Foodborne disease outbreaks associated with fresh produce irrigated with contaminated water are a constant threat to consumer health. In this study, the impact of irrigation water on product safety from different food production systems (commercial to small-scale faming and homestead gardens) was assessed.
Hygiene indicators (total coliforms, Escherichia coli), and selected foodborne pathogens (Salmonella spp., Listeria monocytogenes, and Escherichia coli O157:H7) of water and leafy green vegetables were analyzed. Microbiological parameters of all irrigation water (except borehole) exceeded maximum limits set by the Department of Water Affairs for safe irrigation water. Microbial parameters for leafy greens ranged from 2.94 to 4.31 log CFU/g (aerobic plate counts) and 1 to 5.27 log MPN/100g (total coliforms and E. coli). Salmonella and E. coli O157:H7 were not detected in all samples tested but L. monocytogenes was present in irrigation water (commercial and small-scale farm, and homestead gardens).
This study highlights the potential riskiness of using polluted water for crop production in different agricultural settings.
Assessment of irrigation water quality and microbiological safety of leafy greens in different production systems
Journal of Food Safety, 2 November 2016, DOI: 10.1111/jfs.12324
We used whole-genome sequencing to characterize a set of VT2f-producing E. coli strains from human patients with diarrhea or HUS and from healthy pigeons. We describe a phage conveying the vtx2f genes and provide evidence that the strains causing milder diarrheal disease may be transmitted to humans from pigeons.
The strains causing HUS could derive from VT2f phage acquisition by E. coli strains with a virulence genes asset resembling that of typical HUS-associated verotoxigenic E. coli.
Whole-genome characterization and strain comparison of VT2f-producing Escherichia coli causing hemolytic uremic syndrome
Jake Shama of the Mitchell Republic reports that watching 6-year-old Eagan Hudson playing darts, eating candy and running around the Tyndall Community Center on Saturday, one would never guess he’d been released from the hospital just one month earlier.
Bon Homme County residents and others from as far away as Wisconsin filled the community center and raised more than $50,000 during the benefit for Eagan and his family, according to James Torsney, one of the event’s organizers.
The benefit was held to help pay medical bills, which the family incurred when Eagan was taken to Sanford Children’s Hospital in Sioux Falls for treatment of hemolytic uremic syndrome (HUS), believed to be caused by an E. coli infection.
“It was really hard, and I had to go through lots of pain. It was not fun,” said Eagan, of Tyndall. “I just had all those doctors help me, and everything went good.”
Eagan and his brother, Kalem, 4, contracted E. coli in the middle of September. Kalem’s illness was resolved fairly quickly, his parents said, but Eagan’s condition didn’t improve. By Oct. 6, platelet and kidney tests raised red flags, and doctors sent Eagan to Sioux Falls for treatment.
Three days later, Eagan suffered a stroke, which temporarily prevented him from moving his right arm and leg, and he started having seizures the following morning.
Doctors had medication flown in from six hours away, and Eagan was sedated for 10 days, during which he was given nonstop dialysis treatments.
Ashley Nickle of The Packer reports that Bruce Taylor, CEO and founder of Salinas, Calif.-based Taylor Farms, emphatically denounced the study.
“We find the artificial conditions created by this study to be ridiculous,” Taylor said in an e-mail. “Producers of bagged salads do not have ‘juice’ in the salad bag, and producers take painstaking steps to avoid the introduction of salmonella or any other pathogen.”
The conclusion regarding refrigeration was the only notable one in the study, said Trevor Suslow, a member of the technical committee of the Center for Produce Safety. Scientists would expect salmonella to be able to survive at the temperature recorded in the study but would not expect it to grow, he said.
“People will definitely be trying to reproduce their results as far as growth under refrigeration temperature for salmonella,” Suslow said. “That’s, for me, the key issue.”
Suslow, an extension research specialist at the University of California-Davis, said it is already known that a bagged salad is an environment in which salmonella can have the nutrients it needs to grow, which is why the industry has focused so intently on ensuring no pathogens make it into bags into the first place.
