Distributions of Salmonella subtypes differ between two U.S. produce-growing regions

Salmonella accounts for approximately 50% of produce-associated outbreaks in the United States, several of which have been traced back to contamination in the produce production environment. To quantify Salmonella diversity and aid in identification of Salmonella contamination sources, we characterized Salmonella isolates from two geographically diverse produce-growing regions in the United States.

supermarket_produce Initially, we characterized the Salmonella serotype and subtype diversity associated with 1,677 samples collected from 33 produce farms in New York State (NYS). Among these 1,677 samples, 74 were Salmonella positive, yielding 80 unique isolates (from 147 total isolates), which represented 14 serovars and 23 different pulsed-field gel electrophoresis (PFGE) types. To explore regional Salmonella diversity associated with production environments, we collected a smaller set of samples (n = 65) from South Florida (SFL) production environments and compared the Salmonella diversity associated with these samples with the diversity found among NYS production environments. Among these 65 samples, 23 were Salmonella positive, yielding 32 unique isolates (from 81 total isolates), which represented 11 serovars and 17 different PFGE types.

The most common serovars isolated in NYS were Salmonella enterica serovars Newport, Cerro, and Thompson, while common serovars isolated in SFL were Salmonella serovars Saphra and Newport and S. enterica subsp. diarizonae serovar 50:r:z. High PFGE type diversity (Simpson’s diversity index, 0.90 ± 0.02) was observed among Salmonella isolates across both regions; only three PFGE types were shared between the two regions. The probability of three or fewer shared PFGE types was <0.000001; therefore, Salmonella isolates were considerably different between the two sampled regions. These findings suggest the potential for PFGE-based source tracking of Salmonella in production environments.

Appl. Environ. Microbiol. July 2014 vol. 80 no. 13 3982-3991 doi: 10.1128/AEM.00348-14

Laura K. Strawna, Michelle D. Danylukb, Randy W. Woroboa and Martin Wiedmann

http://aem.asm.org/content/80/13/3982.abstract.html?etoc

The limitations of washing fresh produce at home

A couple of weeks ago my friend Matt Shipman, who runs The Abstract, asked me to answer a question about the best way to wash produce in the home.

I’ve received different iterations of this question up from extension agents, media and at Food Safety Talk with Don Schaffner. I’ve sort of settled on this: use water, vigorously running out of the tap, but don’t expect washing to make your produce risk-free. HE_washing-pepper_s4x3_lead

I used to say that washing in the home did nothing for food safety but Don, the smart math dude I hangout with electronically, reminded me that saying it does nothing is incorrect – it does something.

Just not as much as folks may expect.

Matt captured the discussion for a blog post, below.

Here’s the question we got: “What is the most effective means of cleaning fresh produce at home to remove micro-organisms that could make you sick?”

“Vigorously rinsing the produce under running water is the most effective way of removing the microbes that cause foodborne illnesses – you don’t need soap or any special cleaning products,” says Ben Chapman, a food safety researcher at NC State. “But while washing your produce may remove some pathogens, it doesn’t eliminate risk altogether.”

“At best you get a two log reduction – that’s a 99 percent reduction in microbes,” Chapman says. “That seems good, but it’s not great. While washing can help reduce pathogen contamination, it shouldn’t be relied on as the only control measure.”

By comparison, cooking food results in a six log reduction in viable microbes. That means the population of viable microbes gets cut by 99.9999 percent(!).

The difference between 99 percent and 99.9999 percent is important because some fruits and vegetables can be contaminated with thousands of microbes. And we know that, on average, most microbial food-borne illnesses are caused by foods that are contaminated by only 20-30 organisms (the mean infectious dose for some of the pathogens of concern -ben).

So washing off 99 percent of the microbes doesn’t help much if a food was carrying thousands of microbes to start with. 

Buy from producers who know what the risks are and are employing strategies to reduce them. Ask lots of questions.

Some good references on how I’ve arrived at my answer are here: Bassett and McClure 2008Parish et al., 2003; Parnell et al., 2005; Verrill et al., 2012. There are other good ones out there too including this fact sheet from Christine Bruhn and others.

