24 Oct 2011 Honey compound could fight foodborne pathogens
A Cornell University food scientist has identified an antimicrobial compound in a honey that makes it a promising candidate as a natural preservative to prevent foodborne illness and food spoilage.
Randy Worobo, associate professor of food microbiology at the New York State Agricultural Experiment Station in Geneva, NY, and members of his laboratory tested more than 2 000 strains of bacteria from eight types of honey from the US and New Zealand. One of them stood out.
“In sunflower honey from South Dakota, we identified a strain of Bacillus thuringiensis — the biological control known to organic gardeners as ‘Bt’ — that was effective against common foodborne pathogens, including Listeria monocytogenes, the bacteria behind the recent deadly cantaloupe outbreak,” Worobo said. “This Bt strain was intriguing because it had both strong antibacterial and strong antifungal activity.”
In analysing the compounds produced by the bacteria, the researchers found one with strong antibacterial activity that they designated as thurincin H. They recognised it as a bacteriocin, a common class of antimicrobials that bacteria produce to compete against other microbes.
However, compared with the some 40 known bacteriocins, it has something unique in that it is coded in the bacterial DNA as a unit containing three identical copies of the same bacteriocin gene.
The team’s findings were reported in September in Angewandte Chemie International Edition.
“This is the first report of a bacteriocin gene with this type of a triplet tandem repeat, and they are controlled by the same genetic on switch,” Worobo said. “This might partially explain the bacteria’s success against other microbes. It may allow the bacteria to rapidly produce large amounts of this compound.”
Not until Worobo collaborated with University of Alberta chemistry professor John Vederas did they discovery more unusual aspects of thurincin H. Using an array of techniques that give a three-dimensional picture of the molecule, Vederas noticed several unexpected properties.
“After the bacteria make the protein, it undergoes several enzymatic changes that determine the shape and rigidity of the molecule,” Vederas said. “Thurincin H forms four links between sulfur molecules and particular carbon molecules, which creates hairpins that are twisted into a helical structure. It’s actually the first time anyone has described a peptide with four of these linkages.”
The result is a molecule that looks like a rotary hairbrush with water-repelling residues on the outside. This combination of shape and function may allow thurincin H to infiltrate membranes of other bacteria.
The compound mimics the structure of the molecules that form bacterial membranes, which also have water-repelling residues on the outside, but it may disrupt those membranes by forming a rigid pore.
“The protein seems perfectly engineered to kill competing bacteria,” Worobo said.
This strain is effective against several strains of Bacillus, Listeria and Carnobacterium that cause foodborne disease or spoilage in food kept at improper temperatures as well as raw milk.
Now, Worobo and Vederas are exploring these unusual linkages and are working to characterise the mode of action of this unique peptide with the goal of developing thurincin H as an alternative to synthetic food preservatives, the Cornell announcement said.
“Bacteriocins are promising natural food preservatives for the food, livestock and agricultural industries,” Worobo said. “Because they come from food-grade microorganisms, they are generally regarded as safe.”
Source: FeedStuffs Foodlink