Probiotic bacteria thickens coat | Researchers hope to develop strain to reduce food poisoning in humans
LINDELL BEACH, B.C. — British researchers have discovered that a strain of probiotic bacteria in poultry can change its coat to fight a pathogen that causes necrotic enteritis in poultry and is one of the most common causes of food poisoning in Britain, the United States and Canada.
It is now known that the gastrointestinal tract of poultry is a major reservoir of bacteria that causes food poisoning.
The problem bacteria, clostridium perfringens, colonizes the gut of chickens. The probiotic lactobacillus johnsonsii has adapted the thickness of its coat to combat the colonization of C. perfringens.
Results of the study from the Institute of Food Research in Norwich, U.K., have been published in the online journal PLoS ONE.
According to the report, scientists had previously isolated and characterized lactobacillus johnsonsii from the gut of a healthy chicken that had the capacity to exclude pathogens from the gastrointestinal tract of poultry.
This discovery could potentially improve poultry welfare and reduce levels of human food poisoning bacteria from meat products.
“At the moment, we know how the coat is made and which genes are involved, but what regulates the expression of the genes involved is not confirmed,” said Arjan Narbad, research leader with the IFR.
“We suspect there may be environmental cues that may trigger the regulatory genes to reduce or upregulate the biosynthetic pathways for production of the coat.”
The entire genome of the L. johnsonsii bacterium has been se-quenced, which has helped scientists better understand the processes of competitive exclusion used at the molecular level.
The bacterium actually changes its coat by making it smoother. Narbad called this special coat a slime capsule, which completely surrounds the bacterium and gives it the definitive smooth texture.
“The coat is made up of two different types of what we call exopolysaccharides, which are large molecules made up of a combination of different sugars,” said Narbad.
“We have now established the detailed structures of these coats and one of them is quite novel. The coat provides a number of functions, such as protection against drying when outside the host and providing resistance to antibiotics.
“The coat also protects from the harsh acidic condition in the stomach, for example, and also against bile salts in the small intestine so it can reach the large intestine unharmed where the bacteria can attach and colonize.”
The natural appearance of the smooth coat may also be a deliberate variation in its population to take advantage of environments that may be colonized by pathogens.
The discovery came about by accident. One of the researchers in Narbad’s group was growing bacteria on petri dishes. The bacterial colonies have a large and rough morphology in appearance, but she noticed that a small proportion of them were much smaller and looked smoother.
“Initially we thought these small colonies were contaminants,” he said. “However, when we performed DNA fingerprinting on these small colonies, we discovered that they were all the same lacobacillus johnsonii as the ones that had large rough colony morphology.
Further investigation indicated that it was coat thickness that changed the colony morphology.
“We are still some way away from understanding the regulation of the coat production,” said Narbad.
Research has focused on the one strain of bacteria that is of greatest concern, but studies are being planned to see if the coat alteration responds differently in the presence of different kinds of pathogens.
“We have not tested the response of the bacteria to different pathogens, but it is something that we are looking at currently,” he said.
“Now that we have sequenced the entire genome of the probiotic strain, we can examine the changes in expression of all the genes under different conditions.”
Researchers want to see how they can affect potential pathogens by genetically manipulating the coat gene. The technology transfer company Plant Bioscience Ltd. will help put the probiotic strain through large-scale farm trials to assess its efficiency.
PBL is a technology management company in the U.K. specializing in plant, food and microbial science that underwrites the studies and draws a share of revenues once a product becomes commercialized.
“The strain is being produced in large volumes using pilot plants that would generate sufficient product for evaluation of its effectiveness under farm conditions,” said Narbad.
“If these farm trials are successful and the product is licensed, then the bacterial production would be scaled up for eventual commercialization.”
