Survival of Escherichia coli on strawberries grown under greenhouse conditions

One of the benefits of living in Brisbane is the four seasons of strawberries, unlike the three weeks in Canada.

sorenne.strawberry.13We eat endless amounts.

There has been the occasional outbreak, usually due to ruminant contamination with shiga-toxin producing E. coli.

Strawberries are soft fruit that are not recommended to have a post-harvest wash due to quality concerns. Escherichia coli O157:H7 has been linked to outbreaks with strawberries but little is known about the survival of E. coli during the growth cycle of strawberries.

The survival of E. coli on strawberry plants during growing under greenhouses conditions was evaluated. Soil, leaves, and strawberries (if present) were artificially contaminated with an E. coli surrogate either at the time of planting, first runner removal (4 wk), second runner removal (8 wk), or one week prior to harvest. At harvest E. coli was recovered from the leaves, soil, and strawberries regardless of the contamination time. Time of contamination influenced (P < 0.05) numbers of viable E. coli on the plant. The highest survival of E. coli (P < 0.0001) was detected in soil that was contaminated at planting (4.27 log10 CFU g soil−1), whereas, the survival of E. coli was maximal at later contamination times (8 wk and 1 wk prior to harvest) for the leaves (4.40 and 4.68 log10 CFU g leaves−1) and strawberries (3.37 and 3.53 log10 CFU strawberry−1). Cross contamination from leaves to fruit was observed during this study, with the presence of E. coli on strawberries which had not been present at the time of contamination.

These results indicate that good agricultural best practices to avoid contamination are necessary to minimize the risk of contamination of these popular fruit with enteric pathogens. Practices should include soil testing prior to harvest and avoiding contamination of the leaves.

Food Microbiology, Volume 46, April 2015, Pages 200–203

Angela Laury Shawa, Amanda Svobodaa, Beatrice Jiea, Gail Nonneckeb, Aubrey Mendoncaa


Does E. coli persist in strawberry fields (not forever)

Irrigation water quality is one of those nagging issues for on-farm food safety and fresh produce: it’s difficult to model how persistent E. coli is and just how much of a threat is present. Or as my farmer friends say, if I’m going to lose the crop, I’m going to irrigate.

beatles-strawberry-fields-foreverA two-year field experiment was conducted in order to evaluate the persistence of generic Escherichia coli in strawberry after irrigation with naturally E. coli-contaminated surface water. Sixteen experimental plots representing actual field conditions were set, including two methods of irrigation (overhead and subsurface drip) and two mulch types (straw and plastic). Two irrigations were performed each year with water having an E. coli content varying between 460 and 2242 CFU per 100 ml. Strawberries were harvested before irrigation and 1, 4 and 24 h following irrigation. E. coli counts could not be determined in any of the 256 strawberry samples. Enrichment procedure revealed more positive samples under straw mulch (6.4%) compared to plastic mulch (4.3%), but this difference was not statistically significant (P = 0.3991). Higher strawberry contamination was also observed in overhead irrigation treatments (8.6%) compared to drip irrigation (2.1%) (P = 0.0674). The risk to detect E. coli in overhead-irrigated strawberries was 4.5-fold higher than in strawberries under drip irrigation. Four hours following irrigation, the risk to detect E. coli in fruits was 4.0-fold lower than the risk observed 1 h after irrigation. Increasing the delay to 24 h led to a 7.4-fold lower risk. In actual conditions that may be encountered in strawberry productions, this study showed a limited persistence of E. coli in strawberries following irrigation.

Persistence of Escherichia coli following irrigation of strawberry grown under four production systems: Field experiment


Mylene Genereux, Michele Grenier, Caroline Cote

Food Control, Volume 47, January 2015, Pages 103–107, DOI: 10.1016/j.foodcont.2014.06.037

Nottinghamshire fruit growers hit back at health scare as crops are given all-clear

From the I’ve-been-doings-things-this-way-all-my-life files comes word that strawberry growers across Nottinghamshire, UK, say their product is “perfectly safe” in light of a report from  the European Food Safety Agency which described frozen strawberries, along with raspberries, as an “emerging public health risk” after being linked to cases of the potentially fatal norovirus in Europe.

strawberryIIn 2012, almost 11,000 people in Germany were struck down by Norovirus.

The Food Safety Agency report warned that fruits could be contaminated by dirty water used in irrigation or to dilute fertiliser, or a lack of hygiene in the packing and freezing processes.

However, there have not been any confirmed outbreaks in Britain.

Maybe theirs some confusion between frozen and fresh.

