Growth of Listeria monocytogenes and Listeria innocua on fresh baby spinach leaves: Effect of storage temperature and natural microflora

Leafy greens such as spinach may be contaminated with Listeria monocytogenes during pre-harvest and postharvest handling. Recent recalls issued for Listeria-contaminated leafy greens are driving the need for technologies to minimize safety issues in fresh and fresh-cut produce.

listeria.spinachThis study assessed the effectiveness of washing treatments as a postharvest practice to minimize the growth of the pathogen and L. innocua on fresh baby spinach leaves under different storage temperatures and to evaluate the feasibility of using L. innocua as a surrogate when access to BL2 facilities is difficult. Each microorganism had a different (P < 0.05) response to the type of washing treatment at room temperature (∼22 °C) and the pathogen was harder to remove from the leaves than the surrogate was. Growth data for L. monocytogenes and L. innocua on fresh baby spinach leaves at 5–36 °C were modeled using the Baranyi and Ratkowsky (secondary) models which were validated by comparing the root mean square error (RMSEs) and biases between the growth data and model predictions. The secondary models showed good agreement between observed and predicted values.

These models can provide useful input to quantitative risk assessment tools to evaluate the growth of pathogens in baby spinach during several stages of processing and distribution such as washing and cold storage. Although the natural microflora on fresh baby spinach leaves affected the growth parameters for both bacteria, the effect was not significant. Thus, in the specific case of spinach leaves, the study shows that L. innocua may be a suitable surrogate in growth studies of L. monocytogenes.

Postharvest Biology and Technology, Volume 100, February 2015, Pages 41–51, DOI: 10.1016/j.postharvbio.2014.09.007

Basri Omac, Rosana G. Moreira, Alejandro Castillo, Elena Castell-Perez


Food Safety Talk 68: We Found It In Wild Pig Feces

Food Safety Talk, a bi-weekly podcast for food safety nerds, by food safety nerds. The podcast is hosted by Ben Chapman and barfblog contributor Don Schaffner, Extension Specialist in Food Science and Professor at Rutgers University. Every two weeks or so, Ben and Don get together virtually and talk for about an hour.  They talk about what’s on their minds or in the news regarding food safety, and popular culture. They strive to be relevant, funny and informative — sometimes they succeed. You can download the audio recordings right from the website, or subscribe using iTunes.keith-richards-pic-wireimage-184790458

In Episode 68, Don bravely participated without a microphone boom.  Ben feels good despite his messy office.

Ben mentions that he is currently obsessed with the Rolling Stones and likes the Shine a Light Film, Jumpin’ Jack Flash, (the song not so much the Whoopi Goldberg spy comedy film), and the song Salt of the Earth from the Stones album Beggars Banquet.  They then discuss movies every kid needs to see before they turn thirteen such as Indiana JonesGhostbustersE.T., and Diary of a Wimpy Kid and classic kids books including The Hardy BoysEncyclopedia BrownThree InvestigatorsKey to the Treasure, and A Wrinkle in Time.

The guys then discuss their recovery after IAFP, as a follow-up to FST 66. As president of IAFP Don was very busy at the conference with meetings, breakfasts, committee responsibilities, and other assorted duties.  He made the conference manageable by shirking his student poster responsibilities, not going to any talks, and skipping PDG meetings. He did however give a talk on based on a paper he has been working on with his CDC and EHS-Net (pronounced S-net) colleagues.

The guys then drift to other podcasts, especially Alton Brown’s series and in particular one he did with William Shatner.  If you like podcasts, food, Alton Brown, or William Shatner, this stupendous podcast is highly recommended for you.

Thirty-five minutes in they decide that they should talk about food safety and get to Outbreak Flashback about a 2008 Salmonella Saintpaul outbreak that affected over 1400 nationally (as per Michelle Danyluk‘s suggestion. Initial CDC epidemiology analysis indicated the illnesses were associated with eating tomato dishes and FDA issued a health advisory on tomatoes.  This NEJM article shows the case control studies that layout why the CDC initially thought the source was tomatoes. After tomatoes were removed from the market the illness continued and with additional data available the CDC later concluded that jalapeño and Serrano peppers were the likely source.  Epidemiologic analysis was confounded by the fact that many illnesses were from restaurants where peppers were in dishes that contained multiple ingredients.  Additionally the production and supply chain was very complex as is shown in the FDA’s traceback diagram. A key aspect of this outbreak is that it significantly harmed reputation and sales of the tomato industry, which estimates $400 million lost dollars as a result of the FDA’s erroneous health advisory. Talk turned to growers seeking indemnification or financial compensation for situations when the government agencies are incorrect about outbreaks.

