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Researchers Combine ‘Luck and Guesswork’ to Find Salmonella’s Achilles’ Heel

A sugar and amino acid compound called fructose-asparagine never previously recognized as a nutrient for any organism is the stuff that makes Salmonella grow and it could be key to the pathogen’s demise. Brian Ahmer, associate professor of microbial infection and immunity at The Ohio State University, says the nutrient may be the Achilles’ heel for Salmonella and its 2,500 strains.

It’s the single food source Salmonella need to remain strong inside the inflamed intestine. Blocking the activation of one of five genes that move the nutrient to Salmonella cells could be the way to fight the infection. That’s because when they are blocked and the Salmonella cannot get access to this nutrient, they becomes much times less effective at keeping the disease going than when fully nourished.

For some reason, Salmonella really wants this nutrient, and if it can’t get this one, it’s in really bad shape,” says Ahmer, commenting on the research recently published in the peer-reviewed, open-source journal PLOS Pathogens. The single nutrient, known as F-Asn, opens new pathways for fighting Salmonella because it opens up a weakness not previously seen in the pathogen that has long confounded science.

“If you could block Salmonella from getting that nutrient, you’d really stop Salmonella,” Ahmer explains.

Foods such as raw meat and raw eggs contaminated with Salmonella bring on Salmonellosis, a disease of the intestine. Symptoms usually occurring in 12 to 72 hours include diarrhea, fever, cramps, vomiting and headaches. Usually the illness last four to seven days, requiring only home care.

However, Salmonellosis can require hospitalization. In rare cases, usually where the infection moves to the bloodstream from the intestine, it can be a cause of death. Salmonella has been a perplexing problem for both industry and government in the U.S. The Centers for Disease Control and Prevention (CDC) says that Salmonella causes 1.2 million illnesses, 23,000 hospitalizations, and 450 deaths annually in this country.

Risks from Salmonella are greater in underdeveloped countries where poor sanitation conditions exist.

Because antibiotics kill both helpful and harmful bacteria, they are not usually used to treat Salmonellosis. The new research raises the possibility of making a drug to target the genes needed to acquire F-Asn to impede Salmonella growth while not impacting other gut bacteria.

Scientists originally looked at five genes required by Salmonella for life during the active phase of gastroenteritis. They found the five worked together to move a nutrient into the bacterial cell and then broke it down for use as energy.

Ahmer says it took “luck and guesswork” to see the links with genes in E. coli and to identify the nutrient as F-Asn.

The researchers then experimented on cell cultures and mice to find out what happened when the genes were mutated. They found that Salmonella’s fitness to “survive, grow, and inflict damage” fell by 100 to 10,000 times if it was not able to gain access to the nutrient even when other sources of food were available.

“Nobody’s ever looked at nutrient transporters as drug targets because it’s assumed that there will be hundreds more transporters, so it’s a pointless pursuit,” Ahmer says. “That was one of the big surprises: that there is only one nutrient source that is so important to Salmonella. For most bacteria, if we get rid of one nutrient acquisition system, they continue to grow on other nutrients. In the gut, Salmonella can obtain hundreds of different nutrients. But without F-Asn, it’s really unfit.”

They may have reached this finding with the help of guesswork and luck, but several questions still remain that will require hard work to answer. Future research from the team will examine the window of time in which access to F-Asn is most important for the bacteria’s survival. They will also investigate which human foods contain high levels of the nutrient.

For now, though, the authors say that the F-Asn utilization system represents a specific and potent therapeutic target for Salmonella.

The National Institute of Allergy and Infectious Diseases and the National Institute of General Medical Sciences supported the research with grant funding.

Co-authors include Mohamed Ali, Christopher Stahl, Jessica Dyszel, Jenee Smith and Yakhya Dieye of microbiology; Juan Gonzalez, Anice Sabag-Daigle and Brandi Steidley of microbial infection and immunity; Judith Dubena, Prosper Boyaka and Steven Krakowka of veterinary biosciences; Razvan Arsenescu of internal medicine, and Edward Behrman of chemistry and biochemistry, all at Ohio State; Peter White and the late David Newsom of the Research Institute at Nationwide Children’s Hospital, and Tony Romeo of the University of Florida.

Food Safety News

Good growing weather, bad buying weather combine for depressed markets

One California shipper said it a “classic example of beautiful weather out here (California) combining with terrible weather in the East to produce cheap low markets.”

David Cook, sales manager for Deardorff Family Farms, Oxnard, CA, said “we have had gorgeous weather for weeks on end. It seems our winter came during a two week period in early December and it has been beautiful ever since.”

He said that has led to better than usual supplies and East Coast movement that is down a bit because of the terrible weather.

Concurring was Mark McBride, who sits on the sales desk for Coastline in Salinas, CA. “The last 10 days we have hit 70 degrees with no rain or cold. These are ideal growing conditions. Coupled with the Arctic Vortex and all the other storms in the East that are resulting in schools closings and white outs everywhere, we are seeing demand disrupted and shipments delayed.”

