If I’m eating pre-washed lettuce I just open the bag and throw it on the plate. Because there’s not much I can do, safety-wise, to it once it’s in my home. If there’s pathogenic E. coli, Listeria or Salmonella there (or others) I’m stuck with it.
Cindy Tran of the Daily Mail writes that Sydney, Australia nutritionist Susie Burrell recently talked about food safety risks on a local morning show including a recommendation to rewash prewashed leafy greens.
She said people should always wash their store-bought salads, even if the packaging says ‘pre-washed’.
‘You must wash those ones out of the bags. It does say pre-washed but I would always wash it again because it has sat there for a long period, you don’t know what the turnover time is.’
I’m following recommendations from a bunch of my food safety friends who reviewed the literature on cut, bagged, washed, ready-to-eat leafy greens from a few years ago. In the abstract, they write:
The panel concluded that leafy green salad in sealed bags labeled “washed” or “ready-to-eat” that are produced in a facility inspected by a regulatory authority and operated under cGMPs, does not need additional washing at the time of use unless specifically directed on the label.
Leafy green food safety risks need to be addressed before they get to me, all I can do by washing it again is increase the chance I cross-contaminate the salad precursor in my home. My purchasing choice is based in trust that growers, packers and processors know what they are doing, and do it. But at best, they can only remove 90-99% of what is there with a wash.
My wife does a better Minnosotan accent, spending her yute in Albert Lea, eh?
He didn’t like the photo, right, made by the creative couple of Heather and Christian, who used to work in my lab, and opened the conversation with, “How could you print that?”
I said it was an accurate description of what had been publically known about the leafy greens folks since the E. coli O157 spinach outbreak of 2006 (I’m old, waiting for news on the birth of my third grandson).
I said great, make it public, so people can judge on their own.
Fresh Express has now been linked to 395 cases of Cyclospora through their lettuce served at McDonalds.
U.S. Rep. Rosa DeLauro, D-Conn., is pressing Food and Drug Administration Commissioner Scott Gottlieb for specifics about the investigation of the cyclosporaoutbreak linked to product sold by Fresh Express.
In an Aug. 3 letter her office released to the media, DeLauro said she wrote the letter “out of concern about the current outbreak of cyclosporiasis as well as the transparency and timeliness of your agency’s ongoing investigation.”
“Although once rare in the United States, parasitic outbreaks caused by cyclospora have become more common over the last several decades,” she said in the letter. “Many of these outbreaks have continually been found to be associated with imported fruits and vegetables.”
The recent outbreak is currently responsible for 395 infections — including 16 hospitalizations — across 15 states.
The parasite was first found when the FDA conducted testing on an unused package of Fresh Express salad mix, distributed to a McDonald’s restaurant, containing romaine lettuce and carrots.
The FDA states as of July 13, McDonald’s decided to stop selling the salads at restaurants impacted in Illinois, Iowa, Indiana, Wisconsin, Michigan. Ohio, Minnesota, Nebraska, South Dakota. Montana, North Dakota, Kentucky, West Virginia and Missouri.
In a July 20, statement, McDonald’s said the health and safety of their customers is their top priority.
“The health and safety of our customers and the people who work in McDonald’s restaurants is always our top priority. The additional states identified by the FDA and CDC are among the same states where a week ago we proactively decided to remove our lettuce blend in impacted restaurants and replace it through a different supplier. McDonald’s is committed to the highest standards of food safety and quality and we continue to cooperate and support regulatory and public health officials in their investigations. For those seeking additional information about Cyclospora, we encourage them to visit the CDC and FDA websites.”
Cyclospora sucks. My aunt, my mom’s sister, got it in Florida from basil, about a decade ago.
(Doesn’t she look amazing at 80, left.)
Cyclospora isn’t one of those things doctors routinely check for. Then you’re sick for about six weeks until some bright doc figures it out.
The U.S. Department of Agriculture’s Food Safety and Inspection Service (FSIS) issued an alert to the public on “beef, pork and poultry salad and wrap products potentially contaminated with Cyclospora that were distributed by Caito Foods LLC, of Indianapolis,” Indiana.
USDA also released a public health alert after Indianapolis-based food distributor Caito Foods “received notification from their lettuce supplier, Fresh Express, that the chopped romaine that is used to manufacture some of their salads and wraps was being recalled.”
“Fresh Express follows rigid food safety requirements and preventive controls throughout our supply chain that are carefully designed to mitigate against potential health risks. Working together with public health officials, we are hopeful a definitive source of the outbreak clusters will be identified soon.”