Aerosol sanitization to control pathogens on produce

An economical aerosol sanitization system was developed based on sensor technology for minimizing sanitizer usage, while maintaining bactericidal efficacy.

Aerosol intensity in a system chamber was controlled by a position-sensitive device and its infrared value range. The effectiveness of the infrared sensor–based aerosolization (ISA) system to inactivate Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on spinach leaf surfaces was compared with conventional aerosolization (full-time aerosol treated), and the amount of sanitizer consumed was determined after operation.

berries.may.14Three pathogens artificially inoculated onto spinach leaf surfaces were treated with aerosolized peracetic acid (400 ppm) for 15, 30, 45, and 60 min at room temperature (22 ± 2°C). Using the ISA system, inactivation levels of the three pathogens were equal or better than treatment with conventional full-time aerosolization. However, the amount of sanitizer consumed was reduced by ca. 40% using the ISA system. The results of this study suggest that an aerosol sanitization system combined with infrared sensor technology could be used for transportation and storage of fresh produce efficiently and economically as a practical commercial intervention.

 Infrared sensor–based aerosol sanitization system for controlling Escherichia coli O157:H7, Salmonella Typhimurium, and Listeria monocytogenes on fresh produce

Journal of Food Protection, Number 6, June 2014, pp. 872-1042, pp. 977-980(4)

Kim, Sang-Oh; Ha, Jae-Won; Park, Ki-Hwan; Chung, Myung-Sub; Kang, Dong-Hyun

http://www.ingentaconnect.com/content/iafp/jfp/2014/00000077/00000006/art00015

Because some companies are better at food safety; Martori adopts new food-safety program for cantaloupes

I can’t really assess whether these companies are actually better at food safety, but they’re willing to brag about it.

They get a balls-up from me.

cantaloupe.salmonellaTad Thompson of The Produce News writes that Martori Farms, headquartered in Scottsdale, Arizona, is fully activating a new type of food-safety program for packing cantaloupes.

The process, which employs a hot water shower to clean pathogens from the melons’ rough skin, looks to address critical food-safety issues that were ultimately related to the crevices in cantaloupe rinds

Stephen Martori Sr., president of the company, said his firm is one of two companies using this technology.

Martori built this hot water facility in its Aguila, AZ, packinghouse. Martori grows cantaloupes not only in Aguila but also in two other large farms, including one near Yuma, AZ. The firm is in the market seven months a year, shipping melons from May 1 through November.

The hot water shower was developed, beginning several years ago, through close cooperation with the U.S. Department of Agriculture’s Eastern Regional Agricultural Research Center in the Philadelphia suburb of Wyndmoor, PA. The research led to Martori’s system, which was commercially implemented in late April for the firm’s 2013 season launch.

The water shower lasts for approximately 20 seconds on each cantaloupe, which is rotated during the process. Targeting a water temperature of 162 degrees F, this brief hot water bath pasteurizes the skin, but is brief enough to avoid heating or injuring the cantaloupe’s flesh.

Martori Farms generally plans 1,000 in-house lab samples a season in its packinghouse. It has customers that want lab samples on the packingline of their specific orders.

In the peak of the coming Arizona cantaloupe season, Martori will pack more than 35,000 cantaloupes an hour, or approximately 400,000 melons a day.

“We are one of the largest melon grower-shippers in the country,” Martori said.

Cantaloupe accounts for 75 percent of the melon production at the firm, which produces more than 7,000 acres of melons, including 700 acres of watermelons.

Mini-watermelons and honeydew are also grown, packed and shipped by Martori. Among the honeydew offerings is its exclusive variety in North America, the Lemondrop.

In related news, Liberty Fruit Co. Inc. of Kansas City has earned the highest-possible food-safety rating, according to Scott Danner, the firm’s chief operating officer.

Danner said meeting the highest standards involves intensive training for all employees. He said all employees must pass individual tests for the correct food-safety protocols. Such questions may be as basic as, “What do you do if milk spills in the lunch room.” If someone in the organization doesn’t have the right answer, “We fail the audit,” said Danner.

Danner noted, “The hardest part of the process is to communicate with the rank-and-file. Without our loyal employees, we could not have done this. But they wanted to get involved.”

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

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.

lettuceIn 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.

