FAQ: Microbial Ecology and Foodborne Disease

How do pathogens get into our food?

Pathogenic microorganisms can be introduced at any point in the food chain. Some pathogen contamination is the result of production agriculture conditions, because the farm environment has so many opportunities for contamination that complete control is impossible. Other times, contamination occurs from environmental sources during processing. Some pathogens are introduced during handling and food preparation, either through inadequate human sanitation or through cross-contamination by contact with other foods.

Although the processing methods that foods undergo may inactivate many pathogens, proper food handling after processing remains an important part of microbial control. Some pathogens are common in the production and processing environments, and continuous efforts are needed to design, implement, and verify the effectiveness of control programs.

Why don’t food companies eliminate these pathogens from our food?

For many foods, it is currently impossible to produce a product that is free of pathogens and also in the form desired by consumers. For example, the heat processing necessary to produce shelf-stable canned foods makes these foods very safe, but it also has substantial effects on the food’s sensory characteristics and sometimes its nutritional profile. Some foods cannot withstand rigorous processing for safety and retain acceptable sensory characteristics. Therefore, not all foods are made available in a commercially sterile condition.

In a desire to offer a wide variety of safe, nutritious, and enjoyable foods, food manufacturers continue to study ways to reduce the risk of foodborne pathogens while maintaining a desirable food product. Consumer demand for foods that seem “fresher” has prompted development of a number of alternative processing technologies that use mechanisms other than heat to control pathogens. Although some of these technologies have tremendous potential, it is unlikely that any single technology can be expected to control all pathogens on all foods. Furthermore, even foods that are free of pathogens when they leave the food processing facility may become contaminated during distribution, storage, or preparation.

How does processing control pathogens?

Pathogen control can be divided into three goals: prevent pathogen contamination, inactivate pathogens present in the food, and prevent or limit pathogen growth. Often, food safety management strategies employ a combination of methods to enhance the safety of a particular food.

Companies take numerous steps to prevent or minimize contamination of raw ingredients and unfinished product. These good manufacturing practices (GMPs) include equipment design and cleaning, facility sanitation, worker sanitation, and pest control. Good agricultural practices and appropriate practices during harvest also reduce pathogen contamination of raw materials.

The processing technologies used to inactivate pathogens vary by food product. Foods may be washed or rinsed with organic acids, sanitizers, or other antimicrobial agents. Thermal processing heats a particular food to a specific temperature and holds it at this point for a specified time. Examples of thermal processing include cooking and pasteurization. Nonthermal processing technologies use other means to inactivate pathogens, such as pulsed electric fields, high pressure, or ultraviolet radiation. Other processing methods may change the characteristics of the food in a way to control pathogens. For example, fermentation, drying, and salting all change parameters of the food in a controlled manner to inhibit the pathogen growth.

Food safety management does not end once a food is processed. GMPs are designed to prevent the food from recontamination while it remains at the processing facility. For some foods, certain types of packaging not only protect product quality and facilitate distribution but also prevent contamination and minimize pathogen growth. Storage conditions, such as limited humidity and refrigeration temperatures, are key methods used to prevent or minimize pathogen growth for many foods.

Will new processing technologies eliminate foodborne illness?

No. Even a food free of pathogens when it leaves the processing facility can become contaminated by the time it is consumed. New processing technologies will continue to enhance food safety and quality, but appropriate food handling and preparation practices will always be an essential component of food safety management.

How are the so-called alternative processing technologies different from traditional processing technologies?Do these alternative technologies work?

Traditional food processing has relied primarily on thermal treatments to kill/inactivate microbial contaminants in food. Chemical preservatives and naturally occurring antimicrobial compounds also have been widely used. Unfortunately, these methods result in physical and chemical changes in the food that are not always desirable. Consumer demand for “fresh” products have fueled efforts to develop processing technologies that minimize these sensory and nutritional changes in food.

Like any technology, alternative processing methods have their limitations. Some methods work extremely well for some foods, and not so well for others, depending on the characteristics of the food. Similarly, the mechanism used to inactivate pathogens will be more effective for some pathogens than others. Learning about these limitations is an important part of the research to develop and validate new technologies. Some of these limitations can be overcome with additional research, others cannot. Selecting the proper processing technology for a particular food requires knowledge of the food’s characteristics and the pathogens of concern for that food product.

Does refrigeration prevent pathogen growth?

Not for all pathogens. Although many pathogens are inhibited by refrigeration temperatures, some are not. For example, Listeria monocytogenes can multiply during refrigerated storage.

There is a lot of talk about food safety in the home. But don’t most outbreaks happen in restaurants?

The same food handling practices that pose a risk in the restaurant environment also pose a risk in an individual home. However, an outbreak of foodborne illness linked to a restaurant is far more likely to be identified because the number of victims is greater. Especially in the case of minor illness for which many people do not require medical treatment, the incidence of illness from foods prepared and eaten at home is extremely difficult to measure.

Is produce safer than meat from a microbiological food safety perspective?

Not necessarily. Although most raw meats should be adequately cooked for safety, fresh produce also may be contaminated with pathogens. When this produce is consumed raw, it represents a significant food safety concern. Efforts to minimize contamination of produce focus on good agricultural practices and proper procedures during harvest, storage, and distribution. Rinsing, scrubbing, and sometimes peeling fresh produce also helps enhance food safety.

Are organic foods safer from a microbiological perspective?

This is a controversial issue. In fact, certain agricultural practices typically used in organic farming—especially using manure as a fertilizer—have the potential to contaminate foods with pathogens. In addition, organic farming practices generally prohibit the use of some microbial controls, such as certain chemical sanitizers and irradiation, that could be used to reduce the risk of foodborne pathogens.

Do imported foods have more pathogens than domestically produced foods?

They might, but they might not. The real issue with imported foods is two-fold: (1) we have less information about and ability to influence the growing and handling conditions for imported foods, and (2) the imported foods may contain different pathogens than domestically produced foods because of the different growing regions and conditions. Global sourcing provides a wider selection for consumers that improves nutrition worldwide. However, in terms of disease control programs, globalization minimizes traditional geographic barriers to emerging as well as traditional pathogens. Consistent, widespread application of science-based food safety systems must be encouraged for international trade.

Do antibiotics in animal feed cause more virulent pathogens?

Like any use of antibiotics in medicine or production agriculture, the addition of antibiotics to animal feed has the potential to promote the development and dissemination of antibiotic- resistant microorganisms. In addition, antibiotics, like other environmental stresses, may accelerate the rate of microbial mutations.

Does intensive agriculture have a negative impact on food safety?

Intensive agriculture methods are theorized to aid in the potential development and dissemination of more virulent pathogens. Close contact facilitates the spread of pathogens to a larger number of animals. Further, large numbers of animals in close contact may provide microorganisms with greater opportunity to exchange genetic material with other microorganisms. However, some intensive agriculture is highly controlled to prevent disease. The impact on public health is difficult to quantify.

Recognizing that food safety is a fundamental and continuing issue, the Institute of Food Technologists commissioned an expert panel to review the available scientific literature related to emerging microbiological food safety issues. The panel’s report is divided into seven sections: Introduction, Pathogenicity, Human Hosts, Microbial Ecology, Application of Science to Food Safety Management, Next Steps, and Conclusions. Copies of the report are available at www.ift.org. Founded in 1939, IFT is a 28,000 member nonprofit scientific society for food science and technology.