Biotic and abiotic variables affecting internalization and fate of Escherichia coli O157:H7 isolates in leafy green roots

Posted on May 24, 2014 by Douglas Powell

In the on-going discussion of whether dangerous pathogens can be internalized in leafy greens, Erickson, et al. write:

Preharvest internalization of Escherichia coli O157:H7 into the roots of leafy greens is a food safety risk because the pathogen may be systemically transported to edible portions of the plant. In this study, both abiotic (degree of soil moisture) and biotic (E. coli O157:H7 exposure, presence of Shiga toxin genes, and type of leafy green) factors were examined to determine their potential effects on pathogen internalization into roots of leafy greens.

Using field soil that should have an active indigenous microbial community, internalized populations in lettuce roots were 0.8 to 1.6 log CFU/g after exposure to soil containing E. coli O157:H7 at 5.6 to 6.1 log CFU/g. Internalization of E. coli O157:H7 into leafy green plant roots was higher when E. coli O157:H7 populations in soil were increased to 7 or 8 log CFU/g or when the soil was saturated with water. No differences were noted in the extent to which internalization of E. coli O157:H7 occurred in spinach, lettuce, or parsley roots; however, in saturated soil, maximum levels in parsley occurred later than did those in spinach or lettuce. Translocation of E. coli O157:H7 from roots to leaves was rare; therefore, decreases observed in root populations over time were likely the result of inactivation within the plant tissue.

Shiga toxin–negative (nontoxigenic) E. coli O157:H7 isolates were more stable than were virulent isolates in soil, but the degree of internalization of E. coli O157:H7 into roots did not differ between isolate type. Therefore, these nontoxigenic isolates could be used as surrogates for virulent isolates in field trials involving internalization.

Journal of Food Protection, Number 6, June 2014, pp. 872-1042, pp. 872-879(8)

Erickson, Marilyn C., Webb, Cathy C., Davey, Lindsey E., Payton, Alison S., Flitcroft, Ian D., Doyle, Michael P.

http://www.ingentaconnect.com/content/iafp/jfp/2014/00000077/00000006/art00001

That’s a lot of poop: nearly 179 million cases of acute diarrhea occur each year in US

Posted on April 23, 2014 by Douglas Powell

Washing produce is never enough, but that’s what a researcher says in a review of causes of foodborne illness. A better suggestion would be rigorous on-farm food safety programs.

In the United States, approximately 179 million cases of acute diarrhea occur each year, and most of those cases are entirely preventable, a researcher from The University of Texas Health Science Center at Houston (UTHealth) concluded in a New England Journal of Medicine review article.

Herbert L. DuPont, M.D., director of the Center for Infectious Diseases at the UTHealth School of Public Health, examined current causes, prevention strategies and treatment for acute diarrhea in healthy adults. He says the main causes of diarrheal infections include norovirus outbreaks and foodborne pathogens, with most coming from contaminated leafy green vegetables.

Produce is the most common source of diarrhea due to foodborne intestinal illness. Most consumers are not aware that 98 percent of spinach and lettuce bought from grocery stores is not inspected and much of it comes from developing countries. One study showed that of the 2 percent that is inspected, 40 percent failed inspection and could be contaminated by diarrhea-producing E. coli or Salmonella.

“Consumers need to give their leafy greens a bath and a shower in order to make sure they are safe to eat,” says DuPont, instructing that leafy greens must be soaked in a bowl of water or the sink and then rinsed thoroughly by running water through a colander before consumption in order to avoid contaminants.

CFIA plays the 99 per cent numbers game

Posted on April 13, 2014 by Douglas Powell

CFIA is getting into the 99 per cent game, usually reserved for hucksters on TV.

99.9 per cent sounds good, but that’s only a 3-log reduction. For food safety purposes, log-5 (99.999 per cent) to log-7 (99.99999 per cent) reductions in dangerous pathogens are often strived for.

Last week, the Canadian Food Inspection Agency announced that 99.8 per cent of whole cantaloupe samples tested negative for the presence of Salmonella (they didn’t test for Listeria, but should have).

Playing the 99 per cent game is also terrible risk communication: it doesn’t matter how small the percentage of positive samples were if you were one of the 23 people that dies from Listeria in Maple Leaf cold-cuts in 2008.