Still here, Mike. You can call me in Australia through Google voice 785-532-1925 and tell me what Fresh Express is doing, and why they are importing lettuce in the middle of North American summer.
Several outbreaks of foodborne illness traced to leafy greens and culinary herbs have been hypothesized to involve cross-contamination during washing and processing. This study aimed to assess the redistribution of Salmonella Typhimurium LT2 during pilot-scale production of baby spinach and cilantro and redistribution of Escherichia coli O157:H7 during pilot-scale production of romaine lettuce.
Four inoculated surrogate: uninoculated product weight ratios (10:100, 5:100, 1:100, and 0.5:100) and three inoculation levels (103, 101, and 10−1 CFU/g) were used for the three commodities. For each of three trials per condition, 5-kg batches containing uninoculated product and spot-inoculated surrogate products at each ratio and inoculation level were washed for 90 s in a 3.6-m-long flume tank through which 890 L of sanitizer-free, filtered tap water was circulated. After washing and removing the inoculated surrogate products, washed product (∼23, 225-g samples per trial) was analyzed for presence or absence of Salmonella Typhimurium or E. coli O157:H7 by using the GeneQuence Assay.
For baby spinach, cilantro, and romaine lettuce, no significant differences (P > 0.05) in the percentage of positive samples were observed at the same inoculation level and inoculated: uninoculated weight ratio. For each pathogen product evaluated (triplicate trials), inoculation level had a significant impact on the percentage of positive samples after processing, with the percentage of positive samples decreasing, as the initial surrogate inoculation level decreased.
The weight ratio of contaminated: noncontaminated product plays an important role: positive samples ranged from 0% to 11.6% ± 2.05% and from 68.1% ± 33.6% to 100% among the four ratios at inoculation of 10−1 and 101 CFU/g, respectively.
To our knowledge, this study is the first to assess the redistribution of low levels of pathogens from incoming product to leafy greens during processing and should provide important data for microbial risk assessments and other types of food safety analyses related to fresh-cut leafy greens.
Transfer and redistribution of Salmonella typhimurium LT2 and Escherichia coli O157:H7 during pilot-scale processing of baby spinach, cilantro, and romaine lettuce
Journal of food Protection vol.81 no. 6 June 2018
HALEY S. SMOLINSKI,1 SIYI WANG,1 LIN REN,1 YUHUAN CHEN,2 BARBARA KOWALCYK,3 ELLEN THOMAS,3 JANE VAN DOREN,2 and ELLIOT T. RYSER1*
Because it is consumed raw, anything that fresh fruit and vegetables come in contact with from the field to the home can really only increase risk. Washing and rinsing can remove at most 99% of what’s there. Microbiologically speaking, because there may be tens of thousands of cells on a leaf of Romaine, that’s not a whole lot. Often produce-related outbreaks are linked to poop getting into the food somewhere — wildlife on the farm; water used for irrigation or rinsing; soil and/or manure; or, the people who harvest, pack, handle and prepare it.
The problem with this outbreak is that the world of food safety sleuths have yet to figure it out. This one is particularly hard because the supply chain is a mess and investigators are trying to piece together what the farms and packing facilities looked like, food safety-wise, retroactively. Partners in figuring out outbreaks, the U.S. Centers for Disease Control and Prevention and the U.S. Food and Drug Administration have only been able to trace the problem to a specific geographic location – Romaine that was grown in the Yuma, AZ region.
Having a good sense of the supply chain for food, so outbreaks and incidents can be solved, is something that the industry has struggled with for decades. Even with the increased use of electronic records and the promise of blockchain, the data that gets recorded and shared relate to location and how food safety is managed from production to distribution to the grocery store still relies on people to input it.
Better traceability is often held up as a magic bullet but can’t really stop outbreaks from happening alone. Being able to trace a product is wholly reactive. While it is part of a good food safety culture even a good traceability program doesn’t wipe raw poop off of foods.
What keeps food safe is vigilance by the food industry, learning from past outbreaks and focusing on carrying out best practices daily. Lots of food companies talk about food safety. Implementing it daily is much harder. It takes a system throughout the entire company from the front-line staff all the way to the CEO that values food safety. Everyone needs to understand why food safety matters, what their role is and care about the folks who eat their products.
Where I grew up, there was a small tailgate farmers market Saturday mornings in the parking lot adjacent to the grocery store. I never really wondered whether the food sold there was safe. I didn’t think a whole lot about food safety and regulation until years later. I figured that if someone could sell it, they must know what they are doing, and I didn’t have to worry about it.