  The guys then discuss a voluntary recall by Wawona Packing Co. on fresh peaches and stone fruit.  A receiving company in Australia detected the presence of Listeria monocytogenes.  This later led to a recall of baked goods in Wegman’s supermarket chain presumably because Wegman’s baking process is not validated. There are a surprisingly high number of comments posted to the Wegman’s article in Food Safety News which caused the guys to consider if the public health implications of this recall are more significant than first thought.  For Listeria monocytogenes (LM) there are not a lot of outbreaks but rather sporadic cases; CDC estimates in 2013 there were 0.26 LM illness cases per 100,000 people in the US (for every case reported there are 2 cases not diagnosed).  The guys then discuss food safety gaps common in fresh produce including poorly executed washing processes and traceability deficiencies.

 In after dark the guys discuss that Dean Richard Linton, Dean of the NCSU College of Ag, has selected the 2014 Dean’s ice cream which is dark chocolate, tart cherries, chocolate chunks and marshmallow swirl.

Asparagus soup? Three deaths traced to new Listeria outbreak in Denmark

Three people have died from listeria-infested asparagus soup at Odense University Hospital.

asparagus.soupThe deaths are a result of a new listeria outbreak and are not related to the one that has been traced to the deli meat rullepølse, which has claimed 16 lives.

“There are two different outbreaks and they are not connected. In the asparagus soup, it is a completely different strain of listeria than in the rullepølse outbreak.”

Three of the infections proved fatal, with the most recent death in April.

A recent check by the Danish Food and Veterinary Service (Fødevarestyrelsen) found traces of listeria in three soups at Odense University Hospital and Svendborg Hospital. Listeria was also found in meatballs served with the soups.

In all, 38 people were infected through the rullepølse outbreak, with 16 dying within 30 days of being infected. The last recorded death was on August 25.

Listeria still isn’t nice to pregnant women (and others)

This study describes trends in the incidence of pregnancy-related listeriosis in France between 1984 and 2011, and presents the major characteristics of 606 cases reported between 1999 and 2011 to the French Institute for Public Health Surveillance through the mandatory notification system.

amy.pregnant.listeriaThe incidence of pregnancy-related listeriosis decreased by a factor of 12 from 1984 to 2011. This reduction was a result of progressive implementation of specific Listeria monocytogenes control measures in food production. A lower incidence of pregnancy-related listeriosis was observed in regions with a lower prevalence of toxoplasmosis. Given that dietary recommendations in pregnancy target both toxoplasmosis and listeriosis prevention, we suppose that recommendations may have been delivered and followed more frequently in these regions.

Cases reported between 1999 and 2011 (n=606) were classified as maternal infections with ongoing pregnancy (n=89, 15%), fetal loss (n=166, 27%), or live-born neonatal listeriosis (n=351, 58%). The majority of live-born neonatal listeriosis cases (n=216, 64%) were preterm births (22–36 weeks of gestation), of whom 14% (n=30) were extremely preterm births (22–27 weeks of gestation). Eighty per cent of mothers reported having eaten high risk food during pregnancy. A better awareness of dietary recommendations in pregnant women is therefore necessary.

Eurosurveillance, Volume 19, Issue 38

D Girard, A Leclercq, E Laurent, M Lecuit, H de Valk, V Goulet


Listeriosis, caused by Listeria monocytogenes, is an important foodborne disease that can be difficult to control and commonly results in severe clinical outcomes. We aimed to provide the first estimates of global numbers of illnesses, deaths, and disability-adjusted life-years (DALYs) due to listeriosis, by synthesising information and knowledge through a systematic review.


We retrieved data on listeriosis through a systematic review of peer-reviewed and grey literature (published in 1990—2012). We excluded incidence data from before 1990 from the analysis. We reviewed national surveillance data where available. We did a multilevel meta-analysis to impute missing country-specific listeriosis incidence rates. We used a meta-regression to calculate the proportions of health states, and a Monte Carlo simulation to generate DALYs by WHO subregion.


We screened 11 722 references and identified 87 eligible studies containing listeriosis data for inclusion in the meta-analyses. We estimated that, in 2010, listeriosis resulted in 23 150 illnesses (95% credible interval 6061—91 247), 5463 deaths (1401—21 497), and 172 823 DALYs (44 079—676 465). The proportion of perinatal cases was 20·7% (SD 1·7).


Our quantification of the global burden of listeriosis will enable international prioritisation exercises. The number of DALYs due to listeriosis was lower than those due to congenital toxoplasmosis but accords with those due to echinococcosis. Urgent efforts are needed to fill the missing data in developing countries. We were unable to identify incidence data for the AFRO, EMRO, and SEARO WHO regions.


WHO Foodborne Diseases Epidemiology Reference Group and the Université catholique de Louvain.