Data and sampling are a necessary evil and I’m glad CFIA is making the results public. But testing is limited and fraught with caveats. It’s expensive, and industry has lots of data, so why not make it public, in the context of an overall approach to food safety for a specific food.

CFIA reports a total of 499 whole cantaloupe samples were collected and tested for Salmonella bacteria, which can cause a serious illness with long-lasting effects. One sample was found to be unsatisfactory due to the presence of Salmonella.

A week later, CFIA said more than 99.9 per cent of leafy green vegetable samples had no detectable levels of bacterial pathogens and were safe to consume.

As part of a five-year microbiological plan that began in 2008/2009, the CFIA analyzed a total of 4,250 domestic and imported, whole and fresh-cut fresh leafy vegetable samples available in the Canadian market for Salmonella, E. coli O157:H7, E. coli O157:NM and generic E. coli. The fresh-cut samples were also tested for Listeria monocytogenes.

The 2009/2010 study deemed 12 samples to be “unsatisfactory” due to the presence of Salmonella, Listeria monocytogenes, and/or high levels of generic E. coli. None of the samples were found to be positive for E. coli O157:H7 or E. coli O157:NM.

Raw kale tale

Posted on January 9, 2014 by Ben Chapman

Ashley Chaifetz, a PhD student studying public policy at UNC-Chapel Hill writes,

Kale has become the food that apparently does everything: cancer protection, lower cholesterol, provides antioxidant vitamins A, C, and K and minerals iron and potassium, and in the improvement of eye health. Repeatedly called a “superfood” (a quick Google search will reveal over a million hits), kale is often consumed cooked, much like collard, mustard, and turnip greens.

Yet, I’ve been regularly seeing it served raw—in restaurant dishes, recipes in cooking magazines, in friends’ homes, and even in bagged salads at the grocery store. While it is delicious, I think a lot about how it was grown, processed, and packaged. Microbial food safety might not be number one for kale producers as they might reason that consumers and restaurants traditionally cook the greens and reducing pathogen risk in the process. The control point, historically was in the kitchen.

A couple of years ago, I’d think that raw kale was an anomaly, but given it’s popularity (see: 50 Shades of Kale cookbook, the fact that kale has had a 400% increase in menu appearances over the last 4 years, and even celebrities love it), it seems poised to stick around.

Now that there’s been such a shift to raw consumption, I trust that the industry has addressed the production, harvesting and packing related risks. As a shopper and eater, trust is about all I have since no one is talking about whether growers have taken the appropriate precautions so that it won’t make me sick.

It’s not just bacteria and viruses; parasites in leafy greens

Posted on February 17, 2013 by Douglas Powell

On July 7, 1997, a company physician reported to the Alexandria Department of Health (ADOH) that most of the employees who attended a corporate luncheon on June 26 at the company’s branch in Fairfax, Virginia, had developed gastrointestinal illness. On July 11, the health department was notified that a stool specimen from one of the employees who attended the luncheon was positive for Cyclospora oocysts. Many others tested positive. It was subsequently revealed in a July 19, 1997, Washington Post story citing local health department officials that basil and pesto from four Sutton Place Gourmet stores around Washington D.C. was the source of cyclospora for 126 people who attended at least 19 separate events where Sutton Place basil products were served, from small dinner parties and baby showers to corporate gatherings. Of the 126, 30 members of the National Symphony Orchestra became sick after they ate box lunches provided by Sutton Place at Wolf Trap Farm Park.

In May 2001, 17 people in British Columbia were sickened with cyclospora associated with basil from Thailand. In 2005, 300 people in Florida were sickened with cyclospora from fresh basil.

My aunt was part of that outbreak.

Parasites. They’re everywhere.

Canadian researchers report in the Journal of Food Protection a “relatively high prevalence” of Cyclospora, Cryptosporidium and Giardia in ready-to-eat packaged leafy greens; most of the products were grown in the U.S.

Abstract below.

