Food Quality & Safety
Image 1: Scanning electron microscopy image of E. coli O157:H7 cells attached to ­plastic material.
Sanitation | Sanitizing

Biofilms on Equipment

• By Christopher A. Baker and Steven C. Ricke, PhD

In the past decade, several outbreaks related to fresh produce have occurred, and at least some of these factors that have contributed these outbreaks remain to be determined. Did any of these outbreaks result from the container the food was shipped in or the processing equipment that it came in contact with? Although detection platforms (real-time polymerase chain reaction, or PCR, and whole genome sequencing, among others) rapidly advance, it is unrealistic to analyze each factor that may have been associated with an outbreak. Food safety affiliates are left with many unknowns from these outbreaks, and the alternative approach to determine the level of risk posed by each factor requires sound scientific research.

Image 1: Scanning electron microscopy image of E. coli O157:H7 cells attached to ­plastic material.

Image 1: Scanning electron microscopy image of E. coli O157:H7 cells attached to ­plastic material.
Image Credit: Elizabeth M. Martin, PhD, University of Arkansas

The Changing Factors

Assessing the level and sources of risk remains a moving target. Many times there is a perfect storm that leads to produce contamination and a subsequent outbreak. Which factors contribute to this perfect storm? This is yet to be determined. Research for the correct answer will likely be warranted in years to come. Likewise, as our society continues to progress through sustainability measures, all of the factors that may lead to contamination from farm to fork should be assessed within the framework of limiting waste and becoming more sustainable. Balancing sustainability with food safety control measures remains a complex multifaceted challenge. For example, water use for sanitization of containers, processing facilities, etc. must be considered along with water conservation. Although recent research from National Oceanic and Atmospheric Administration suggests that droughts in California are primarily due to natural oceanic and atmospheric patterns, human water use practices may contribute to the likelihood of droughts. Therefore, processing facilities in the future may not have the luxury of excessive water-based washes to dilute for routine cleaning of equipment and reusable packaging containers and other services.

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The game may change considerably in the coming years with regard to how industry sanitizes its equipment, and it seems that regulations will need to be adjusted in the case of a limited water supply. However, water and sanitizer application use is critical for achieving sufficient cleaning. Biofilms (and general bacterial buildup) are notorious for hanging on for dear life, proving removal efforts insufficient. Finding biofilm on surfaces such as processing equipment and shipping containers is threatening since they are likely to be continually reused, and can contaminate every product that it comes into contact with, thus creating a production line of contaminated fresh produce.

The Pathogens

Research is primarily focused on biofilms, but single attached cells could potentially contaminate a product, especially if these cells proliferate into a sufficient population. Fresh produce is typically uncooked before consumption, and depending on the consumer as well as the pathogen on the produce, only a few cells could lead to illness.

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For instance, Shiga toxin-producing Escherichia coli (STEC) are notorious for leading to illness following exposure to a small number of cells, and based on past outbreaks, it seems evident that illnesses associated with ready-to-eat and fresh produce will likely continue. E. coli O157:H7 is infamous for the 1993 outbreak in the Northwest region of the U.S. This outbreak was linked to several deaths, and resulted from undercooking ground beef patties that were contaminated with E. coli O157:H7. The fact of the matter is that even if food products are contaminated with harmful bacteria, proper cooking and preparation practices (reaching an acceptable internal temperature and avoiding cross-contamination) will eliminate these pathogens, and foods can be consumed safely. Unfortunately, ready-to-eat raw foods such as fresh produce are seldom cooked before consumption, so the health risks associated with these products is much greater. Many Americans are making efforts to consume higher amounts of raw fruits and vegetables for a healthier diet, and the potential for illnesses is a major drawback to these uncooked products.

The Research

The ability of foodborne pathogens to attach to as well as persist on surfaces is a real concern. For example, a recently published manuscript in the Journal of Food Research suggests that attached cells may be able to withstand some of the sanitizers used in industry for cleaning procedures. One-inch squared coupons (plastic material) were exposed to a cocktail of Salmonella cells for a three-day period, rinsed thoroughly with water, treated with a variety of sanitizers, and subsequently swabbed in a way that simulates scrubbing for equipment cleaning procedures. Several treatments were evaluated, and although these treatments reduced levels of bacterial cells, none were sufficient to completely remove the attached Salmonella cells.

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