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From: Food Quality & Safety magazine, June/July 2011

The Power of Phages

Bacteriophage technology is critical in diagnostic testing for food safety

by J. Stan Bailey, PhD

Image of a recombinant phage protein
Image of a recombinant phage protein

The nature of food and foodborne illness has changed dramatically in the United States over the past century. While various technological advances such as pasteurization and proper canning have all but eliminated some diseases, new causes of foodborne illness are continually being identified.

The Centers for Disease Control and Prevention (CDC) estimates that roughly one out of six Americans, or 48 million people, are sickened by foodborne illness each year. Another 128,000 are hospitalized, and approximately 3,000 die of foodborne diseases every year.

Further, it is estimated that reducing foodborne illness by just 10% would keep about 5 million Americans from getting sick each year, while preventing even a single fatal case of E. coli O157 infection could result in significant cost savings.

As known pathogens continue to build resistance to available therapeutics and new pathogens emerge around the globe, ongoing changes in demographics, globalization, food production and processing, and food consumption patterns require a comprehensive, science-based approach to food safety assurance and testing. Diagnostic labs need approaches that will quickly and reliably detect pathogens with minimal risk for error. Because of this need, there is growing interest in the application of bacteriophage technology in diagnostic testing for food safety.

Identifying Common Pathogens

Outbreaks of disease caused by foodborne pathogens such as Salmonella, E. coli, Listeria, and others clearly have an enormous impact on public health. Unfortunately, effectively eliminating these ever-evolving bacteria from food processing plants can be difficult and costly. Despite rigorous controls put in place by experts at the U.S. Department of Agriculture and the U.S. Food and Drug Administration, we continue to see growth in the number of cases of food-related disease in the United States and around the world. Consider the following:

  • Salmonella, a bacterium that causes one of the most common intestinal infections in the United States (salmonellosis) is implicated in more than one million cases of foodborne disease annually in the United States, according to a 2011 report. Of these cases, approximately 20,000 result in hospitalization and 378 result in death.
  • Once regarded as a rare serotype, Escherichia coli O157:H7 (E. coli O157:H7) today is one of the major contributors to foodborne disease in industrial countries. It has been estimated that each year E. coli O157:H7 causes approximately 62,000 cases of foodborne disease and approximately 1,800 foodborne illness-related hospitalizations in the United States.
  • Disease caused by Listeria monocytogenes (listeriosis) primarily affects pregnant women, newborns, and adults with weakened immune systems and has one of the highest fatality rates among all foodborne bacterial diseases.

Many available approaches for identifying foodborne pathogens are sufficient and accurate when used correctly. However, associated time lags and/or potential for human error when facilitating the tests can compromise the test results, as can a company’s ability to respond in a manner expedient enough to avoid outbreaks. For instance, results obtained from traditional microbiological culture techniques can only be obtained within three to five days. Additionally, test performance and accuracy can be negatively affected by the number of lab technicians and other specialists physically handling the samples.

Other technologies, including DNA-based polymerase chain reaction assay, immuno-assay, and immuno-latex agglutination, have been developed to address some of these issues and, in most cases, can obtain results within 48 hours. Faster detection, however, is necessary to better manage and prevent outbreaks by stopping the distribution and consumption of infected food more quickly.

Phages are highly specific viruses that use their host bacterial cells as factories for their own replication and have the ability to display peptides or proteins on their surfaces—a technology known as phage display.

Bacteriophage Technology

Detection methods utilizing bacteriophages (phages) can allow food producers to rapidly detect any bacterial pathogens present in their products. These methods also provide an effective means to significantly reduce or prevent contamination of foods with specific pathogenic bacteria, thereby eliminating the risk, or significantly reducing the magnitude and severity, of foodborne illness caused by the consumption of foods contaminated with those bacteria.

Phages are highly specific viruses that use their host bacterial cells as factories for their own replication and have the ability to display peptides or proteins on their surfaces—a technology known as phage display. Phage display can be used as a powerful tool to screen for affinity reagents for all kinds of targets, ranging from small molecules to proteins and even cells. Because phages are host-specific, able only to infect specific species or even strains, phage typing is useful in differentiating bacterial isolates and may be used to identify and characterize outbreak-associated strains. Individual phages may recognize a multitude of different surface-associated molecules.

In a traditional antibody detection approach, for instance, antigens or certain proteins are used to elicit a specific humoral immune response that produces antibodies to the bacterium. These proteins represent one out of several mechanisms that are involved in any given immune response.

By contrast, the recognition elements utilized by phage for identification of their host represent the only possibility to propagate. The proper function of these proteins thereby underlies the highest selective pressure; they are indispensible to phage survival. Their function as “sensing” receptors offers advantages over methods that are based on antibodies: their efficient immobilization, the possibility of using different detection methods due to easy labeling, and the easy regeneration of their functionality after immobilization.

Additionally, the phage proteins can be modified, thus enhancing their stability, affinity, and specificity and facilitating the functionalization of nanoparticles and surfaces. These advantages enable phage recombinant proteins to meet the requirements of sensitivity and stability that are necessary for the detection of bacterial pathogens and food contaminants in their natural matrices.

Replacing antibodies with phage proteins in commercially available diagnostic tests allows for the development of assays capable of detecting even low levels of contamination by dangerous bacteria.

Replacing antibodies with phage proteins in commercially available diagnostic tests allows for the development of assays that can detect even low levels of contamination by dangerous bacteria.

Innovative Screening

While many food testing assays efficiently detect common foodborne pathogens, considerations such as performance, ease of use, speed (time to results), potential for error, degree of automation, and cost are also critical factors that must be taken into account by any food company choosing its technology for pathogen detection.

Phage technology has been available for more than 40 years. However, its effective use in bacterial pathogen detection is relatively recent due to advances in the development of biochemically re-engineered phage proteins, as well as highly specific assays by innovative companies in the space. Thanks to the efforts of expert microbiologists and food safety researchers, phage recombinant proteins can offer unrivaled specificity and sensitivity for the targeted capture and detection of bacteria from a given food sample.

Replacing traditional antibodies with bacteriophage proteins improves the sensitivity and specificity of methods and allows for more rapid detection of bacterial pathogens from a variety of food and environmental samples. This shorter time to detection helps to lower the incidence of foodborne illness outbreaks.

Additionally, recent data show that phage technology is as sensitive as molecular technology in identifying foodborne pathogens. Assays such as the VIDAS UP technology, developed to identify the presence of specific bacterial pathogens using phage proteins, have been incorporated into one simple test, comprising only one broth and one strip. This test can deliver results in as little as eight hours, whereas traditional methods can take up to two days. This approach also has the flexibility of analyzing a broader range of sample sizes, allowing for greater productivity in the lab and more effective management of quality control processes and risk management for the food industry overall.n

Dr. Bailey has written or cowritten more than 500 scientific publications in the area of food microbiology, concentrating on the control of Salmonella in poultry production and processing, Salmonella and Listeria testing methodologies, and rapid methods to detect and identify bacteria in foods. He is director of scientific affairs for bioMérieux Industry. Prior to joining bioMérieux in 2008, he worked as a research scientist for the USDA, Agricultural Research Service, from 1973-2007.

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