Europe assesses the risk of Salmonella and Norovirus in leafy greens

Rainfall, use of contaminated water for irrigation or contaminated equipment are among the factors that cause contamination of leafy greens with Salmonella and Norovirus. These are some of the findings of EFSA’s latest opinion on risk factors that contribute to the contamination of leafy greens at different stages of the food chain. The BIOHAZ Panel has lettuce.skull.e.coli.O145recommended that producers use good agricultural, hygiene and manufacturing practices to reduce contamination. The Panel has also proposed specific microbiological criteria at primary production.

Leafy greens eaten raw as salads are minimally processed and widely consumed foods. Risk factors for leafy greens contamination by Salmonella spp. and Norovirus were considered in the context of the whole food chain including agricultural production and processing. Available estimates of the prevalence of these pathogens (together with the use of Escherichia coli as an indicator organism) in leafy greens were evaluated. Specific mitigation options relating to contamination of leafy greens were considered and qualitatively assessed. It was concluded that each farm environment represents a unique combination of numerous characteristics that can influence occurrence and persistence of pathogens in leafy greens production. Appropriate implementation of food safety management systems, including Good Agricultural Practices (GAP), Good Hygiene Practices (GHP) and Good Manufacturing Practices (GMP), should be primary objectives of leafy green producers. The relevance of microbiological criteria applicable to production, processing and at retail/catering were considered. The current legal framework does not include microbiological criteria applicable at primary production which will validate and verify GAP and GHP. It is proposed to define a criterion at primary production of leafy greens which is designated as Hygiene Criterion, and E. coli was identified as suitable for this purpose.

A Process Hygiene Criterion for E. coli in leafy green packaging plants or fresh cutting plants was considered and will also give an indication of the degree to which GAP, GHP, GMP or HACCP programs have been implemented. A Food Safety Criterion for Salmonella in leafy greens could be used as a tool to communicate to producers and processors that Salmonella should not be present in the product. Studies on the prevalence and infectivity of Norovirus are limited, and quantitative data on viral load are scarce making establishment of microbiological criteria for Norovirus on leafy greens difficult.

MIT phage-based bacterial detection for produce

Ever wonder why fruits and vegetables sometimes hit the shelves contaminated by pathogenic bacteria such as listeria, E. coli, and salmonella?

According to Tim Lu, an assistant professor of electrical engineering and biological engineering at MIT, it boils down to the inefficient bacteria-750px-PhageExterior.svgdetection assays used in the food industry. In some cases, these aren’t accurate or speedy enough — sometimes taking several days to catch contaminated produce.

But now Lu’s startup, Sample6, is commercializing an advanced assay platform that “lights up” pathogenic bacteria for quick detection, with the ability to detect only a few bacteria. 

Based on Lu’s graduate school research at MIT, the assay uses biological particles called bacteriophages, or phages, which only target bacteria. In Sample6’s case the assay is engineered to inject pathogenic bacteria — specifically, listeria — with an enzyme that reprograms the bacteria to shine very brightly.  

To use the commercial assay, called the Bioillumination Platform, factory workers simply swab samples with a sponge, wait for the phages to do their work, and run the sample through a machine that detects any light emitted. Results can be plugged into the company’s software, which tracks contaminated products and can provide analytics on whether contamination correlates with certain days, people, or suppliers.  

Careful with that poop; stricter controls of wastewater reuse on crops needed to meet WHO guidelines

Wastewater used to irrigate agricultural crops in countries where water is scarce may contribute to significant public health risks such as diarrheal disease in children from rotavirus. A new study of these risks found that wastewater used to irrigate vegetable plots in Asian countries poses health risks that may exceed World Health Organization (WHO) wastewater.veg.chinaguidelines. The authors recommend that stricter wastewater regulation may be needed to protect the health of farmers and consumers worldwide.

The new findings come at a time when climate change and increasing population pressure requires the development of methods to produce more food with fewer irrigation resources. Wastewater reuse is an economical method to grow food, but wastewater carries microorganisms such as viruses, bacteria and protozoa that can contaminate food and cause disease. Asia accounts for the majority of the world’s reuse of wastewater in irrigation, and given that China is the world’s most populous country, millions of people may be exposed to health risks from contamination. However, normal cooking temperatures and food preservation strategies can reduce the risks posed by microorganisms and viruses.