Detection of Cyclospora, Cryptosporidium, and Giardia in ready-to-eat packaged leafy greens in Ontario, Canada

Journal of Food Protection®, Number 2, February 2013, pp. 192-369 , pp. 307-313(7)

Dixon, Brent; Parrington, Lorna; Cook, Angela; Pollari, Frank; Farber, Jeffrey

http://www.ingentaconnect.com/content/iafp/jfp/2013/00000076/00000002/art00016

Numerous foodborne outbreaks of diarrheal illness associated with the consumption of produce contaminated with protozoan parasites have been reported in North America in recent years. The present study reports on the presence of Cyclospora, Cryptosporidium, and Giardia in precut salads and leafy greens purchased at retail in Ontario, Canada. A total of 544 retail samples were collected between April 2009 and March 2010 and included a variety of salad blends and individual leafy greens. Most of these products were grown in the United States, with some from Canada and Mexico. Parasites were eluted and concentrated before detection by PCR and immunofluorescence microscopy. DNA sequences were aligned with reference sequences in GenBank. Cyclospora spp. were identified by PCR-restriction fragment length polymorphism in nine (1.7 % ) samples and by DNA sequence analysis. Cryptosporidium spp. were identified in 32 (5.9%) samples; 29 were sequenced and aligned with the zoonotic species Cryptosporidium parvum. Giardia duodenalis was identified in 10 (1.8%) samples, and of the 9 samples successfully sequenced, 7 aligned with G. duodenalis assemblage B and 2 with assemblage A, both of which are also zoonotic. The presence of Cryptosporidium oocysts and Giardia cysts was confirmed in some of the PCR-positive samples using microscopy, while Cyclospora -like oocysts were observed in most of the Cyclospora PCR-positive samples. The relatively high prevalence of these parasites in packaged salads and leafy greens establishes a baseline for further studies and suggests a need for additional research with respect to the possible sources of contamination of these foods, the determination of parasite viability and virulence, and means to reduce foodborne transmission to humans.

E. coli lasts longer in Salinas soil, study

Posted on November 15, 2012 by Douglas Powell

New research finds the pathogen E. coli O157:H7 lives about 30 days in soils from California’s Salinas Valley — 10 days more than in the state’s Imperial Valley or Yuma, Ariz.

Lower salinity in Salinas irrigation water is the main cause of the difference, said Mark Ibekwe, a microbiologist with the U.S. Department of Agriculture’s Agricultural Research Service in Riverside, Calif.

Mike Hornick of The Packer reports Ibekwe and three colleagues published their findings, “Persistence of Escherichia coli O157:H7 in Major Leafy Green Producing Soils,” in the journal Environmental Science & Technology in October.

The results were based on laboratory-tested soil samples. Field studies of E. coli are typically limited to nonpathogenic varieties.

Increasing salinity in Salinas water would not be realistic or beneficial for leafy greens growers there, Ibekwe said. Nevertheless, the research underscores the importance of keeping new pathogens from entering the fields.

“You don’t want to introduce another variable into the farming environment that will ultimately cause adverse effects on the crops and result in lower yield,” Ibekwe said. “Because of how salinity will react with other factors there, we are not suggesting that.

“What we’re saying is that because we know there’s a longer survival in the Salinas area, we should be very, very careful in introducing pathogens from manure, poorly composted materials or any source at all into the farming environment,” he said.

Cottage food discussion in Wyoming includes leafy greens; AFDO guidance document available

Posted on May 25, 2012 by Ben Chapman

Folks who want to make food in their home or garage and sell it are part of a growing business segment. By many accounts, the cottage food industry is growing in North America. The county extension agents I support are fielding an increased number of questions of how to break into the food industry in the past year. The situation in other states is apparently similar.

Twenty U.S. states allow certain foods to be processed in the home and sold for consumption – but it’s a patchwork of regulatory approaches. In some states, the entire process is deregulated for certain exempt products. These products usually are limited to direct-selling (at a farmers’ market or roadside stand) of baked goods, jams and jellies.

Last year Colorado jumped into cottage food rules including a requirement for small business folks to take a mandatory food handling course for foods deemed to be low risk (jellies, breads, etc).

In 2010 Michigan also adopted a new law allowing for home-based food production. In the absence of inspection, the law requires each item to have a label saying it was produced in an uninspected home kitchen, listing the food’s ingredients and any known allergens, and includes the producer’s name and address.