Drew McDonald, vice president of quality, food safety and regulatory affairs at Salinas-based Church Brothers Farms, said in an e-mail that, although the researchers did some things well, he also had some issues with the study.
“From my read, the study essentially grew salmonella in juices extracted from actual bagged salads in a mixture of sterile water,” McDonald said. “The issue is that in the ‘real’ world the salmonella has to come from somewhere (the surface of the leaf for example) but along with this would be many other microorganisms. That they were able to grow salmonella under these forced, artificial conditions without any competition from other organisms is not surprising.”
Along with the growth conditions, the washed status of the lettuce also gave McDonald pause.
“From my understanding, (the) project used ‘bagged salad,’” McDonald said. “I am assuming this means it was already washed. The fact that they added salad juice and salmonella after it had already been bagged and washed really just shows how important it is to not cross-contaminate cleaned product.”
The researchers, as a result of their findings, suggested people eat bagged salads as soon as possible after purchase to minimize risk. They wrote in a question-and-answer supplement to the release that they no longer keep their bagged salads in the refrigerator longer than one day.
“Ridiculous recommendation,” Taylor said in his e-mail. “For 30 years consumers have enjoyed hundreds of millions of bagged salads weekly with great benefit to their health and wellbeing.”
Jennifer McEntire, vice president of food safety and technology at United Fresh Produce Association, also disagreed with the recommendation.
“People should always follow the instructions, including best-by dates, on packages, mainly so that they experience the best quality product,” McEntire said in an e-mail. “People shouldn’t be afraid to keep salad in their refrigerators for the full duration of the shelf life.”
She may mean use-by dates.
Suslow described the study as another piece of the puzzle in trying to find long-term solutions for food safety issues, but he was not impressed by it.
“Sort of generating a lot of additional concern and fear without any real basis for changing what (is) sort of standard practice isn’t necessarily helpful,” Suslow said. “Could hurt the category, but probably no more so than other things such as those instances when there are outbreaks or recalls.
“I think consumers understand that there’s no such thing as zero risk,” Suslow said (smartest thing anyone said in this story). “They understand and appreciate the convenience of packaged salads with multiple ingredients with very healthy mixed leafy greens, and that’s how the category has grown.”
In November 1996, over 400 fell ill and 21 were killed in Scotland by E. coli O157:H7 found in deli meats produced by family butchers John Barr & Son. The Butcher of Scotland, who had been in business for 28 years and was previously awarded the title of Scottish Butcher of the Year, was using the same knives to handle raw and cooked meat.
A memo at the time, unearthed by The Herald shows what many suspected: that the interests of the food and agriculture industries were given higher priority than public health.
Then Scottish Office health minister, James Douglas-Hamilton, wrote on Dec. 5, 1996 to Sir Russell Hillhouse, the under-secretary of state at the Scottish Office that, “The key issue to be addressed is that when there is an outbreak of infectious disease whether the public health interest should over-ride the food industry and agricultural interests. I believe the public health interest should be paramount, but it was not seen to do so in this case.”
The aptly named agriculture minister, Douglas Hogg, argued E. coli was a “Scottish issue” and that licensing should only be in Scotland.
A memo to Secretary of State for Scotland Michael Forsyth, on March 19, 1997, noted: “The Cabinet Office and No 10 were not impressed by Mr Hogg’s idea.”
Ross Thompson of the Daily Record reports that 20 years later, a Wishaw Old Parish Church member believes the heart was ripped from the congregation in the wake of the crippling E. coli tragedy.
Wishaw Old Parish Church session clerk Tom Donaldson was served the same meal as 10 others who lost their lives from the killer bug when infected meat, from John Barr’s Butchers, was served at an annual church lunch.
This week marks 20 years since the outbreak claimed its first victim, 80-year-old Harry Shaw.
Over the next few weeks, 20 others died and hundreds more were infected in what is still the world’s worst E. coli outbreak.
This week, Tom reflected on the horrific events two decades on.
He said: “Many of our members and office-bearers still carry the sad memories of that time.
“The heart was torn from the church by the loss of so many members.
