Preventing E. coli From Garden to Plate

Imagine you're strolling down the aisle of your local grocery store, and you spot a bin full of vibrant greens, fresh from the farm. You might assume that these leafy vegetables are free from harmful bacteria and safe to eat. However, a closer look at the source of pre-harvest contamination reveals a different story. In recent years, there has been an alarming increase in outbreaks of foodborne illnesses related to produce. Bacteria like Escherichia coli, Salmonella, Listeria monocytogenes, Shigella, and Cyclospora have been linked to these outbreaks, causing serious health concerns. Some of these bacteria occur naturally in soil, but others can contaminate produce through manure, irrigation water, wash water, or contact with animals. According to Mitzi Baum, CEO of Stop Foodborne Illness, leafy greens like lettuce and spinach are at higher risk of E. coli contamination due to their growth method. Since these vegetables are grown in soil, which can be exposed to animal feces or contaminated water, the risk of contamination is increased, especially from irrigation water near animal production facilities. Sprouts and green leafy vegetables are the vegetables most associated with E. coli, and outbreaks have been reported with significant hospitalization rates.

Preventing E. coli From Garden to Plate.docx - Goo

Selected E. coli 0157 : H7 (otherwise noted) outbreaks associated with vegetables reported by the CDC. 

Pre-harvest E.coli contamination 

The leading cause of pre-harvest contamination in vegetables like lettuce and leafy greens is soil, which can harbor E. coli bacteria for up to 25 weeks. The risk is further exacerbated by the proximity of crop fields to animal production areas, where domestic animals and wildlife can deposit their feces and spread pathogenic bacteria. 

It's not just animals that pose a threat to the safety of our food; insects, too, can be carriers of E. coli. Flies have been shown to transfer bacteria from contaminated sources to plant leaves or fruits. Even the seasons can impact the prevalence of E. coli, with contamination in cilantro and parsley spiking in the fall. 

But the problem doesn't stop there. Reports indicate that contaminated irrigation water can also spread E. coli to crops, particularly during heavy rainfall. The risk of transmission can vary depending on the irrigation system used, with drip irrigation posing a lower risk than overhead sprinklers. 

And let's not forget about the human factor. Workers who handle and harvest crops can also contribute to pre-harvest contamination if they lack access to basic hygiene facilities like latrines and handwashing stations. 

Post-harvest E.coli contamination 

Postharvest E. coli contamination can occur where vegetables such as fresh spinach, and raw clover sprouts have been found to contain high levels of E. coli. The contamination can be caused by direct contact with pathogens or due to their multiplication during postharvest procedures. The confirmation of E. coli during postharvest packing is a red flag, indicating potential fecal contamination and the presence of enteric pathogens. 

Water plays a significant role in postharvest procedures such as washing, chilling, spraying, and shipping ice. The use of contaminated water during these procedures can contribute to E. coli contamination in vegetables. Washing is essential to remove soil and debris, but if the water is contaminated, it can serve as a source of E. coli transmission. Hydrocoolers can also lead to contamination, and the lack of cooling during storage can increase the risk of E. coli growth. 

Cross-contamination can also occur during the preparation of vegetables in restaurants or home kitchens. Food handlers' hands can spread E. coli if they handle raw meat or poultry before preparing vegetables, leading to the establishment of pathogens. Even the simple act of cutting vegetables during salad preparation has been linked to bacterial growth, with fresh-cut produce used in salads posing a potential risk. Studies have also highlighted the risk of acquiring an ETEC (Enterotoxigenic E.coli) infection when chopped vegetables are used in the preparation and consumption of Mexican salsa. 

Preharvest and Postharvest Preventive Measures for Fresh Produce 

To prevent E. coli contamination in fresh produce, there are several measures that can be taken: 

Preharvest measures: 

  • Stabilize fertilizers: The use of compost and other fertilizers should be stabilized to reduce the level of pathogenic microorganisms. 
  • Avoid untreated human sewage: It's crucial to avoid using untreated human sewage, except it meets the specifications for the use of biosolids. 
  • Quality of water for irrigation: The quality of water for irrigation is also critical in preventing microbial contamination. 

Postharvest measures: 

  • Proper handling: Proper handling of fresh produce is necessary to reduce contamination during postharvest procedures. 
  • Storage: Proper storage techniques, such as maintaining adequate cooling, are important to prevent E. coli growth.
  • Transportation: Adequate washing, disinfection, and the application of good agricultural practices are recommended during transportation to avoid contamination.
  • Cleaning: Cleaning and disinfection of equipment and surfaces used in handling fresh produce are necessary to prevent cross-contamination.
  • Personal hygiene: Food workers should improve their personal hygiene and follow standard procedures for handling food. 
  • Environmental monitoring: rapid pathogen detection methods. Another important measure to prevent E.coli contamination is environment monitoring through rapid pathogen detection methods. Rapid pathogen screening can detect the presence of E. coli on food surfaces before it causes an outbreak. For example, the NEMIS N-LightTM E. coli screening test is suitable for use in food processing areas and equipment as part of an environmental monitoring program for testing process water and other liquid samples. By utilizing this technology, food manufacturers can proactively identify and address potential sources of contamination to prevent the spread of harmful pathogens like E. coli in their products. 
  • Use of sanitizing agents: The use of sanitizing agents, such as chlorine, peroxyacetic acid, and ozone, has been evaluated for their efficacy against pathogenic and spoilage microorganisms. Sodium persulfate activated by ferrous sulfate and sodium hydroxide has also been found to be effective against E. coli O157: H7. 
  • Modified Atmosphere Packaging (MAP): The use of MAP of fresh fruits and vegetables results in an extended shelf life by utilizing an internal package atmosphere other than air in a hermetically sealed package. 
  • Education: It's also important to maintain a good level of education on the appropriate use of sanitizing agents and the principles of food hygiene and safety, as recommended by the Food Safety Modernization Act (FMSA) for fresh products. 

In conclusion 

In conclusion, preventing E. coli contamination in fresh produce requires a comprehensive approach that spans from preharvest to postharvest measures. From stabilizing fertilizers and avoiding untreated sewage in preharvest to proper handling, transportation, and cleaning in postharvest, there are many steps that can be taken to reduce the risk of contamination. The use of rapid pathogen detection methods and advanced technologies such as NEMIS N-LightTM can also help monitor and control factors such as hand hygiene, incoming materials, and the effectiveness of sterilization steps in food processing. It is crucial to maintain a good level of education on the appropriate use of sanitizing agents and the principles of food hygiene and safety. By adhering to these measures, the risk of E. coli contamination in fresh produce can be minimized, resulting in a safe and healthy diet for consumers. 

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