The cottage foods discussion has also popped up in Wyoming with a turn towards leafy greens and cut fruit processing, similar to discussions in North Carolina in April 2012.

From the Star-Tribune:

“People in Wyoming are concerned with food safety,” state Rep. Sue Wallis, R-Recluse said. “Many want to buy locally.”The problem is, according to Wyoming Department of Agriculture spokesman Derek Grant, unregulated processing of locally produced products, such as chopped lettuce or cantaloupe, increases the chances of contamination.One proposed rule allows farmers to sell leafy greens at a farmers market, for example, as long as they are not in a bag. If the greens are cut and placed in a bag, they are considered cut leafy greens and producers must meet sanitation requirements and obtain a license to sell them.Wallis said farmers in Jackson Hole have been selling bagged greens to local restaurants at the restaurants’ request.If the rule change is adopted, farmers will have to invest in a certified kitchen, with equipment to meet department requirements for cleaning the greens.

While it might not be a current followed regulation, it’s best practice to manage cut leafy greens (things like shredded lettuce, etc) like a high risk food, processed in a clean environment, and the end product kept at refrigeration temperatures. Following over 20 multi-state outbreaks between 1998 and 2008, ‘cut leafy greens’ was added to the definition of potentially hazardous food requiring time-temperature control for safety (TCS) in the U.S. FDA Model Food code.

Storage and transport time and temperature are contributing factors for pathogen growth in cut leafy greens; water and nutrient availability, along with a suitable pH create an environment to support the growth of lots of foodborne bacteria. This is similar for other cut/minimally processed fruits and vegetables like melons, tomatoes and sprouts.

In response to cottage food excitement, our friends at the Association of Food and Drug Officials (AFDO) have released a guidance document (unfortunately it’s not free) defining the types of foods that should fall under cottage food exemptions, and those, like cut fruits and vegetables, which should require some sort of commercial facility.

The scope of these guidelines is comparable to those accepted practices currently recognized in several states and represents a consensus opinion of AFDO members. AFDO believes that adopting and implementing these guidelines, where there is little or no oversight of such activities, can eliminate a void in the national goal of a seamless food safety and security system

The guidance document can be found at http://www.afdo.org/publications.

Having a mandatory food handler course for exempt processors, like Colorado does, based on the AFDO guidance document, might help avoid the sometimes tragic outbreaks.

No need to rewash pre-washed leafy greens; Academy of Nutrition and Dietetics misses the evidence-based message again

Posted on May 22, 2012 by Ben Chapman

My friends at the Academy of Nutrition and Dietetics are at it again. Last week they recycled a press release on the dangers of reusable bags that was full of holes, This week Sarah Kriegar of The Academy decided to remind folks that washing pre-washed leafy greens is a good idea.

“Fruits and vegetables are an important part of a healthy eating plan, and should fill half of your plate, but just like any food product, extra precautions should be taken to reduce the risk of food poisoning,” said Sarah Krieger, a registered dietitian and academy spokeswoman, in a statement.
She said (among other things -ben):

– Buy loose produce rather than pre-packaged, but if you do buy packaged lettuce or carrots or other items, wash them even if they say “ready to eat.”

I’d like to see what data The Academy has that shows this recommendation would result in risk-reduction.

Washing pre-washed leafy greens in the home isn’t going to accomplish further risk-reduction than what was applied at processing; tight attachment or internalization of the target pathogens are likely for whatever is left when it gets to someones kitchen.

A review paper published in Food Protection Trends in 2007 contained guidelines developed by a national panel of food safety folks and concluded:

"… 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.”
The panel also advised that additional washing of ready-to-eat green salads is not likely to enhance safety.

“The risk of cross contamination from food handlers and food contact surfaces used during washing may outweigh any safety benefit that further washing may confer."

A table of leafy green-related outbreak is available at http://bites.ksu.edu/leafy-greens-related-outbreaks. I’m not sure there’s any data out there that shows washing would have been a protective step for any of the outbreaks.