Food safety is all about trust, and I had lots of it.
A listing of 78 outbreaks linked to leafy greens since 1995 is posted here.
Maggie Menditto, the executive administrator of the McDowell Foundation for social justice, writes in the New York Times that before my illness, I was a healthy 22-year-old just out of college. But at some point, my doctors speculated, I must have eaten leafy greens contaminated by E. coli bacteria.
My mother had driven me to my local emergency room in the middle of the night after several days of unbearable abdominal cramps and a startling amount of blood coming out of new and terrifying places. The doctor on call thought it was probably just a bad case of colitis.
As the sun began to rise, I was asked if I’d like to go home and take Imodium or if I’d like to stay in the hospital. Given the severity of my pain, I was surprised that I was even given a choice. I allowed myself to be wheeled upstairs with a needle in my vein administering a steady stream of antibiotics, a common treatment for colitis.
But that weekend, I took a turn for the worse, throwing up every hour until there was nothing left in my system but sticky green bile. An infectious disease doctor was called in, my stool sample tested, and I was finally given a diagnosis of E. coli infection.
Doctors don’t know for sure how I became infected with E. coli — at the time, last October, the outbreak tied to romaine lettuce was still several months in the future — but we do have some clues. I’m a vegetarian, so we know it didn’t come from eating meat. Although none of my family members got sick, my father also tested positive for E. coli. The only food we remembered sharing was a batch of arugula from a local farmers’ market about five days before I became ill, making it the most likely culprit.
The antibiotics were immediately stopped, as they have been linked to an increased likelihood of developing dangerous complications from the bacterial infection. But by then the signs were already beginning to show. My platelet count was dropping at a dangerous rate, my kidney function had begun to falter. I had developed hemolytic uremic syndrome, a life-threatening complication of E. coli infection.
I was treated to the first ambulance ride of my life to transfer to Georgetown University Hospital, where I would remain hospitalized for the next 33 days.
In the critical care unit, I was strapped into several machines that would monitor my vitals. The next morning, a doctor came in and inserted a temporary access catheter into the right side of my neck. I was wheeled down to a lower level of the hospital for the first of my six plasmapheresis treatments, a particularly draining experience in which blood was removed, cleaned and then returned to my body via a large tube in my neck.
A team of hematologists, nephrologists, infectious disease specialists and a general physician visited every morning. They’d ask, “How are you feeling, Frances?”
Everyone knows me as Maggie, but in an annoying quirk of my hospitalization, my medical records and wristband all bear my legal name, Frances. “One name for each grandmother,” my mom reasoned when my parents decided to christen me Frances Margaret. An unintended consequence of their thoughtfulness is that I have spent much of my life correcting people who called me Frances. “It’s Maggie, short for Margaret, my middle name,” I said.
But in the hospital, it helped to have a second persona. Frances put on a brave face during the hours of treatment in sterilized facilities, while Maggie drew inward, refusing books and music or anything else that reminded me of who I was outside the hospital walls. From where I sat, pinned to machines by the needles in my veins, in a body I hardly recognized, and with a label on my wrist displaying a name that wasn’t mine, I couldn’t be sure that it was me this was really happening to. I listened patiently as doctors and nurses and technicians came into my room to offer Frances their well wishes, draw blood, or discuss what medications she should take or what procedures might make her body strong once more.
During my first week of hospitalization, the kidney doctors debated whether to begin the dialysis process, sticking to the typical “wait-and-see” approach. But by the end of the week there was no question. I had gained 30 pounds from all the excess fluid and could hardly stand up and walk on my own. I began my first of many three-hour-long dialysis treatments, where they siphoned off the liquid, doing the work of my kidneys that I had so long taken for granted.
I had mostly avoided social media since getting sick, but one day, I logged onto Facebook to see that across the country, people I knew and people I didn’t — a pair of girls I once babysat for, a football team in Rhode Island — were praying for Maggie, hoping Maggie pulled through. The more people that worried about me, the sicker I must be, I thought.
The dialysis continued for three weeks with tiny but measurable results. My platelet counts began to climb, and I started to pee again. But it wasn’t enough to impress the nephrologists, who decided to surgically place a catheter in my chest, to both drain and administer fluids.
