Depending on where they show up, microorganisms can kill us or create delicacies
Microbes in food make most people think of contamination, and with good reason: the list of dangerous microbes that can turn up in food is long.
Instructor Evelyn Gutierrez and her colleagues at the School of Nutrition and Food Sciences at the Louisiana State University AgCenter (Baton Rouge) recently studied E. coli O157:H7, Hepatitis A, Norovirus, Salmonella, Vibrio vulnificus and microorganisms that cause spoilage in foods. “With new pathogens emerging in foods, probably the main challenge is the development of new technologies to reduce or eliminate pathogens from the food chain,” says Gutierrez. She explains, “We perform analysis to validate the food process, to evaluate if specific procedures are controlling, reducing or eliminating biological hazards.”
The critical need for such testing arises from increasing demand. John Donaghy, corporate food safety microbiologist for Nestlé, headquartered in Vevey, Switzerland, says, “The public health burden of foodborne illness is huge—causing, for example, approximately 48 million cases of illness each year in the United States.” He adds, “In Europe, the story is similar—5400 foodborne outbreaks reported in 2012, resulting in 55,453 human cases, 5118 hospitalizations and 41 deaths.”
Diana Spitznagel, global product manager for biomonitoring systems at Merck Life Science in Eppelheim, Germany, adds, “With the increasing population and food demand, the problem of health issues due to contaminated food will continue to rise, and antimicrobial resistance of pathogens is increasing.” The complexity of the food-illness puzzle also tests scientists. “A major challenge is the linking of illness to a particular pathogen or specific food,” Donaghy says. “This is not always possible; hence many illnesses have an unknown causative agent.”
Microbial contamination can come from many steps during food preparation. Deepa Thakar, national food technical sales manager at EMSL Analytical in Hillside, Ill., says, “Harmful bacteria can enter the production process at various steps, and they are highly adaptable to different environments.”
Not all microbes are hazardous, however. Gutierrez points out that the dangerous microbes make up “a very little proportion of the microorganisms universe.” She adds, “There are a great number of desirable microorganisms, including yeast to produce beer or bread and mold, that give blue cheese its characteristic flavor, aroma and color.” Some condiments—including Louisiana’s famous hot sauces—also rely on microorganisms. “Limited information is available regarding the natural fermentation of the red hot chili pepper mash,” Gutierrez says. “[For] the past few years, I’ve been working on isolating and identifying microorganisms involved in hot-sauce fermentation.” She points out that this research is “still a work in progress, but it has been quite a journey.”
Keeping foods safe from life-threatening microbes requires advanced methods and systems. (Image courtesy of Nestlé.)
Instead of battling microbial contamination in food after the fact, the food industry wants to prevent it. “The focus should not only be on testing but also on prevention of outbreaks,” says Spitznagel. “This requires hygienic conditions for [food] handling staff and [for preparation] areas, as well as putting safety processes into place and keeping high standards.” The intricacy of the industry, however, makes this impossible in many cases.
“Food chains become very complex with increased globalization,” Spitznagel says. “Sometimes it is hard to find the source of contamination.” As greater numbers of food products are made, such as those that are ready to eat, tests must be developed that can detect not only microbes, but various additives and other possible contaminants. “This adds complexity to the testing parameters and methods,” Spitznagel says. “The workflow can be very long, but fast answers are required.” She adds, “Testing should be very fast to be able to recall products which have already gone to the market.”
PCR can be used to develop very specific tests for microbes in foods. (Image courtesy of Bio-Rad.)
For fast testing of complicated samples, experts need a variety of tools. Merck Life Science makes a wide range of culture media, as well as what Spitznagel calls “cheap and simple immunoassays, which require no automation for pathogen detection.” The production of the culture media is ISO (International Organization for Standardization) controlled, she says, which “reduces the customer’s incoming quality control tests.” For the immunoassays, she adds, “No special training is needed, no instrumentation is necessary, and they shorten traditional workflow by one day.”
To keep track of contamination in work areas, Merck Life Science provides a range of air samplers, including a handheld device that counts microbes.
The power of PCR
No matter what experts have tried, food testing remains imperfect. According to Donaghy, “The production of safe food is not guaranteed by testing alone—absence of evidence is not evidence of absence.” Microbial testing has statistical limitations, and when companies test they must use the best tests available. The need for more testing also fuels the need for faster methods. “Many traditional culture methods are slow and labor intense, taking up to five days to confirm a positive finding,” says Donaghy.
Rather than using culture methods, foods can be tested for microbes with the polymerase chain reaction (PCR). “There have been many advances in the area of molecular diagnostics for foodborne pathogens,” Donaghy says. “Reverse transcriptase—RT-PCR—and quantitative—qPCR—are now widely applied for detection of the many bacterial pathogens and are also used to circumvent the issues with nonculturable foodborne viruses.” Scientists develop PCR tests to target specific genes.
Both traditional methods of microbiology and PCR provide high sensitivity, says Jean-François Mouscadet, R&D manager at Bio-Rad’s Food Science Division outside Paris, but “microbiological methods take usually 24 hours more than PCR.”
PCR-based tests also provide high specificity. “These assays can be designed to detect a genus, a species, a serovar or a strain,” says Mouscadet. “The specificity of PCR is unmatched by other methods.” Scientists can also design PCR assays that detect multiple types of bacteria in one test.
The PCR approach comes with some challenges. “The DNA extraction has to be robust to show good efficacy with all kinds of food matrices,” says Mouscadet. “We developed a universal lysis buffer for DNA extraction, but suppliers like us need to remain very reactive to constantly adapt and validate their solutions for unique matrices.”
To expand the use of PCR-based tests in food analysis, the technology needs even easier workflows. Bio-Rad’s real-time PCR-based iQ-Check assays can be automated with the iQ-Check Prep automation platform. “Using this instrument, it is possible to run all food testing assays from Bio-Rad with a true walk-away solution and unmatched throughput,” Mouscadet says.
Stretching the science
Dangerous microbes must be identified and characterized, and instruments must be developed to analyze them more quickly. The analysis process must also adapt to the changing microbes of concern.
Beyond safety, the study of how microbes end up in and impact foods is an important area of science in itself. Gutierrez says, “My favorite part of microbiology is how microorganisms can change the environment they grow in and create something completely different.”
Mike May is a freelance writer and editor living in Ohio. He can be reached at [email protected].