Although health studies can trace the incidence of disease in a population, conducting extensive experimental work and collecting sufficient data can be cost-prohibitive. Food systems researchers Hoi-Fei Mok and Andrew J. Hamilton of The University of Melbourne in Australia instead created a statistical model to characterize the health risks posed by wastewater used to grow Asian vegetables. The reach of the Asian vegetable market extends well beyond Asia. Their paper, “Exposure factors for wastewater-irrigated Asian vegetables and a probabilistic rotavirus disease burden model for their consumption,” recently appeared in the electronic version of the journal Risk Analysis, published by the Society for Risk Analysis.

The researchers first determined the volume of water retained by three commonly grown Asian vegetables, and then used a statistical model to estimate rotavirus disease burdens associated with wastewater irrigation. Rotavirus is associated with diarrheal disease in children, and was chosen as the focus of the study because diarrheal disease is associated with 74 percent of wastewater-related deaths, 90 percent of which occur in children. According to the WHO, diarrheal disease is the second leading global cause of death in children under five years old, and is responsible for the deaths of approximately wastewater.china760,000 children each year. Diarrhea can last several days, and can leave the body without the water and salts that are necessary for survival. Most people who die from diarrhea actually die from severe dehydration and fluid loss.

Based on their findings, the researchers concluded that the probability curves of the annual disease burden “exceeded the WHO’s threshold for acceptable level of risk from wastewater reuse by two to three orders of magnitude.” Some vegetables posed greater risk than others, because leaf shape affects the amount of wastewater and contaminants that are retained. Vegetables such as bok choy posed the least risk and choy sum the greatest risk, whereas lettuce and gai lan had similar risk profiles. The viral decay rate also varies depending on the plant. The authors say that more research on the rate of viral decay on various crops would increase the accuracy of risk estimations.

The probability of rotavirus infection is affected by uncertainty in virus concentration and variation in vegetable consumption. For example, the mean daily per capita lettuce consumption in Australia is 21.81 grams lettuce/person day, compared to a mean of 171.94 grams lettuce / person day in China, although there is seasonal variation in consumption patterns.

The dose-response model, which characterizes the relationship between exposure level to contaminants and the probability of developing disease, is a source of uncertainty in the risk assessment. The rotavirus infection rates were based on data from an infectivity trial in adults, but rotavirus primarily affects children. Lower doses induce infectivity in children faster than adults, so the estimated disease burdens from the researchers’ statistical model may underestimate the actual risk to children. Collecting rotavirus infectivity data for children would improve the accuracy of risk assessments of the threat.

Although there are Chinese national standards and regulations for the reuse of wastewater, they present only threshold concentrations for bacteria such as E. coli, not viruses. Furthermore, while there are regulations relating to water quality, there is no guideline for risk management around wastewater reuse in China. The risk management approach involves more pro-active identification and management of risk, rather than relying on post-treatment testing for managing reuse schemes. Considering the global increase in wastewater use for agricultural irrigation, assessing the health risks from reuse schemes is necessary to develop better wastewater management policies to protect public health. 

Prevalence of shiga-toxin producing E. coli, Salmonella enterica, and Listeria monocytogenes

There’s a lot of STECs out there.