Suzannah Starkey, of Starkey’s Fruit in Southwell, said, “We don’t want the British people to fall out of love with strawberries – you can’t get better anywhere else. They are at their very best at the moment.

“All the Starkey family have eaten the strawberries all their lives, straight from the bush, and have never had a single problem.” Our strawberries are subject to very stringent hygiene standards. The pickers always wash their hands before picking and are subject to spot checks by health inspectors. The punnets are heat-sealed and rapidly chilled, and are maintained at that level until they are taken off the shelf by the customer.”

Responding to the European Food Safety Agency report, Laurence Olins, chairman of British Summer Fruits, the UK body dedicated to the promotion of British-grown soft and stone fruits, said: “The UK fresh fruit crop does not pose a public health risk.

“This report is based on out-of-date references relating to a very specific issue with frozen berries from developing countries, imported into other parts of Europe in 2012.”

11,200 sick; German norovirus outbreak linked to Chinese frozen strawberries declared over

Authorities in Germany have declared an outbreak of norovirus among schoolchildren, first noted in late September, officially over after an apparent failure by catering operators to prepare frozen strawberries properly prior to their consumption.

The strawberries in question had been imported from China and were reportedly supplied by a catering company – said to be a distribitor to foodservice giant Sodexo – in ten different locations across Germany.

The outbreak led to more than 11,000 people, most of them schoolchildren, falling ill as a result of acute gastroenteritis in Berlin, Brandenberg, Thuringia, Saxony and Saxony-Anhalt.

Sources in the fresh produce trade indicated that lessons learned from the recent E coli outbreak in northern Germany had helped minimise the impact on the industry as a whole, with communication said to have been more coordinated and timed to reduce the spread of rumour and conjecture.

Comforting words for the 11,200 kids and their families who were barfing.

China’s quality watchdog maintains no disease-causing viruses were found on Chinese frozen strawberries.

Berry, greenhouse growers work on food safety

The California Strawberry Commission is in the midst of its second food safety risk assessment.

The Packer reports the commission itself — not third-party auditors — is doing the assessment, following the harvest gradually from south to north. The work began in late 2011, and should be completed sometime this year.

Groups like Ontario greenhouse veggie growers require that all members must pass an annual third-party food safety audit.

Third-party audits alone can be a useful tool but not enough. Some individual greenhouse operations participate in additional auditing and traceability schemes, but not everyone; and any commodity is only as good as its worst grower.

The California strawberry types are focusing on field issues such as water, wildlife, compost and labor because there are the major potential sources of foodborne illness singled out by the U.S. Department of Agriculture and others.

Carolyn O’Donnell, communications director for the Watsonville-based commission, said, “We have a hand-harvested crop, so we’re dependent on making sure farm workers who are the last people to touch strawberries before consumers do are aware they have a real important step in the food safety process.”

The same group of commission representatives is doing the assessment in every region of the state.

On its website, the commission recently expanded its food safety section at

The commission is also working with berry growers in Oregon and Washington to support their efforts in food safety education.

Following a deadly E. coli outbreak in July 2011 that was the result of a deer incursion in an Oregon strawberry field, growers in the state decided to take preventive measures in preparation for the 2012 season.

Laura Barton, trade development manager with the Oregon Department of Agriculture said, “It doesn’t matter what size grower is involved. It only takes one berry to impact the entire industry. One of the challenges we identified when we started talking about this was how to find all of the smaller growers. It’s not like there is a list.”

Redux: On-farm food safety for strawberry growers

On June 12, 1996, Dr. Richard Schabas, chief medical officer of Ontario (that’s a province in Canada), issued a public health advisory on the presumed link between consumption of California strawberries and an outbreak of diarrheal illness among some 40 people in the Metro Toronto area. The announcement followed a similar statement from the Department of Health and Human Services in Houston, Texas, which was investigating a cluster of 18 cases of cyclospora illness among oil executives.

Turns out it was Guatemalan raspberries, and no one was happy.

The initial, and subsequent, links between cyclospora and strawberries or raspberries in 1996 was based on epidemiology, a statistical association between consumption of a particular food and the onset of disease. The Toronto outbreak was first identified because some 35 guests attending a May 11, 1996 wedding reception developed the same severe, intestinal illness, seven to 10 days after the wedding, and subsequently tested positive for cyclospora. Based on interviews with those stricken, health authorities in Toronto and Texas concluded that California strawberries were the most likely source. However, attempts to remember exactly what one ate two weeks earlier is an extremely difficult task; and larger foods, like strawberries, are recalled more frequently than smaller foods, like raspberries.

