As we mentioned last week, produce safety risks can come in many different forms on a farm. Farmers must be aware of these risks and work hard to minimize them. With knowledge, education, and action, a farmer can take easy steps to reduce risk on their operation.

This week, we will discuss one of the most common forms of pathogenic produce safety risks: bacteria.

Bacteria are microorganisms that can multiply both inside and outside of a host and can multiply rapidly given the right conditions. Examples of common bacteria in produce include salmonella, toxigenic E. coli, shigella, and listeria monocytogenes. Illnesses caused by these bacteria can be severe or even deadly. Those with compromised immune systems, such as children or the elderly, are at an even higher risk for serious illness. That’s why it is vital that growers understand how illness-causing bacteria grow and the best strategies for reducing their spread.

Many fruits and vegetables have folds or creases, such as lettuce, where if bacteria get on the produce it can linger and multiply. E. coli bacteria caused the recent romaine lettuce outbreak, and while it’s still unclear how E. coli ended up on the lettuce, it is clear it was able to linger once there.  Using a Good Agricultural Practice, or a GAP, like adding a sanitizer to your wash water can reduce the risk of bacteria by killing off bacteria that get dislodged from the produce during wash and keeping bacteria from spreading to other produce in the water. Each sanitizer has different conditions at which it is most effective, so it is important when using a sanitizer to monitor and maintain those conditions.

Bacteria survive and grow when certain conditions are met. GAPs are designed to reduce those conditions and minimize the produce safety risk. Below is a breakdown of the conditions for bacterial growth and survival and some strategies for reducing growth:

Food: Bacteria need nutrients such as sugars, starch, proteins, etc. to continue growing. Removal of nutrient build-up through proper sanitation and the use of clean breaks can minimize this growth. The University of Florida is a great resource for more information on clean breaks.

Acidity: Most pathogens thrive at pH 6.6-7.5 but can grow at slightly acidic conditions (4.5-7.7). As we mentioned above, adding a food-grade sanitizer to your post-harvest water such as chlorine or peroxyacetic acid (PAA) can help reduce the growth of pathogens. These sanitizers effectiveness can be affected by pH as well so frequent pH testing of your post-harvest water is recommended.

Time: In the right conditions, bacteria can multiply once every 20 minutes! To reduce risks, move produce quickly out of the field to a packhouse or fridge. This can decrease the amount of time bacteria has to grow.

Temperature: Cooling produce can slow bacterial growth while cooking it will kill off most bacteria present. Most pathogens grow best between 41°F and 135°F. For fresh produce keeping it cool and maintaining the cold chain is the best way to deter or slow bacterial growth. Some pathogens, such as Listeria monocytogenes, can multiply in cooler temperatures though. Learn which bacterial outbreaks are most commonly associated with your crop and understand which temperatures those pathogens thrive to ensure you’re accounting for those risks.

Oxygen: Many pathogens are aerobic, meaning they need oxygen to grow. Growers might consider switching to packaging that reduces oxygen presence or incorporating oxygen absorbers in their shipping crates or boxes. An added benefit of these methods is they will reduce the growth of organisms that can lead to spoilage of produce.

Moisture: Like other life forms, bacteria need water to survive. Standing water or moisture clinging to produce can be the ideal environment for bacteria to thrive. Always allow produce to dry before storing, such as spin-drying leafy greens. Thinking about packhouse design that will reduce pooling water can also reduce risk.

Keeping these conditions front of mind and using GAPs to reduce the likelihood or growth of bacteria will help farmers keep their produce safe for consumers.

Still have questions about bacteria? Have suggestions for other ways you reduce risks from bacteria on your operation? Let us know in the comment section below. Stay tuned for next week, where we will discuss another harmful pathogen: viruses!

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