Salmonella enteritidis (SE) is the number one poultry-borne pathogen in the United States, and it can infect humans when they eat contaminated eggs. There is no fully effective vaccination for the pathogen. No researchers have used plant products to treat the infection where it starts, in chickens. Until now.
Working with collaborators, Kumar Venkitanarayanan, Professor of Food Microbiology and Safety in UConn’s Department of Animal Science, is trying to control SE in chickens with plant-derived, food-grade antimicrobials. His success so far has national importance in a country where people eat 50 million eggs every year and have increasing concerns about food safety.
National Poultry Science Association President Michael Kidd praised Venkitanarayanan’s work when he said it reflected “the very high quality and forward-looking nature of current poultry research, and its focus on improving the production, safety and quality of poultry products that reach the consumer.”
The four-year project, funded by the USDA, involves investigating the effectiveness and safety of specific antimicrobials by using them as chicken feed additives and disinfecting egg washes to control SE.
SE that is present in the intestines of birds can spread to their ovaries and contaminate egg yolks before shell formation. SE that is transmitted to the yolk in this way is the most difficult to control successfully, making it an important research objective. Solving the problem by adding a natural plant compound to chicken feed is a first, according to Venkitanarayanan.
Another part of the project is studying the same antimicrobials as egg washes because SE from the infected hens’ feces can get on eggshells after the chickens lay them.
With over $1 million in multiple grants funded by the USDA, Venkitanarayanan is hoping to reduce SE infection in birds, contamination in eggs and outbreaks in humans with safe and sustainable methods. He said, “We believe these plant compounds have a great potential in improving the microbiological safety of eggs without adversely affecting chickens and the environment.”
So far, the results are very promising. A solution to the problem can benefit the poultry industry where the annual economic loss from Salmonella-contaminated eggs is approximately $370 million. In addition, the research’s success is good news for people at risk of SE infections.
The public health risk
According to the Centers for Disease Control and Prevention website, healthy people infected with the Salmonella bacterium usually have fever, abdominal cramps and diarrhea for up to seven days. The illness may be more severe and cause death if left untreated in the young, the elderly and those with impaired immune systems.
A recent issue of Food Safety News reported that an August 2014 SE outbreak in the United Kingdom “sickened nearly 250 people, and three of them have reportedly died. And, according to public health officials, the illnesses can likely be traced back to a single source of eggs.”
Not all chickens are infected with SE and not all eggs laid by SE-infected chickens have SE in the yolk or on the shell. However, when SE is inside the egg, it is undetectable to the consumer. It could be present in Grade A eggs, even those with a clean, intact shell. The risk increases as eggs become more common in the average diet and are not cooked properly. Because eggs are an inexpensive source of protein and nutrients, they are widely consumed with each American eating an average of 270 eggs per year.
The food-grade, plant-derived antimicrobials used in the studies seem like things seen in the herb garden or spice cabinet. Some of them are found in food flavorings for human consumption. These compounds are readily available and effective in small amounts. They include trans cinnamaldehyde, an organic compound that gives cinnamon its flavor; carvacrol, which is present in the essential oil of oregano; thymol, found in oil of thyme; and eugenol, a liquid extracted from essential oils like clove oil and nutmeg. The U.S. Food and Drug Administration gives them the “Generally Recognized as Safe” (GRAS) designation, and Venkitanarayanan found no safety issues for chickens, poultry workers or the environment.
The researchers observed these compounds, in different combinations and concentrations, as feed supplements to see if they reduce the colonization of SE in the intestinal and reproductive tracts of chickens. In addition, the antimicrobials were used as egg washes to discover if they would kill SE on eggshells. Venkitanarayanan said, “This fundamental research showed that these compounds weaken Salmonella’s genetic mechanisms for colonization and spread in chickens.”
In one trans cinnamaldehyde supplement study on 40-week-old birds, SE was present in 40 percent of eggs from the control group while SE on egg yolks of infected eggs decreased to about a 3 percent level when the chicken feed was supplemented with a 1.5 percent concentration of the antimicrobial.
When Venkitanarayanan investigated similar ingredients as an egg wash, he reported that the compounds “were highly effective in killing SE on eggs compared to controls.” A 1.5 percent concentration of trans cinnamaldehyde reduced shell contamination of eggs to approximately 11 percent when compared to controls.
Venkitanarayanan believes, “An antimicrobial treatment that can be applied through feed represents the most practical and economically viable method for adoption on farms.” Therefore, the next step is field studies on farms.
Farmers, who have heard of the method through poultry conferences and Extension seminars, are already lining up to be included. Organic egg producers are especially interested. These GRAS washes and supplements could be a valuable tool for them as a sustainable practice. Venkitanarayanan is currently looking for funding for the next phrase of what promises to be an effective, natural solution to the SE problem in chickens and eggs.
At UConn, Venkitanarayanan works with Michael Darre, Professor in the Department of Animal Science, and Mazhar Khan, Professor in the Department of Pathobiology and Veterinary Science, on the project. Other collaborators include researchers from Auburn University, Pennsylvania State University, the University of Arkansas and USDA-Agricultural Research Service.
For a graduate student’s perspective, see http://naturally.uconn.edu/2014/07/23/meet-graduate-student-indu-upadhyaya/
By Patsy Evans