On Tuesday, Jan. 21, McBride said he expects the supply exceeds demand situation to remain in effect until normal weather patterns return to both coasts. As he was speaking to this reporter, the Los Angeles area was basking in 80 degree temperatures with lots of sunshine, while New York City was 18 degrees with snow showers. “Anytime you have the two halves of the country doing that, we are not going to have good markets,” he said, quipping that the reverse is what causes good markets.

McBride said cauliflower prices were fairly good for the first two weeks of the new year, but by the third week they had dropped down to the $ 10 f.o.b. mark, which still created a high spot on the sales board. Many other staple items, including iceberg lettuce, romaine, leaf items, celery and broccoli were selling well below the double digit level into deep red number territory.

One of the few strong items was peppers, which are mostly coming from Mexico through Nogales, AZ, at this time of the year. Mike Aiton, marketing manager at Prime Time Sales LLC, Coachella, CA, said cold weather early in the Mexican growing season has delayed heavy production of peppers. He added that cold weather in Florida also hampered production of peppers from that region. “Usually we are not sending a lot of peppers to the East Coast at this time of year but this year we are,” he offered.

Aiton does not expected a big jump in volume until early February and even then, the strong market could continue, especially for the colored peppers. He explained that because of the lack of green peppers and the good market for that product during most of January, a lot of growers were harvesting their colored peppers while they were still green to capitalize on the high prices. Consequently, the volume of the reds, yellows and oranges will probably lag behind a bit once volume picks up.

Cook said strawberries were one item that seemed to be taking advantage of the good weather to produce good numbers and a good market. January is always an iffy month for California producers as cold weather and rain can often impact the new crop. But the aforementioned warm weather was producing some beautiful berries with a market in the $ 18 to $ 20 range.

Baja California, San Diego, Orange County and Oxnard are the points of origin for West Coast berries this early in the season and all four areas were experiencing good weather and good supplies. “I expect the market to stay in this range through Valentine’s Day,” said Cook.

That holiday always creates a good pull for berries, especially stem berries which can return a very good price for shippers. “After Valentine’s Day, volume should pick up and we will probably see the price start to come down,” said Cook.

Decreased supplies of Florida strawberries also were having an impact. Cook said supplies from Florida appeared to be lighter than usual at this time of year.


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Agrofresh calls to combine efforts to reduce Asia fruit waste problem

Agrofresh calls to combine efforts to reduce Asia fruit waste problem

With accumulative post-harvest supply chain losses of 30% in Asia*, the General Manager for AgroFresh EMEA & ASIA, Peter Vriends, is calling on the industry to improve its partnerships and lift its investment to overcome the storage and supply chain barriers to deliver more high quality fruit.

Speaking at the Business Forum at Asia Fruit Logistic, Mr. Vriends said that planning, investing, controlling and partnering were the ‘ingredients’ to reducing dramatically high fruit losses in Asia and achieving sustainable fruit quality. “Our fruit losses currently compare very badly with the United Kingdom and Europe (18%), and while we may seek to excuse or rationalize these on the basis of hot and humid climatic conditions in some regions, we should not be losing so much fruit and potential revenue,” he said.

Mr. Vriends said that in blocking ethylene, SmartFreshTM 1-MCP, the technology pioneered by his company, was playing a valuable part in maintaining post-harvest fruit quality.  Although now marketed in over 40 countries, and the only globally recognized and registered 1-MCP product, he strongly insisted that the solution to fruit waste was not a matter of using only cold storage and SmartFresh. “The solution to fruit losses lies in a combination of planning, investing, controlling and partnering across the supply chain. There is no silver bullet or single solution when you lose 8% at storage, a further 8% a distribution and another 15% at retail and in the consumer’s home.

Fresh produce losses at retail and at consumer level in Asia were up to five times higher than those of the UK. Mr Vriends said that research conducted in the Netherlands by A.C. Nielsen Retail showed the use of SmartFresh 1-MCP resulted in a 25% overall reduction in shrinkage and a 12% increase in sales during the 10-week test period. This involved 24 Dutch supermarkets, with 12 selling apples stored with SmartFresh, and 12 with non-SmartFresh apples of the same variety. Mr Vriends shared with the Forum some new research from Thailand on the benefits of using SmartFresh with mango.

“Comparing SmartFresh treated fruit with untreated, we measured the percentage of rotten fruit in ambient temperatures over a 29 day period. Within 20 days 100% of the untreated fruit was rotten and unmarketable.  At 29 days only 30% of the SmartFresh fruit was rotten and 70% was in better condition than the untreated fruit at 15 days ambient. This reinforces the way in which reducing fruit waste is a prize worth pursuing.”

For more information:
Yvonne Harz-Pitre, PhD, Head of Global Communications
Tel: + 33 149217879
Mobile: +33 675086597  
email: [email protected]

Publication date: 9/17/2013