By July 18, 1996, the U.S. Centers for Disease Control declared that raspberries from Guatemala — which had been sprayed with pesticides mixed with water that could have been contaminated with sewage containing cyclospora — were the likely source of the cyclospora outbreak, which ultimately sickened about 1,000 people across North America. Guatemalan health authorities and producers vigorously refuted the charges. The California Strawberry Commission estimated it lost $15-20 million in reduced strawberry sales.

The California strawberry growers decided the best way to minimize the effects of an outbreak – real or alleged – was to make sure all their growers knew some food safety basics and there was some verification mechanism. The next time someone said, “I got sick and it was your strawberries,” the growers could at least say, “We don’t think it was us, and here’s everything we do to produce the safest product we can.”

That was essentially the prelude for FDA publishing its 1998 Guidance for Industry: Guide to Minimize Microbial Food Safety Hazards for Fresh Fruits and Vegetables. We had already started down the same path, and took those guidelines, as well as others, and created an on-farm food safety program for all 220 growers producing tomatoes and cucumbers under the Ontario Greenhouse Vegetable Growers banner. And set up a credible verification system.

In Aug. 2011, Oregon health officials confirmed that deer droppings caused an E. coli O157:H7 outbreak traced to strawberries that sickened 14 people and killed one. William Keene, senior epidemiologist with Oregon Public Health, said the outbreak strain turned up in samples from fields in three separate locations.

So, in the same way spinach, lettuce and tomato growers have reinvented their food safety pasts, commissions representing berry growers in Oregon, Washington and California have banded together to promote good food safety practices.

The efforts begin this spring with education and training of growers and farm workers on proper handling of fresh fruit, according to a news release.

The best producers or manufacturers can do is diligently manage and mitigate risks and be able to prove such diligence in the court of public opinion; and they’ll do it before the next outbreak.

One dead, 10 sick from E. coli O157:H7 traced to Oregon strawberry farm

Oregon Public Health officials have identified fresh strawberries from a Newberg, Oregon, farm as the source of a cluster of Escherichia coli O157:H7 infections that sickened at least 10 people last month, including one person who died.

The strawberries were produced last month by Jaquith Strawberry Farm located at 23135 SW Jaquith Road in Newberg. Jaquith finished its strawberry season in late July, and its strawberries are no longer on the market. Jaquith sold its strawberries to buyers who then resold them at roadside stands and farmers’ markets.

Health officials are urging consumers who may have purchased strawberries grown on this farm to throw them out.

Strawberries that have been frozen or made into uncooked jam are of particular concern. Cooking kills E. coli O157:H7 bacteria.

"If you have any strawberries from this producer – frozen, in uncooked jam or any uncooked form – throw them out," says Paul Cieslak, M.D., from Oregon Public Health Division. He says people who have eaten the strawberries, but remain well need take no action. The incubation period for E. coli O157:H7 is typically two to seven days.

Ten people have confirmed an E. coli O157:H7 infection caused by a single strain. These individuals include residents of Washington, Clatsop, and Multnomah counties. Six other people in northwest Oregon also have recently developed an E. coli O157:H7 infection and appear to be part of this outbreak.

Of the confirmed cases, four have been hospitalized, and one elderly woman in Washington County died from kidney failure associated with E. coli O157:H7 infection. There were 12 females and four males among the cases, and their ages ranged from 4 to 85. They fell ill between July 10 and July 29.

Sabotage continues on Australian crops; biosecurity measures prevented latest attack

A saboteur who tried to poison a large strawberry crop in Queensland, Australia, has been foiled by tight security measures introduced after a similar attack in 2009.

Gowinta Farms at Beerwah, on the Sunshine Coast, would have been facing multi-million dollar losses if staff had not discovered poison in the farm’s water stores.

Spokesman James Ashby said up to 170 acres of strawberries would have been lost and the incident, detected on Tuesday, was a lesson for all farmers about the importance of good security.

After the 2009 attack, which destroyed a greenhouse crop of tomatoes and cucumbers, the farm imposed a system to drain water tanks at the end of each day and regularly test water quality.

As a result, the presence of the poison was obvious to staff on Tuesday morning, Mr Ashby said.

Meanwhile, police are still trying to find those responsible for a crop sabotage incident at Bowen in north Queensland in June last year.

In that incident, Bowen Supa Seedlings lost more than seven million fruit and vegetable seedlings, destined to become crops for dozens of local growers, when its irrigation system was contaminated with herbicide.

A neighbouring property that shared the irrigation system lost more than 16,000 mature tomato plants.