Cooley et al report in Frontiers that, produce contaminated with enteric pathogens is a major source of foodborne illness in the United States. Lakes, streams, rivers, and ponds were sampled with Moore swabs bi-monthly for over 2 years at 30 locations in the vicinity of a leafy green growing region on the Central California Coast and screened for Shiga toxin producing Escherichia coli (STEC), Salmonella enterica, and Listeria monocytogenes lettuceto evaluate the prevalence and persistence of pathogen subtypes. The prevalence of STEC from 1386 samples was 11%; 110 samples (8%) contained E. coli O157:H7 with the highest prevalence occurring close to cattle operations. Non-O157 STEC isolates represented major clinical O-types and 57% contained both shiga toxin types 1 and 2 and intimin. Multiple Locus Variable Number Tandem Repeat Analysis of STEC isolates indicated prevalent strains during the period of study. Notably, Salmonella was present at high levels throughout the sampling region with 65% prevalence in 1405 samples resulting in 996 isolates with slightly lower prevalence in late autumn. There were 2, 8, and 14 sites that were Salmonella-positive over 90, 80, and 70% of the time, respectively. The serotypes identified most often were 6,8:d:-, Typhimurium, and Give. Interestingly, analysis by Pulsed Field Gel Electrophoresis indicated persistence and transport of pulsotypes in the region over several years. In this original study of L. monocytogenes in the region prevalence was 43% of 1405 samples resulting in 635 individual isolates. Over 85% of the isolates belonged to serotype 4b with serotypes 1/2a, 1/2b, 3a, 4d with 4e representing the rest, and there were 12 and 2 sites that were positive over 50 and 80% of the time, respectively. Although surface water is not directly used for irrigation in this region, transport to the produce can occur by other means. This environmental survey assesses initial contamination levels toward an understanding of transport leading to produce recalls or outbreaks. 

Pathogens in produce, Netherlands edition

The Dutch have decided to estimate pathogens in their produce in two Journal of Food Protection papers.

Prevalence and concentration of bacterial pathogens in raw produce and minimally processed packaged salads produced in and for the Netherlands

Journal of Food Protection®, Number 3, March 2014, pp. 352-521 , pp. 388-394(7)

Wijnands, Lucas M.; Delfgou-van Asch, Ellen H. M.; Beerepoot-Mensink, Marieke E.; van der Meij-Florijn, Alice; Fitz-James, Ife; van Leusden, Frans M.; Pielaat, Andannemarie

http://www.ingentaconnect.com/content/iafp/jfp/2014/00000077/00000003/art00006

Recent outbreaks with vegetable or fruits as vehicles have raised interest in the characterization of the public health risk due to microbial contamination of these commodities. Because qualitative and quantitative data regarding prevalence and concentration of various microbes are lacking, we conducted a survey to estimate the prevalence and contamination level of raw produce and the resulting minimally processed packaged salads as sold in The Netherlands. A dedicated sampling plan accounted for the amount of processed produce in relation to the amount of products, laboratory lettuce.skull.e.coli.O145capacity, and seasonal influences. Over 1,800 samples of produce and over 1,900 samples of ready-to-eat mixed salads were investigated for Salmonella enterica serovars, Campylobacter spp., Escherichia coli O157, and Listeria monocytogenes. The overall prevalence in raw produce varied between 0.11% for E. coli O157 and L. monocytogenes and 0.38% for Salmonella. Prevalence point estimates for specific produce/pathogen combinations ranged for Salmonella from 0.53% in iceberg lettuce to 5.1% in cucumber. For Campylobacter, this ranged from 0.83% in endive to 2.7% in oak tree lettuce. These data will be used to determine the public health risk posed by the consumption of ready-to-eat mixed salads in The Netherlands.

Microbiological risk from minimally processed packaged salads in the Dutch food chain

1.Mar.14

Journal of Food Protection®, Number 3, March 2014, pp. 352-521 , pp. 395-403(9)

Pielaat, Annemarie; van Leusden, Frans M.; Wijnands, Lucas M

http://www.ingentaconnect.com/content/iafp/jfp/2014/00000077/00000003/art00007

The objective of this study was to evaluate the microbial hazard associated with the consumption of mixed salads produced under standard conditions. The presence of Salmonella, Campylobacter spp., and Escherichia coli O157 in the Dutch production chain of mixed salads was determined. Microbial prevalence and concentration data from a microbiological surveillance study were used as inputs for the quantitative microbial risk assessment. Chain logistics, production figures, and consumption patterns were combined with the survey data for the risk assessment chain approach. The results of the sample analysis were used to track events from contamination through human illness. Wide 95% confidence intervals around the mean were found for estimated annual numbers of illnesses resulting from the consumption of mixed salads contaminated with Salmonella Typhimurium DT104 (0 to 10,300 cases), Campylobacter spp. (0 to 92,000 cases), or E. coli (0 to 800 cases). The main sources of uncertainty are the lack of decontamination data (i.e., produce washing during processing) and an appropriate dose-response relationship.