The Lancet Infectious Diseases, doi:10.1016/S1473-3099(14)70870-9

Noordhout, Charline Maertens De, Brecht Devleesschauwer, Frederick J. Angulo, Geert Verbeke, Juanita Haagsma, Martyn Kirk, Arie Havelaar, and Niko Speybroeck

Sushi restaurant in Jerusalem closed due to Listeria risk

An immediate closing order was issued on Sunday by the Municipal Court for Local Affairs and the Health Ministry against Sushi Garden, a restaurant at 21 Rehov Yirmiyahu in Jerusalem’s Romema quarter. Ministry inspectors said the restaurant presented an immediate danger to public health if it remained open. As a result, municipal authorities asked for the urgent court order, which was issued on the spot.

Sushi-Platter-720x460Inspectors found that it was operating without a license and had very bad hygienic conditions. An epidemiological investigation by the ministry uncovered the case of a pregnant woman who miscarried after suffering from listeriosis. The ministry said there is a  possibility that the source of the bacterial infection was food made in the Sushi Garden restaurant.

Reports of Listeria more than double in Hong Kong

The annual number of reports of a deadly disease resulting from foodborne bacteria have more than doubled from 2011 to last year as people eat more pre-packaged food, doctors at the Centre for Food Safety said on Wednesday. 

listeria4A total of 26 cases of listeriosis, a serious bacterial infection that has a mortality rate of about 20 per cent, were reported last year and in 2012. In the previous three years, the annual average number of reported cases was 11.

The disease is caused by Listeria monocytogenes, a type of bacteria which thrives on pre-prepared food that is refrigerated for more than a week. 

Sixteen cases have already been reported in the first seven months of this year. The disease can lead to miscarriage, stillbirth, blood and brain infections among high-risk people such as pregnant women, newborns and elderly people.

Some of the cases reported this year had resulted in miscarriages, the centre said.

We’re in waste managment: Liechtenstein thieves steal 1.3 tonnes of Listeria cheese

Germany’s food inspection office is concerned bad cheese will be sold either directly or indirectly, posing a health risk to anyone who consumes it, ATS reported on Tuesday.

sopranos.don't.fuck.with.usThe problem is the “Alp Sücka” cheese was found to be contaminated with listeria monocytogenes, a bacterium that causes listeriosis, a potentially deadly infection.

Liechtenstein’s food office had banned the cheese but during a check discovered that 236 five-kilogram wheels of the dairy product had gone missing, ATS said.

They were probably stolen from open containers where they were stored temporarily before planned destruction, the news agency reported.

The country’s prosecutor has launched an investigation into the cheese’s disappearance.

Listeria concerns on the rise for pregnant women?

Listeria has always been a concern, but according to a NBC news affiliate, it’s new.

amy.pregnant.listeriaAnd people wonder why mainstream journalism is dying.

“While normally this is a bacteria our bodies can fight off, for expecting women, it becomes more difficult because of a lowered immune system. Additionally, there is concern that the bacteria could be passed on to the fetus.”


Seek and ye shall find; Listeria in smoked trout in Denmark

With 15 dead and 38 sick from a Listeria outbreak in Denmark, there’s probably more testing going on.

And they’re finding Listeria.

smoked.troutThe northern Jutland company Geia Food has recalled a batch of røget ørred (smoked trout) after Listeria was found in some samples, according to a release from the food authority, Fødevarestyrelsen.

The fish is sold at Rema 1000 stores under the Musholm brand with expiration dates 25 September 2014 and 29 September 2014.

Fødevarestyrelsen has advised customers to throw away the fish or return it to the shop where it was purchased.

Halibut, called hellefish in Danish, from Hjerting Laks should also be binned or returned to the Irma supermarket where it was purchased.

According to both Fødevarestyrelsen and Metroxpress, frozen fish from as far back as 1 June may be infected. Hjerting Laks has previously had problems with listeria infection.

However, Statens Serum Institute (SSI) said that it has not yet heard of anyone contracting listeria from infected fish.


15 now dead 38 sick in Denmark Listeria outbreak

A fifteenth person has died from the Listeria outbreak, the Danish State Serum Institute (SSI) confirmed on Monday.

rullepølserThe number of those affected has also risen to 38, SSI said.

The outbreak has been traced to the deli meat rullepølse produced by the company Jørn A. Rullepølser, which has been shut down.

A total of 30 products – including variations of rullepølse, salami and hot dogs – were recalled.

The Danish Veterinary and Food Administration (Fødevarestrylsen) also warned on Monday of a listeria risk in halibut sold by the company Hjerting Laks that was sold in Netto, Irma and Føtex stores.

Fødevarestrylsen was criticised for not acting quickly enough in responding to the listeria outbreak, with the food and agriculture minister, Dan Jørgensen, saying that “serious mistakes” took place.