“We lost eight members, including three valued elders.
“We held the same meal for over 10 years. For a lot of the people going, it was a chance to get out of the house and see people they hadn’t seen for a while.
“I had the same meal as everyone else but, thankfully, I didn’t have any symptoms. When we heard that people were unwell and then that people had died we couldn’t believe it.
“It was really heart-breaking.”
Over the next few weeks, the world’s media converged on Wishaw to cover the ongoing tragedy.
One man who carried the burden more than most was church minister Rev James Davidson.
Indeed, after burying three of his congregation, Rev Davidson admitted it had been the worst week of his life.
Tom added: “The minister carried the heavy burden as pastor; not only by conducting so many funerals in such a short period but also having to continue to minister to the congregation Sunday by Sunday.
“In one week he had to carry out three funerals. He was heart-broken.
“He really needed more help than he got because not only was he doing those funerals but he was also going to the hospital to visit the sick as well.
“The local media, like the Wishaw Press, and the guys who worked for the Scottish television channels were very respectful. But there was the other side where others would confront the minister and other office- bearers, at their homes and at the church for a comment.
“For quite a few years we had to deal with being ‘that E. coli church’ and people still remember that.”
The research is cool, but to me it culminates 16 years of Chapman becoming a better researcher.
I had a hand in the idea for the paper, but Chapman and his team did all the work.
I edited some stuf.
I was reminded last night of all the youthful energy me, and Chapman and Blaine and Lisa and Brae and Katie and Sarah and the reintroduced Carol – had when we did the bulk of our creative work.
Sorta like the Stones 68-72.
And yet that was the most turmoil in my life, as I went through a painful divorce, separation from kids, an interesting girlfriend and finally meeting Amy a few years later.
My line is graduate students should be able to bail their supervisor out of jail or drive me to the airport when (I) threatened with arrest.
Sorta like the Stones 68-72.
This is Chapman’s moment to shine, and although barfblog.com was named the number 1 food safety blog by someone pushing something today, it don’t matter much.
Often Chapman and I will send an e-mail to each other about some obscure reference in a post, with the comment, we only write for each other.
And the over 75,000 direct subscribers in over 70 countries.
Well done Chapman et al., couldn’t be prouder.
You too Blaine.
Assessment of risk communication about undercooked hamburgers by restaurant servers
Ellen M. Thomas, RTI International; Andrew Binder, Anne McLaughlin, Lee-Ann Jaykus, Dana Hanson, and Benjamin Chapman, North Carolina State University; and Doug Powell, powellfoodsafety.com
Journal of Food Protection
DOI: 10.4315/0362-028X.JFP-16-065
According to the U.S. Food and Drug Administration 2013 Model Food Code, it is the duty of a food establishment to disclose and remind consumers of risk when ordering undercooked food such as ground beef. The purpose of this study was to explore actual risk communication activities of food establishment servers. Secret shoppers visited restaurants (n=265) in seven geographic locations across the U.S., ordered medium rare burgers, and collected and coded risk information from chain and independent restaurant menus and from server responses. The majority of servers reported an unreliable method of doneness (77%) or other incorrect information (66%) related to burger doneness and safety. These results indicate major gaps in server knowledge and risk communication, and the current risk communication language in the Model Food Code does not sufficiently fill these gaps. Furthermore, should servers even be acting as risk communicators? There are numerous challenges associated with this practice including high turnover rates, limited education, and the high stress environment based on pleasing a customer. If it is determined that servers should be risk communicators, food establishment staff should be adequately equipped with consumer advisory messages that are accurate, audience-appropriate, and delivered in a professional manner so as to help their customers make more informed food safety decisions.
Markham-based Michidean Limited (that’s in Ontario, which is in Canada) is voluntarily recalling the following products:
16320 Michidean JA PATTY Extra Spicy Beef (frozen unbaked)
16320 Michidean JA PATTY Extra Spicy Beef (baked)
Customers should not eat the recalled products, said a release from York Region.