The merits of washing produce at home are debatable – many papers show somewhere around a 1-log reduction of pathogens from washing produce with no difference whether the fruit or vegetable was washed with water or some sort of sanitizer. A ten-fold reduction is okay if there isn’t much pre-home contamination, but washing as a kill step sucks and is really more about increasing quality(removing grit). Effective risk reduction actions for fresh produce are more likely found in production, processing and food service preparation (where contamination often occurs) – not in home kitchens.

Should pre-washed, bagged leafy greens be washed again at home? NPR says yes, many food safety types say no

Posted on April 19, 2012 by Douglas Powell

Should bagged, pre-washed salad greens be washed again in the home kitchen?

Many food safety types say no.

During the idle but oh-so-smoothing brand of chat-chit practiced by National Public Radio that preceded a story about E. coli and Salmonella in leafy greens from Salinas, Calif., one reporter said, “I wash it every time but I don’t know if it actually helps.”

Reporter Dan Charles responded, “It says prewashed but washing might help.”

So might a lot of others things not fit for this family publication.

A review paper published in Food Protection Trends in 2007 contained guidelines developed by a panel of food safety types and concluded:

The panel also advised that additional washing of ready-to-eat green salads is not likely to enhance safety.

“The risk of cross contamination from food handlers and food contact surfaces used during washing may outweigh any safety benefit that further washing may confer."

When washing at home, "there’s a risk that is the sink where you just washed your chicken," said Donald Schaffner, Rutgers University professor of food science, in a 2011 interview.

Today’s NPR soothfest revisited what growers in California are doing to enhanced food safety and the 2006 E. coli O157:H7 outbreak in spinach that killed 3 and sickened at least 200.

Will Daniels, senior vice president for operations and organic integrity at Earthbound Farm, based in San Juan Bautista, told NPR, "I was at the center of the investigation and really took it very hard. It was just a real tough time to go through, and something that I don’t ever want to go through again."

Investigators found E. coli bacteria that matched the microbes that were making people sick on a ranch that was one of Earthbound’s suppliers. But those bacteria were in animal feces a mile from the spinach field, Daniels says, "with no clear indication of what caused the contamination from a mile away to get into the spinach field itself."

"Unfortunately, it looks like every animal is suspect," says Bob Martin, general manager of Rio Farms, in King City, Calif.

Even birds. "Birds are a big issue! They carry human pathogens, and we can’t put diapers on them. We can’t dome our fields; there’s nothing we can do, short of trying to scare them away.”

Lettuce fields now have to be separated from cattle pastures, and throughout the valley, next to lettuce fields, you see white plastic pipes. Inside those pipes are mouse traps.

And the birds? Vegetable buyers won’t take anything from the area directly under power lines.

"When it comes to food safety, if it’s grown outdoors, forget it, there’s no such thing as zero tolerance," says Bob Martin. "And everybody knows that, except for some food safety personnel of the big food buyers."

Daniels of Earthbound Farms was further quoted as saying, "It is a true test-and-hold program, so we have to wait to get the negative results before we put it on a truck. Any positives go to the landfill.”

There still are positives. Not very often, but every five weeks or so, one of these tests catches a sample that’s contaminated with disease-causing E. coli or Salmonella.

A table of leafy green related outbreak is available at http://bites.ksu.edu/leafy-greens-related-outbreaks.

Leafy greens cone of silence; some hometowners don’t believe it; need to provide stool sample to health unit

Posted on August 3, 2010 by Douglas Powell

The Sacramento Bee in California reports that the latest E. coli O157:H7 in lettuce recall prompted Bee readers to express disbelief that state public health officials had not received any reports that anyone had gotten sick from potentially tainted bags of pre-packaged salad mix.

One Sacramento woman said she and her son were hospitalized after eating the salad, which was the subject of a recall. Several other callers also said that, without a doubt, they had eaten from a bag of bad product.

But none of those who contacted The Bee said they had taken the time to call local health officials (those are the tools, right and left, to provide a stool sample; thanks, Ben).

If consumers suspect that tainted food has made them ill, they should contact their doctor, said state Public Health Department spokesman Ralph Montaño. A doctor can help determine whether tainted food was potentially the cause and if necessary contact the county public health department.

barfblog

safe food from farm to fork

Tag Archives: leafy greens