Escherichia coli bacteria (E. coli) are common to the bacteria flora found in the large intestines of humans and other mammals. Most of these bacteria are harmless, while others can cause serious illness to humans. This happens when E. coli adhere to the intestine, which may cause diarrhoea. If the bacteria also produce the poisonous Shiga toxin, it may lead to renal failure and in some cases death of the affected individual.
E. coli bacteria in food may cause grave illness. (Photo: Shutterstock)
Different measures for different bacteria
In recent years, several serious outbreaks of E. coli have occurred in Norway. Finding the source of infection has proven difficult or even impossible.
Identifying the source of infection poses a major challenge for many countries.
“Individual groups of bacteria exhibit distinct behaviour and must be approached in different ways,” explains Anne Margrete Urdahl, a researcher working with E. coli-outbreak emergency planning at the Norwegian Veterinary Institute in Oslo. “That’s why it’s so crucial to find out quickly which subgroups of E. coli we are dealing with whenever an outbreak occurs.”
Transmitted from animals
“Greater knowledge about E. coli bacteria has enabled us to develop faster methods of isolating the bacteria of interest in a sample containing many types of bacteria,” explains Urdahl.
“E. coli bacteria can also be found in animals, but does not usually render them ill. Nevertheless, people can become infected via contaminated meat products, through direct contact with animals or animal faeces as well as through vegetables, milk or water,” says the researcher.
The Norwegian researchers have put considerable effort into mapping the occurrence of E. coli in sheep. “We are trying to find correlations between the properties of bacteria found in animals and bacteria that cause disease in humans. This will help us to determine the degree of risk that a certain type of bacteria in animals actually poses. The problem is very complex and various factors come into play,” says Urdahl.
Anne Margrete Urdahl (Photo: Norunn K. Torheim)
To find out what distinguishes pathogenic bacteria from their more benign cousins, the researchers create DNA profiles for the bacteria in the same way that police investigators produce DNA profiles to identify people.
New diagnostic tools save time
“Previously, we had to spend several days working with a large number of samples to determine if they contained a target subset of pathogenic E. coli. Then we had to check whether the bacteria had the ability to produce the toxin and adhere to the intestine,” says Urdahl.
“A recently developed method has helped us to cut down significantly on the number of samples. This has improved our turnaround and we can now dispel or confirm suspicions about the sources of infection far more quickly.”
The researchers have been mapping the occurrence of E. coli in sheep. (Illustrative photo: Shutterstock)
The new method uses tiny magnetic beads to identify subgroups of E. coli. Different beads bind to respective subgroups of the bacterium and are isolated from the sample using a magnet. A colour reaction indicates whether these bacteria have become bonded to the beads.
Researchers have also adopted methods that cut down on the time needed to find bacteria groups known to contain specific genes.
Viruses alter the properties
Another challenge has been to investigate whether viral infection can alter the properties of E. coli bacteria.
“It is well established that bacteria can obtain new genetic material from viruses. This may furnish bacteria with the genetic material needed to produce the toxins that make them more virulent and harmful to humans than before. Our findings confirm this for some of the bacteria those we are working with,” says Urdahl.
Risk posed by biofilm
One source of bacteria in food is from biofilms that develop in facilities in food industries. A biofilm is an aggregate of many different types of microorganisms tightly packed together on a surface, encased in a self-produced layer of slime. This protects its contents from desiccation, disinfectants and the like, and they can survive in this state for a long time.
“Our project has also researched the properties of isolated E. coli bacteria in biofilms,” explains Urdahl.
The ability of bacteria to form biofilm is tested on various substrates and at different temperatures. Here we see E. coli biofilm on steel at 20° C and on glass at 12° C. Colour has been added to the biofilm to make it easier to see. (Photo: Heidi Solheim, Veterinærinstituttet)
“We have found that E. coli from sheep can form biofilm at temperatures and on surface materials well-suited to food production. Additionally, we now know more about how easy it is for different types of E. coli to survive in food-production facilities.”
Still, the researchers are unable to provide clear guidelines on the types of surface materials to use in food production, as biofilms are formed by different bacteria on various types of surfaces and at different temperatures.
Disinfectants of the future
The researchers have also investigated whether bacteria can receive genes from viruses in biofilm.
“We now know that biofilm is one place where E. coli bacteria can infect each other with viruses that makes them more dangerous to humans. This is important new knowledge about how harmful bacteria can arise. The results of the project show that blocking the formation of biofilm in food-production facilities may help to keep food from becoming contaminated with pathogenic bacteria.”
The researchers have a clear idea of how to accomplish this: “In order for bacteria to form biofilm, they must cooperate with each other, and to cooperate, they need to communicate. If we manage to block this communication, we can prevent bacteria from forming biofilm in facilities where food is produced.
Biofilm is one place where E. coli bacteria can infect each other with viruses that makes them more dangerous to humans. (Photo: Norunn K. Torheim)
“We are currently testing whether communication can be blocked using substances called furanones. These substances were originally isolated from a type of algae. We have tested variants synthesised at the University of Oslo, and we see that they have some effect. Substances of this type may become the ‘disinfectants’ of the future,” hopes Urdahl.
Of international importance
“These findings help to resolve key long-term challenges to Norwegian food industries. But the thematic areas of safe food and a sustainable supply chain are very much a global challenge. This research is therefore also of importance in an international context,” says Maan Singh Sidhu, senior adviser of the Research Council of Norway’s Food Programme, under which this research was partially funded.
|About the project|
Researcher Anne Margrete Urdahl of the Norwegian Veterinary Institute is heading the research project “Public health aspects and the relationship between Shiga toxin-producing and Enteropathogenic E. coli in the ruminant food production chain,” which has been granted funding under the Food Programme of the Research Council of Norway.
Scientific research partners: Norwegian School of Veterinary Science, the Norwegian Institute of Public Health, the University of Oslo and Nofima Mat.
Industry research partners: Norwegian Independent Meat and Poultry Association, Tine BA and Norgesgruppen.