Food contaminated with E. coli O157:H7 may not look or smell spoiled but can still make you sick, noted the release. Symptoms can include nausea, vomiting, mild to severe abdominal cramps and watery to bloody diarrhea.
So far, there are no reports of any illnesses related to the beef patties.
In 2013, Emma Heidish spent a month overcoming a potentially deadly form of kidney disease which cause her kidneys to shut down and required surgery and near constant dialysis.
On Tuesday, a Hennepin County jury found the owners of the farm where she got E. coli, Dehn’s Pumpkins in Dayton, negligent for not taking steps to prevent their animals from transmitting diseases and awarded Emma $7.5 million.
The bulk of the money is for future medical bills and pain and suffering.
“It is one of the largest verdicts in the country for an E. coli outbreak for a condition like this one and its one of the largest involving a petting zoo case,” Emma’s attorney, Fred Pritzker, said. “The people who run the pumpkin patch are decent people. It’s not that they were mean spirited. But, what they didn’t know caused a great deal of pain and suffering for my clients.”
Since the outbreak, the popular pumpkin patch no longer operates a petting zoo, but Pritzker sais animal attractions like it are not regulated or inspected.
His firm will push for a new law, named after Emma, requiring petting zoos to follow safety precautions, like having hand washing stations nearby to help prevent the spread of the disease.
“There have been 150 to 200 cases of outbreaks involving animals in public settings in the last 15 years, Pritzker said
Pritzker says Emma probably won’t see all the money because the farm’s insurance doesn’t have that much coverage.
Q2. Under this final rule, will the product need to be labeled with the specific method of mechanical tenderization used to prepare the product?
No, the label need not include the specific type of mechanical tenderization used. To provide flexibility, FSIS is allowing the phrase ‘‘mechanically tenderized’’ to be used as the descriptive designation on any type of mechanically tenderized product. In addition, in lieu of “mechanically tenderized,” such product may be labeled as ‘‘needle tenderized’’ or ‘‘blade tenderized,’’ as applicable.
Q3. Can “needle injected” be used as the descriptive designation on the labels of raw or partially cooked beef products that have been mechanically tenderized?
No, needle injected may not be used as the descriptive designation. The terms “needle tenderized” or “mechanically tenderized” must be used as the descriptive designation for needle tenderized raw or partially cooked beef products and the terms “mechanically tenderized” or “blade tenderized” must be used as the descriptive designation for raw or partially cooked blade tenderized beef products.
Q4. Are the descriptive designations “mechanically tenderized,” “blade tenderized,” or “needle tenderized” only required on raw or partially cooked beef products?
Yes, unless the product is destined to be fully cooked or to receive another full lethality
treatment at an official establishment, such product must be labeled accordingly.
Q5. Do the new labeling requirements apply to mechanically tenderized pork, lamb, or goat products?
No. The rule applies only to raw or partially cooked beef products that have been mechanically tenderized.
Q6. Can establishments put both mechanically tenderized beef products and non- mechanically tenderized beef products in the same immediate container and label it with the descriptive designation “mechanically tenderized?”
No. To label product as “mechanically tenderized” when it was not would be false and misleading.
Q7. If we sell mechanically tenderized raw or partially cooked beef or veal products in protective coverings, must the protective coverings meet the mechanical tenderization labeling requirements when the immediate container of this product is labeled “For Institutional Use Only?”
No. Under 9 CFR 317.1(a)(1), protective coverings should not bear any mandatory labeling information.” In this case, the immediate container, which also serves as the shipping container, is required to be labeled with the descriptive designation and bear validated cooking instructions and all other applicable labeling features.
Q8. Is beef cubed steak is subject to the new labeling requirements?
No, this regulation will not apply to raw or partially cooked beef products that have been cubed. The regulation is specific to needle and blade tenderized beef products. FSIS stated in the final rule:
The descriptive designation will only apply to raw or partially cooked beef products that have been needle tenderized or blade-tenderized, including beef products injected with marinade or solution. Other tenderization methods, such as pounding and cubing, change the appearance of the product, putting consumers on notice that the product is not intact. Moreover, most establishments already label cubed products as such. (80 FR 28157)
Q9. Must the labels for raw or partially cooked mechanically tenderized beef products be submitted to the FSIS Labeling and Program Delivery Staff (LPDS) for approval?
