Trends in microbiological testing technologies

The poultry industry is shifting towards rapid tests for faster, better, affordable pathogen detection.

BAX System, an automated DNA-based detection system, uses real-time PCR to detect bacteria.
BAX System, an automated DNA-based detection system, uses real-time PCR to detect bacteria.

Increasing regulatory pressure on poultry processors to reduce the incidence of salmonella and campylobacter on carcasses as well as the zero tolerance standard for listeria on ready-to-eat products have made microbial testing an everyday occurrence at poultry plants. Testing technologies are under pressure to be accurate, fast, easy and affordable. In a perfect world, a single test would identify all pathogens from one sample with immediate results. While this "perfect" test has yet to be created, pathogen testing technologies are receiving attention and getting better.

Establishing Safety

Moving from the days of inspecting by sight, smell and touch, the USDA Food Safety and Inspection Service (FSIS) implemented the Hazard Analysis and Critical Control Point (HACCP) inspection system in the 1990s as a scientific approach to counter food borne illnesses caused by unseen bacteria. The FSIS's testing technique, utilizing culture plating, sets the standard of comparison for today's alternative technologies. Still effectively used by many processors, this method can require a significant amount of hands-on work by a microbiological technician and take five or more days to present results.

Plating techniques are more labor intensive than the newer rapid tests, but the costs of materials are typically less. Jim Farr, global pathogen market manager for 3M Microbiology, estimates, "On a global basis, about 50 percent of pathogen testing is done this way. In the U.S., however, that number is much smaller because people have adapted for the benefits that rapid test technologies provide."

Melissa Herbert, poultry market manager, Neogen Corporation, agrees that most integrators, at least domestically, are utilizing rapid testing methods throughout the process to insure that their controls are effective.

Rapid Technologies

Several companies offer a variety of rapid test kits that satisfy some combination of the lofty goals of accuracy, speed, ease and affordability. Dr. Shelly McKee, Auburn University of poultry science, explains that there are two basic types of rapid tests. "You have your gene-based system, like a BAX (a Polymerase Chain Reaction based product from DuPont) and you have the ELISA-based (Enzyme-Linked ImmunoSorbent Assay). With a gene-based system you get everything that is there even if some of the organisms are injured. The more genes present in the sample, then the higher the amplitude, so, that is partially quantitative."

The BAX system from DuPont Qualicon is a DNA-based system that uses Polymerase Chain Reaction (PCR) testing to detect salmonella, campylobacter and other bacteria.

With a PCR system, explains Dr. Scott Russell, poultry processing and products microbiology, University of Georgia, "If you have salmonella in a sample in low numbers, you take the genes and split the bacteria open. If salmonella genes are present you replicate those genes. You don't replicate the organisms because they are dead, but you replicate the genes the DNA until your get a million copies and you can do this in a few hours. Then you can detect if the salmonella DNA is present." PCR provides specific tests that can be done quickly as compared to traditional methodology.

Dr. Amy Smith, technical and registry specialist, DuPont Qualicon, says, "Some of the more progressive poultry companies have moved to using PCR testing for salmonella and listeria because it provides a more reliable result than does a serological assay and is valuable for correctly identifying the presence of Listeria spp. This way, time is not wasted on false results and a sanitization process can be implemented to correct the problem if necessary."

ELISA is a biochemical technique used to detect the presence of an antibody or antigen in a sample. Performing an ELISA involves at least one antibody with specificity for a particular antigen. Following a series of procedures, a substance is added in the final step forcing the enzyme to convert to a detectable signal. In the case of fluorescence ELISA, when a light is shone on the sample, antigen/antibody complexes will fluoresce so the amount of antigen in the sample can be measured.

Dr. Russell explains an antigen test for salmonella, "The ELFA (Enzyme Linked Florescent Assay) procedure combines rinseate from the chicken with a medium and grows the bacteria to a high population. A selective media kills off bacteria other than salmonella and the resulting broth is put into a machine. This is a detection test where an antibody is used to capture the organism. Following a series of rinse steps, the equipment can detect whether or not the bacteria has combined with the antibody exposing its presence."

Another system described by Dr. Russell is the Pathatrix system where metal beads coated with salmonella antibodies are mixed with the test solution. The solution is pumped around the metal beads and the salmonella, if present, actually sticks to them.

Reducing Human Error

A focus on cost-effectiveness can lead plants to evaluate and in some cases reduce staffing. This trend, particularly in smaller facilities, can result in line employees becoming more involved in monitoring for food safety. And that, in turn, contributes to the push for developing easier, less complicated testing systems that can benefit testing procedures in plants of all sizes.

"We are seeing increased concern at the plant level with insuring that not only the product, but the overall processing environment is as free as possible from salmonella and other pathogens," says Herbert. "Neogen is preparing to release a quick test for the detection of salmonella, specifically in bird rinse, that is both easy to use and accurate in this difficult matrix."

Some DNA and RNA rapid tests require highly trained personnel and in some cases very specific laboratory environments, but the trend is to simplify and standardize procedures. Simplification for the reduction of steps required to shorten the time frame, and automation to reduce the levels of technician training necessary and the possibility of human error.

Kevin Habas, global marketing operations manager, 3M Microbiology, says, "The key to some of the rapid technologies is taking the technician variability out of the tests so the manipulations are more automated. The move to be more automated is to eliminate some of the technician variability of sample handling, sample collection and some of the transfer steps to standardize into some kind of module or automation."

International Company Concerns

Standardization goes beyond making testing procedures easier in a single plant. Global safety standards and testing standardization within companies with facilities in multiple countries are becoming issues. For example, Habas points out, a company in Europe doesn't want to have to conduct multiple types of tests within their facilities, "They want to standardize on a couple of testing technologies where they know and trust the results and understand how the product performs on the array of products that they manufacture globally. "It's a global world and there are lots of testing options. But for a big food company, it is a risk assessment and risk management thing where companies like to clear approved alternatives to standard methods that are on the marketplace. It's brand protection for them."

Costs, Trade-Offs, Advantages

Some of the rapid testing methods are coming down in price, but food plants are pragmatic and practical about how they spend their money as far as overall pathogen tests and protocols. A company will use what makes sense within its budget and consider the level of technician training required.

"Expense is all relative," says Habas. "Some of the newer technologies are more expensive typically versus technologies of 20 or 30 years ago but there are trade-offs. It may be simpler or easier to train for the newer technologies, so what some customers will do is use multiple systems in their plant. If they do identify pathogens they may use multiple methods a very affordable system on a day-to-day basis and maybe they have a rapid method to do a confirmation or some quick retesting."

Dr. McKee, agreeing with Habas to a point, adds, "Everybody is after a rapid test; it saves you hours but you have to balance that with the expense, the number of tests you are running and whether you risk a false positive because, for example, with listeria, a false positive will cause you to have a recall that you can't afford."

Shibu Abraham, senior microbiologist, at FMC, talked about customer support offered by suppliers to the poultry industry, "We have a microbiology lab and research and development lab in New Jersey, capable of doing all the testing. We have a BAX system in the lab and can run all the USDA methodologies during installation and trials to verify and validate our system as it is installed in the plant."

As testing technologies progress, Abraham affirms, "Everything is going to get better, faster, smaller, less expensive and when it does, the consumer in the end will benefit. So will the poultry industry with the ability to do get accurate results more efficiently. And better testing will lead to better profit control."

Herbert says, "From ATP testing for sanitation verification to rapid pathogen and general microbial tests, each product that is supplied to the poultry industry must be accurate, easy to use, and cost effective to be a useful part of an organization's pathogen control efforts."

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