based materials was investigated. It was shown that recombinant bacteriophages form specific and strong bonds with their respective solid support and are able to specifically capture and infect the host bacterium. Thus, the use of immobilized BCCP-T4 bacteriophage for an Escherichia coli B assay using a phage multiplication approach and real-time PCR allowed detection of as few as 800 cells within 2 h.

Optimization and validation of a simple method using P22::luxAB bacteriophage for rapid detection of Salmonella enterica serotypes A, B, and D in poultry samples

A simple method was developed for the fast and inexpensive detection of Salmonella Typhimurium using a recombinant P22::luxAB phage. All the steps from phage production to detection were considered. A strain of Salmonella Typhimurium harboring the prophage P22::luxAB was grown in batch culture to produce spontaneously the recombinant bacteriophage. Batch production to stationary phase was better for propagation of the phage and led to a total population of 4.3 x 10(9) (+/-4.3 x 10(9)) PFU/ml of P22, including only 1.4 x 10(6) (+/-1 x 10(6)) PFU/ml harboring the luxAB genes. After preenrichment, a simple four-step bioassay was tested and optimized for several parameters. The detection limit of the luminometer was only 5 x 10(2) (+/-1.75 x 10(2)) CFU Salmonella Typhimurium per ml, but increased to 1.5 x 10(4) (+/-1.17 x 10(4)) CFU Salmonella Typhimurium per ml when the cells were in a complex matrix. The detection limit after the preenrichment was 6.5 x 10(3) (+/-1.5 x 10(3)) CFU Salmonella Typhimurium per ml, but the detection limit after the preenrichment also increased markedly to 1.65 x 10(5) (+/-0.15 x 10(5)) CFU Salmonella Typhimurium per ml when Salmonella Typhimurium was in a complex matrix. Finally, the bioassay was applied to the detection of Salmonella Typhimurium LT2 in 14 different feed and environmental samples (including duck feed, litters, and feces) spiked either before or after the preenrichment process. It was possible to detect Salmonella Typhimurium LT2 in all samples within 16 h.

Evaluation of a rapid microbial detection method via phage lytic amplification assay coupled with Live/Dead fluorochromic stains

AIMS

To develop a method for rapid detection of bacteria via bacteriophage amplification coupled with exogenous fluorochromic stains.

METHODS AND RESULTS

A method for the rapid detection of bacteria was developed which consisted of exposing the sample suspected to contain target cells to host-specific phage. After at least one infection cycle, bacteria known to be infected by the phage (helper cells) were added and the number of nascent phage particles was estimated using the Live/Dead BacLight Bacterial Viability kit. Using Pseudomonas aeruginosa, it was shown that the dead helper cell population following phage infection was proportional to the initial number of target cells present in the original sample. Approximately 1 x 10(1) CFU per ml of P. aeruginosa could be detected within 4 h without the need for enrichment.

CONCLUSIONS

The phage lytic amplification assay coupled with exogenous fluorochromic stains was able to detect approx. 1 x 10(1) CFU per ml of the target bacterium within 4 h.

SIGNIFICANCE AND IMPACT OF THE STUDY

A method to detect low number of bacterial cells in a sample within 4 h without the need for enrichment was developed.

Bacteriophage control of foodborne bacteriat

Bacteriophages are measurable components of the natural microflora in the food production continuum from the farm to the retail outlet. Phages are remarkably stable in these environments and are readily recovered from soil, sewage, water, farm and processing plant effluents, feces, and retail foods. Purified high-titer phage lysates have been used for the species-specific control of bacteria during the pre- and postharvest phases of food production and storage. For example, the inhibition of the phytopathogens Erwinia amylovara and Xanthomonas campestris has reduced the incidence of diseases such as fire blight in apples and bacterial spot of tomato and peaches. Research on preslaughter treatment of food animals has demonstrated phage control of salmonellosis in chickens, enteropathogenic Escherichia coli infections in calves, piglets, and lambs, and E. coli O157:H7 shedding by beef cattle. Phages have also been applied to control the growth of pathogens such as Listeria monocytogenes, Salmonella, and Campylobacter jejuni in a variety of refrigerated foods such as fruit, dairy products, poultry, and red meats. Phage control of spoilage bacteria (e.g., Pseudomonas spp. and Brochothrix thermosphacta) in raw chilled meats can result in a significant extension of storage life. Phage biocontrol strategies for food preservation have the advantages of being self-perpetuating, highly discriminatory, natural, and cost-effective. Some of the drawbacks of biopreservation with phages are a limited host range, the requirement for threshold numbers of the bacterial targets, phage-resistant mutants, and the potential for the transduction of undesirable characteristics from one bacterial strain to another. Most research to date has involved experimentally infected plants and animals or artificially inoculated foods. This technology must be transferred to the field and to commercial environments to assess the possibility of controlling natural contaminants under more realistic production and processing conditions.

Bacteriophages as biocontrol agents in food

Bacteriophages possess attributes that appear to be attractive to those searching for novel ways to control foodborne pathogens and spoilage organisms. These phages have a history of safe use, can be highly host specific, and replicate in the presence of a host. Campylobacter, Salmonella, and Listeria monocytogenes and various spoilage organisms have responded to phage control on some foods. However, the use of phages as biocontrol agents is complicated by factors such as an apparent requirement for a threshold level of host before replication can proceed and by suboptimal performance, at best, at temperatures beneath the optimum for the host. This review is a summary of the information on these issues and includes brief descriptions of alternative phage-based strategies for control of foodborne pathogens.