No. The descriptive designations, “mechanically tenderized,” “blade tenderized,” and “needle tenderized” are not considered special statements or claims under 9 CFR 412.1(c). Therefore, as stated in the final rule, simply adding the descriptive designation and validated cooking instructions to a label would not require LPDS approval, given the label is otherwise in accordance with FSIS’s regulations.
Q10. Do the new labeling requirements apply to raw or partially cooked mechanically tenderized beef products that are produced at establishments that use a validated intervention during the production of such products?
Yes, the new labeling requirements would apply to products treated with a validated antimicrobial intervention, unless the establishment applies a lethality treatment that achieves a 5-log reduction in pathogens. Mechanically tenderized beef product treated at an official establishment with an intervention or process, including HPP, that has been validated to achieve at least a 5-log reduction for Salmonella and Shiga Toxin-producing E. coli (STEC) organisms (including E. coli 0157:H7) would not be subject to the requirements in this final rule because it has received a full lethality treatment. (See 80 FR 28153)
Q11. Do the new labeling requirements apply to mechanically tenderized beef products labeled or prepared at retail stores?
Yes, the new labeling requirements would apply to raw or partially cooked mechanically tenderized beef products produced, packaged, and labeled at a retail store.
Cooking Instructions
Q12. Is there compliance guidance available on validating cooking instructions for mechanically tenderized beef products?
Yes, at:
FSIS Compliance Guideline for Validating Cooking Instructions for Mechanically Tenderized Beef Products
Q13. Where can I find scientific studies on validated cooking instructions?
Attachment 1 of the above FSIS Compliance Guideline for Validating Cooking Instructions for Mechanically Tenderized Beef Products contains a summary of published scientific support for cooking instructions.
Q14. Do the new labeling requirements apply to raw or partially cooked mechanically tenderized beef products that are too thin to practically measure their internal temperature using a food thermometer?
No, the new labeling requirements do not apply to raw or partially cooked mechanically tenderized (including through injection with a solution) beef products that are too thin to measure their internal temperature using a food thermometer, such as beef bacon or carne asada. FSIS does not intend to enforce the requirements for these products because they are customarily prepared in a manner that is sufficient to destroy pathogenic bacteria.
Note that the thickness of many food thermometers used by consumers is approximately 1/8,” making it difficult to measure the end product temperature of products 1/8” thick or less through use of a thermometer.
Q15. Where on the label of raw or partially cooked mechanically tenderized beef products can the validated cooking instructions appear?
Validated cooking instructions must appear on the immediate containers of all raw or partially cooked mechanically tenderized beef products destined for household consumers, hotels, restaurants, or similar institutions. These instructions can appear anywhere on the product label.
Mechanically Tenderized Beef With Solutions
Q16. Must the label of a raw or partially cooked mechanically tenderized beef product that contains added solution also declare the percentage of added solution?
Yes. However, there are different options for declaring the total amount of solution added. See 9 CFR 317.2(e)(2).
Q17. Do the new labeling requirements apply to raw or partially cooked beef products that have been marinated in a tumbler or vacuum tumbled?
The rule only applies to raw or partially cooked beef products that have been mechanically tenderized by needle or blade. This rule does not apply to other processes, such as tumbling or vacuum tumbling, unless the product is also mechanically tenderized by needle or blade.
That’s my response to people who ask about the proportionally high rates of foodborne illness in lettuce and other leafy greens eaten raw.
I like spinach – in a lasagna or stir-fry – but not raw.
Raw is risky.
There’s a bunch of new findings on foodborne pathogens and leafy greens which are summarized below.
In the sphere of public conversation, it is notable the Leafy Greens Marketing Agreement, the group formed after the 2006 E. coli-in-spinach outbreak that killed four and sickened at least 200 in the U.S. – has been once again silent on any research or outbreaks that associate risk with greens.