Doctors began discussing a kidney transplant and temporary home-care dialysis training. I was sent home for a weekend to rest up before my first training for an eventual dialysis machine to be brought to my parents’ house, but we didn’t get that far. I went to bed after dinner and woke up in an ambulance racing back to the hospital I had just left. My blood pressure had begun a dangerous rise as my kidneys began to start working again, and I had the first of three seizures that night.
The next few days are mostly lost from memory, but some hazy images survive. Waking up in a tube to discover I was getting an M.R.I. A nurse delicately pulling glue from my hair from where the technicians had inserted sensors. My hospital bed being wheeled out of the operating room after the catheter was removed from inside my chest. The sharp lines of the white hallway walls, every corner offering a shadowy descent into someone else’s hospital story.
Through my half-closed lids, I see a rare pocket of sunlight at the end of the corridor. Briefly I feel the warmth of its gaze as we trek on through the seemingly endless maze of the hospital’s hallways and locked doors. The dryness in my mouth is the first clue that I’m back in my body, that my kidneys have begun to heal themselves at an admirable pace.
My mom finds me soon after, as I’m attempting to drink water from a clear plastic straw. She reaches out and holds it in place. The nurse comes in to tell us that it all went well, that Frances’s vitals look good, that we’ll be ready to transfer her back upstairs soon.
“She goes by Maggie,” my mom says.
“Oh, I’m sorry,” the nurse says, glancing down at her chart before stepping back into the hall, “Maggie.”
I turn to smile at my mom. It doesn’t matter what they call me anymore. She holds my hand as we’re guided back upstairs to my hospital room for the last time.
Sometimes now, in my apartment, on the train, while walking down a crowded street, I like to run my fingers over the fresh scars lining my collarbone. Now that the toxins have left my system, now that my body has built itself back up, I have only the scars to remind me that Frances was tested, that Maggie survived. That it really happened to me.
“All the doctors came in, and it was kind of like a big surprise like ‘It’s E. coli,'” Mia said.
The 16-year-old is a dancer who enjoys eating healthy. It’s not uncommon for her to grab a salad from the store, which is exactly what she did earlier this month. However, after eating it she became sick and was throwing up with abdominal pain.
“It was a scary process and I wouldn’t want to go through it again,” she said. “I know everyone else wouldn’t want to go through it.”
After four days in the hospital no one could figure out what exactly was wrong.
Just as Mia was heading home she learned her diagnosis. A relief for her mom Tina.
“Had we not gone back to the doctor and then gone to the emergency room, she could have gotten much sicker very quickly,” Tina Zlupko explained.
Now the teen is hoping to share an important message with others so no one else has to go through what she did.
“I’m definitely more aware and I want other people to be aware about it,” Mia said.
The CDC advisory now includes chopped and bagged romaine lettuce, as well as whole heads and hearts of romaine lettuce.
So far at least 64 people have been infected in 16 states. Pennsylvania is one place that has been hit the hardest with at least 12 people infected.
Officials think the outbreak is coming from Yuma, Arizona. They warn people not to eat any romaine lettuce unless you know where it’s from.
As of January 10, 2018, there were 42 cases of E. coli O157 illness reported in five eastern provinces. Individuals became sick in November and early December 2017. Seventeen individuals were hospitalized. One individual died.
The likely source of the outbreak in the United States appears to be leafy greens, but officials have not specifically identified a type of leafy greens eaten by people who became ill. Leafy greens typically have a short shelf life, and since the last illness started a month ago, it is likely that contaminated leafy greens linked to this outbreak are no longer available for sale. Canada identified romaine lettuce as the source of illnesses there, but the source of the romaine lettuce or where it became contaminated is unknown.
Whole genome sequencing (WGS) showed that the STEC O157:H7 strain from ill people in the United States is closely related genetically to the STEC O157:H7 strain from ill people in Canada. WGS data alone are not sufficient to prove a link; health officials rely on other sources of data, such as interviews from ill people, to support the WGS link. This investigation is ongoing. Because CDC has not identified a specific type of leafy greens linked to the U.S. infections, and because of the short shelf life of leafy greens, CDC is not recommending that U.S. residents avoid any particular food at this time.
In the United States, a total of 24 STEC O157:H7 infections have been reported. Among the 18 ill people for whom CDC has information, nine were hospitalized, including one person in California who died. Two people developed hemolytic uremic syndrome, a type of kidney failure.
The Public Health Agency of Canada identified romaine lettuce as the source of the outbreak in Canada. In the United States, the likely source of the outbreak appears to be leafy greens, but health officials have not identified a specific type of leafy greens that sick people ate in common.