The scientists have discovered that juices released from damaged leaves also had the effect of enhancing the virulence of the pathogen, potentially increasing its ability to cause infection in the consumer.
The research is led by Dr Primrose Freestone of the University’s Department of Infection, Immunity and Inflammation and PhD student Giannis Koukkidis, who has been funded by a Biotechnology and Biological Sciences Research Council (BBSRC) i-case Studentship.
Their research investigates novel methods of preventing food poisoning pathogens from attaching to the surface of salad leaves to help producers improve food safety for consumers.
This latest study, published in Applied and Environmental Microbiology, found that juices from damaged leaves in bagged spinach and mixed salad increased Salmonella pathogen growth 2400-fold over a control group and also enhanced their adherence to surfaces and overall virulence, or capacity to cause disease.
Dr Freestone said: “Salad leaves are cut during harvesting and we found that even microliters of the juices (less than 1/200th of a teaspoon) which leach from the cut-ends of the leaves enabled Salmonella to grow in water, even when it was refrigerated. These juices also helped the Salmonella to attach itself to the salad leaves so strongly that vigorous washing could not remove the bacteria, and even enabled the pathogen to attach to the salad bag container.
“This strongly emphasizes the need for salad leaf growers to maintain high food safety standards as even a few Salmonella cells in a salad bag at the time of purchase could become many thousands by the time a bag of salad leaves reaches its use by date, even if kept refrigerated. Even small traces of juices released from damaged leaves can make the pathogen grow better and become more able to cause disease.
“It also serves as a reminder to consume a bagged salad as soon as possible after it is opened. We found that once opened, the bacteria naturally present on the leaves also grew much faster even when kept cold in the fridge.
“This research did not look for evidence of Salmonella in bagged salads. Instead, it examined how Salmonella grows on salad leaves when they are damaged.”
Leafy green and other salad vegetables are an important part of a healthy diet, providing vitamins, minerals, and dietary fiber. Ready to eat prepared salads are particularly popular, are widely consumed and so of significant economic importance. Over recent years there has however been a number of outbreaks associated with fresh salad produce contaminated with Salmonella and E. coli both in the USA and Europe.
This has triggered considerable interest in effective strategies for controls and interventions measures both in UK industry, the EU and key research funding bodies.
Despite a number of published reports on improving the microbiological safety of salad leaf production, very few studies have investigated the behavior of Salmonella once the leaves have been bagged.
Giannis said: “Anything which enhances adherence of foodborne pathogens to leaf surfaces also increases their persistence and ability to resist removal, such as during salad washing procedures. Even more worrying for those who might eat a Salmonella contaminated salad was the finding that proteins required for the virulence (capacity to cause infection) of the bacteria were increased when the Salmonella came into contact with the salad leaf juices. “Preventing enteric pathogen contamination of fresh salad produce would not only reassure consumers but will also benefit the economy due to fewer days lost through food poisoning. We are now working hard to find ways of preventing salad-based infections.”
No comment from the LGMA.
While this research may make it seem like pre-packaged salads pose a scary risk, the researchers themselves were quick to say they still eat bagged salads. But they make sure to look for packages that have appropriate use-by dates and crisp-looking leaves. They stay away from salads that have mushy, slimy-looking greens, or bags with accumulated salad juice at the bottom. And they make sure to eat the greens within one day of purchase.
“Our project does not indicate any increased risk to eating leafy salads, but it does provide a better understanding of the factors contributing to food poisoning risks,” said Freestone.
If you feel like it, you can wash greens that have already been pre-washed by manufacturers just before eating, but Freestone says this doesn’t have much of an effect on the salmonella bacteria that may already be attached or internalized by the leaves.
Foodborne disease outbreaks associated with fresh produce irrigated with contaminated water are a constant threat to consumer health. In this study, the impact of irrigation water on product safety from different food production systems (commercial to small-scale faming and homestead gardens) was assessed.
Hygiene indicators (total coliforms, Escherichia coli), and selected foodborne pathogens (Salmonella spp., Listeria monocytogenes, and Escherichia coli O157:H7) of water and leafy green vegetables were analyzed. Microbiological parameters of all irrigation water (except borehole) exceeded maximum limits set by the Department of Water Affairs for safe irrigation water. Microbial parameters for leafy greens ranged from 2.94 to 4.31 log CFU/g (aerobic plate counts) and 1 to 5.27 log MPN/100g (total coliforms and E. coli). Salmonella and E. coli O157:H7 were not detected in all samples tested but L. monocytogenes was present in irrigation water (commercial and small-scale farm, and homestead gardens).
This study highlights the potential riskiness of using polluted water for crop production in different agricultural settings.
No comment from LGMA.
Adaptive response of Listeria monocytogenes to heat, salinity and low pH, after habituation on cherry tomatoes and lettuce leaves
PLOS
Sofia V. Poimenidou, Danai-Natalia Chatzithoma, George-John Nychas, Panagiotis N. Skandamis
Pathogens found on fresh produce may encounter low temperatures, high acidity and limited nutrient availability. The aim of this study was to evaluate the effect of habituation of Listeria monocytogenes on cherry tomatoes or lettuce leaves on its subsequent response to inhibitory levels of acid, osmotic and heat stress.
Habituation was performed by inoculating lettuce coupons, whole cherry tomatoes or tryptic soy broth (TSB) with a three-strains composite of L. monocytogenes, which were further incubated at 5°C for 24 hours or 5 days. Additionally, cells grown overnight in TSB supplemented with 0.6% yeast extract (TSBYE) at 30°C were used as control cells. Following habituation, L. monocytogenes cells were harvested and exposed to: (i) pH 3.5 adjusted with lactic acid, acetic acid or hydrochloric acid (HCl), and pH 1.5 (HCl) for 6 h; (ii) 20% NaCl and (iii) 60°C for 150 s.
Results showed that tomato-habituated L. monocytogenes cells were more tolerant (P < 0.05) to acid or osmotic stress than those habituated on lettuce, and habituation on both foods resulted in more stress resistant cells than prior growth in TSB. On the contrary, the highest resistance to heat stress (P < 0.05) was exhibited by the lettuce-habituated L. monocytogenes cells followed by TSB-grown cells at 5°C for 24 h, whereas tomato-habituated cells were highly sensitized. Prolonged starvation on fresh produce (5 days vs. 24 h) increased resistance to osmotic and acid stress, but reduced thermotolerance, regardless of the pre-exposure environment (i.e., tomatoes, lettuce or TSB).
These results indicate that L. monocytogenes cells habituated on fresh produce at low temperatures might acquire resistance to subsequent antimicrobial treatments raising important food safety implications.
No comment from LGMA.
Efficacy of post-harvest rinsing and bleach disinfection of E. coli O157:H7 on spinach leaf surfaces
Attachment and detachment kinetics of Escherichia coli O157:H7 from baby spinach leaf epicuticle layers were investigated using a parallel plate flow chamber. Mass transfer rate coefficients were used to determine the impact of water chemistry and common bleach disinfection rinses on the removal and inactivation of the pathogen. Attachment mass transfer rate coefficients generally increased with ionic strength. Detachment mass transfer rate coefficients were nearly the same in KCl and AGW rinses; however, the detachment phase lasted longer in KCl than AGW (18 ± 4 min and 4 ± 2 min, respectively), indicating that the ions present during attachment play a significant role in the cells’ ability to remain attached. Specifically, increasing bleach rinse concentration by two orders of magnitude was found to increase the detachment mass transfer rate coefficient by 20 times (from 5.7 ± 0.7 × 10−11 m/s to 112.1 ± 26.8 × 10−11 m/s for 10 ppb and 1000 ppb, respectively), and up to 88 ± 4% of attached cells remained alive.
The spinach leaf texture was incorporated within a COMSOL model of disinfectant concentration gradients, which revealed nearly 15% of the leaf surface is exposed to almost 1000 times lower concentration than the bulk rinse solution.
No comment from LGMA.