State and local public health officials continue to interview sick people in the United States to determine what they ate in the week before their illness started. Of 13 people interviewed, all 13 reported eating leafy greens. Five (56%) of nine ill people specifically reported eating romaine lettuce. This percentage was not significantly higher than results from a survey of healthy people in which 46% reported eating romaine lettuce in the week before they were interviewed. Based on this information, U.S. health officials concluded that ill people in this outbreak were not more likely than healthy people to have eaten romaine lettuce. Ill people also reported eating different types and brands of romaine lettuce. Currently, no common supplier, distributor, or retailer of leafy greens has been identified as a possible source of the outbreak. CDC continues to work with regulatory partners in several states, at the U.S. Food and Drug Administration, and the Canadian Food Inspection Agency to identify the source.
Although the most recent illness started on December 12, there is a delay between when someone gets sick and when the illness is reported to CDC. For STEC O157:H7 infections, this period can be two to three weeks. Holidays can increase this delay. Because of these reporting delays, more time is needed before CDC can say the outbreak in the United Stated is over. This investigation is ongoing.
In the UK each year roughly 20,000 people are hospitalised with food poisoning and 500 people die. Symptoms are unpleasant and include vomiting, diarrhoea and a high temperature, according to the NHS. There are a number of causes, including chemicals, toxins and bacteria. While it’s almost always an accident, food poisoning tends to affect people after they’ve eaten particular foods. According to the Australian Institute of Food Safety, this is because certain foods are more at risk of bacterial growth than others. Poultry Raw and undercooked poultry can be contaminated with campylobacter bacteria and salmonella. According to the Australian Institute of Food Safety, the bacteria can survive up until cooking kills them – so make sure you cook it thoroughly and don’t contaminate surfaces with raw chicken.
Cook poultry to an internal temperature of 74C (165F) to ensure safety, forget the jargon “cook thoroughly,”doesn’t tell me anything.
Eggs Last week it was revealed that Dutch eggs contaminated with insecticide may have entered the UK. They can also sometimes be contaminated with salmonella. You can avoid being affected by cooking eggs thoroughly, and avoiding foods that purposely contain undercooked eggs, like mayonnaises and salad dressings, according to the Australian Institute of Food Safety.
Leafy greens Because they are often eaten raw with no cooking process, bacteria like E.coli can easily affect you. However, according to the Australian Institute of Food Safety, washing them can reduce risk of harmful bacteria as well as chemical pesticides.
Well this all depends if the salad is pre-washed and labelled accordingly, if so, washing lettuce at home will only increase the risk of cross-contamination. Reducing the food safety risk with leafy greens begins well before it arrives in your home.
Raw milk This is where milk is unpasteurised, meaning it has not been heated up to kill harmful bacteria. It leaves you at a higher risk than regular milk of consuming bacteria like E.coli, salmonella and listeria.
Raw milk has always left an impression on me ever since I was a food tech in Alberta. The health department submitted a sample of raw milk from a community in Alberta where a significant number of kids became ill. I was responsible in analyzing the milk to determine the etiologic agent and I remember vividly looking at this black, overgrown agar plate, completely taken over by Campylobacter jejuni, poor kids.
Cheese A bacteria commonly found in cheese is staphylococcus aureus. It’s heat resistant, so the best way of avoiding cheese becoming contaminated is to store it at or under 5 degrees.
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
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.
Mike Hornick of The Packer writes that health officials will begin routinely asking listeria outbreak victims if they consumed leafy greens, according to the Centers for Disease Control and Prevention.
It was the first reported listeria outbreak in the U.S. associated with leafy greens, and the eighth with fresh produce. All occurred since 2008, according to an Aug. 26 report by the CDC.
“It is unclear whether the appearance of these outbreaks might be attributed to improved outbreak detection, changes in consumer behavior, or changes in production and distribution,” the report says. “Fresh produce processors are advised to review food safety plans and consider incorporating measures to avoid the growth and persistence of listeria.”
In the Ohio centered outbreak, the older questionnaire failed to identify a common source for seven infections reported by Nov. 30.
Then in December and January, eight new or previously interviewed patients or their representatives took part in open-ended interviews or provided shopper card records.
That revealed the connection. All reported consuming leafy greens in the month before the onset of illness.
Among these, seven reported romaine and six reported spinach, higher than national food consumption estimates of 47% and 24%, respectively. Six patients recalled consuming packaged salad, according to the report.
Dole Fresh Vegetables denied responsibility in two foodborne illness lawsuits that followed the outbreak.