Development of growth and survival models for Salmonella and Listeria monocytogenes during non-isothermal time-temperature profiles in leafy greens
Leafy greens contaminated with Salmonella enterica have been linked to large number of illnesses in many countries in recent years. Listeria monocytogenes is also a pathogen of concern for leafy greens because of its prevalence in the growing and processing environment and its ability to grow at refrigeration temperatures. Experimental data for the growth and survival of S. enterica and L. monocytogenes under different conditions and storage temperatures were retrieved from published studies. Predictive models were developed using the three-phase linear model as a primary growth model and square-root model to calculate specific growth rate (ln CFU g−1 h−1) at different temperatures (°C). The square-root model for S. enterica was calculated as μ = (0.020(Temperature+0.57))2. The square-root model for L. monocytogenes was fitted as μ = (0.023(Temperature-0.60))2. The growth-survival model for S. enterica and growth model for L. monocytogenes were validated using several dynamic time-temperature profiles during the production and supply chain of leafy greens. The models from this study will be useful for future microbial risk assessments and predictions of behavior of S. enterica and L. monocytogenes in the leafy greens production and supply chain.
No comment from LGMA.
Is there a relation between the microscopic leaf morphology and the association of Salmonella and Escherichia coli O157:H7 with iceberg lettuce leaves?
Journal of Food Protection, Number 10, October 2016, pp. 1656-1662, pp. 1784-1788(5)
I Van der Linden, M Eriksson, M Uyttendaele, F Devlieghere
To prevent contamination of fresh produce with enteric pathogens, more insight into mechanisms that may influence the association of these pathogens with fresh produce is needed.
In this study, Escherichia coli O157:H7 and Salmonella were chosen as model pathogens, and fresh cut iceberg lettuce was chosen as a model fresh produce type. The morphological structure of iceberg lettuce leaves (stomatal density and length of cell margins per leaf area) was quantified by means of leaf peels and light microscopy of leaves at different stages of development (outer, middle, and inner leaves of the crop) on both leaf sides (abaxial and adxial) and in three leaf regions (top, center, and bottom). The morphology of the top region of the leaves was distinctly different from that of the center and base, with a significantly higher stomatal density (up to five times more stomata), different cell shape, and longer cell margins (two to three times longer). Morphological differences between the same regions of the leaves at different stages of development were smaller or nonsignificant. An attachment assay with two attenuated E. coli O157:H7 strains (84-24h11-GFP and BRMSID 188 GFP) and two Salmonella strains (serovars Thompson and Typhimurium) was performed on different regions of the middle leaves. Our results confirmed earlier reports that these pathogens have a higher affinity for the base of the lettuce leaf than the top. Differences of up to 2.12 log CFU/g were seen (E. coli O157:H7 86-24h11GFP). Intermediate attachment occurred in the central region.
The higher incidence of preferential bacterial attachment sites such as stomata and cell margins or grooves could not explain the differences observed in the association of the tested pathogens with different regions of iceberg lettuce leaves.
No comment from LGMA.
The N.Y Times reportsthe one place the one place the Salinas Valley’s bounty of antioxidants does not often appear is on the tables of the migrant workers who harvest it.
More than a third of the children in the Salinas City Elementary School District are homeless; overall diabetes rates are rising and projected to soar; and 85 percent of farmworkers in the valley are overweight or obese, partly because unhealthy food is less costly, said Marc B. Schenker, a professor at the University of California, Davis, who studies the health of farmworkers.
Hygiene indicators (total coliforms, Escherichia coli), and selected foodborne pathogens (Salmonella spp., Listeria monocytogenes, and Escherichia coli O157:H7) of water and leafy green vegetables were analyzed. Microbiological parameters of all irrigation water (except borehole) exceeded maximum limits set by the Department of Water Affairs for safe irrigation water. Microbial parameters for leafy greens ranged from 2.94 to 4.31 log CFU/g (aerobic plate counts) and 1 to 5.27 log MPN/100g (total coliforms and E. coli). Salmonella and E. coli O157:H7 were not detected in all samples tested but L. monocytogenes was present in irrigation water (commercial and small-scale farm, and homestead gardens).
