What is the most complex organ in the human body? Most people would likely say the brain.
But a team of researchers at the Agriculture Canada Lethbridge Research Centre says it is the intestines, and that’s true of livestock as well as humans.
That’s why they are studying various aspects of bacteria interactions in the gut, and what they learn is expected to benefit the livestock industry and human medicine.
“Nothing is simple in the intestines,” said Doug Inglis, a senior research scientist at the centre.
“It is the most complicated organ in your body. I’d say it’s just as complicated, if not more, than the brain.”
A healthy intestine relies on bacteria and the body’s response to those bacteria, but that simple statement hides a complex interaction of mechanisms that Inglis and his team continue to explore.
“Our research takes what we call a biorationale based approach, so we really focus on the use of models to understand mechanisms and achieve innovations.
“We’re focused on intestinal health, so looking at control of enteric pathogens, as well as enteric inflammatory diseases, and ultimately we’re looking at developing efficacious non-antibiotic mitigation strategies.”
Those studies involve mice, chickens and pigs. An understanding of the complexities of those intestinal systems, and how they react to different bacteria, could also apply to humans.
Of course, humans often seek a simple cure for intestinal problems. Witness the popularity of foods containing probiotics, touted to improve or protect gut health. Inglis has a reaction to commercials for such products.
“I don’t laugh. I cringe. People are making a lot of money on products that really, there’s no proven efficacy. Nothing is simple in the intestine, and so when there is efficacy … the placebo effect can have profound impacts.”
Part of the research program in Lethbridge is focused on mitigating food-borne pathogens that also exist in animals. That requires researchers to work with clinicians to evaluate the significance of various illnesses in people.
The bacteria that gets the most media attention is E. coli 0157:H7, which exists without apparent effect in cattle, but can be fatal to humans. However, this nasty pathogen is not the biggest culprit in terms of public health.
That title belongs to campylobacter jejuni.
“It’s orders of magnitude (greater),” said Inglis. “More people get infected with campylobacter jejuni than E. coli and salmonella. It’s under the radar. It doesn’t cause recalls, so that’s a big thing … and also it doesn’t cause as severe morbidity in children.”
To put it in perspective, Inglis said more than 200 people are likely infected with C. jejuni each year, compared to 20 with salmonella and five with E. coli 0157.
But just how C. jejuni works within the intestine remains to be discovered. Researchers aim to develop strategies that can better protect public health against it “and also show that the industry is proactively addressing this issue,” Inglis said, in reference to livestock.
Where does the investigation begin? With a chicken.
Chickens and C. jejuni
Chickens are considered to be a reservoir for C. jejuni and rates of campylobacteriosis are considered high in southern Alberta. About half the cases occur in rural dwellers.
Nahal Ramezani, a veterinary microbiologist, is studying the pathogen at all points in the food chain. Over a one year period, she collected fecal samples from poultry in three southern Alberta broiler barns and a cattle operation, and skin samples from chicken at a processor and at a retail store.
She also collected bacteria from human diarrhea samples at Chinook Regional Hospital in Lethbridge.
Among the 11,240 total samples collected, she found campylobacter in about 5,000 of them. Not all types of campylobacter are pathogenic, so that result doesn’t necessarily ring alarm bells.
However, Ramezani’s tests show there is little diversity of C. jejuni among the chicken operations, and that bacteria from human diarrhea shared similarities with those in cattle and retail chicken samples. C. jejuni from chicken farms were not the same as that in human samples, indicating it was spread in another way.
Paul Moote, an enteric microbiology specialist, said most research looks at campylobacter as a species but Ramezani is examining it at the subspecies level.
“It’s important to know how the strains dominate the chicken because if you know the strains that dominate the chicken, you can figure out where those strains link to human health,” said Moote.
“You can figure out when are human pathogenic strains dominating chickens and how are they dominating chickens.”
Ramezani is also exploring the possibility that cattle are a reservoir of C. jejuni for chickens, so she is sampling cattle living next to a broiler site. The research could lead to mitigation strategies for disease prevention and control.
Chicken stress and illness
What causes stress in a chicken? There are many answers to that question, but one answer is Sarah Zaytsoff. She is studying the effects of stress on enteric diseases in chickens.
Starting with chickens that are as germ-free as possible, she puts a stress hormone called corticosterone in their drinking water to see how it affects the onset of illness and the composition of the birds’ intestinal bacteria.
“I’m specifically looking at clostridium perfringens. It causes necrotic enteritis in chickens, which is quite impactful and often results in sudden death,” said Zaytsoff.
To determine the effects, she examines the metabolic genes in the birds’ liver and also analyzes their intestinal tissue to see if there is a change in nutrient uptake.
She found that stress significantly increases the amount of C. perfringens in chickens, affects their immune response and likely has an impact on feed efficiency, which has implications for producers.
“Notably, all of the birds that received stress treatments showed significant reduction in weight gain, which can be relatable to production setting where many runty birds can be found,” she wrote in a summary of her research.
C. perfringens can infect humans, though its effects are limited. In chickens, however, it damages the small intestine and can be fatal.
How do you get a germ-free chicken, or at least one that is as germ-free as possible?
That is Kaylie Graham’s area of expertise.
The University of Lethbridge student and research assistant is developing ways to rear chicks that have simple microbial communities. Limiting the types of bacteria present in the chicken, and knowing what types those are, allows researchers to study those types and how they interact with bacteria they may want to introduce.
“It allows clearer observation of colonization and interactions between bacteria species,” said Graham.
What about mammals?
It is a challenge to study specific bacteria when there are so many types in the intestine and their precise relationship to one another is unknown.
That makes it impractical to work with large mammals at the bacterial level.
Maximo Lange uses germ-free mice, which were initially raised elsewhere, delivered by caesarean section and then put into sterile environments so exposure to particular bacteria can be isolated and monitored.
“These are excellent models to study mechanisms. Since you don’t have any other bacteria, you can introduce the bacteria you are studying and you will only isolate or analyze or study that one bacteria in the mouse,” said Lange.
His research focuses on E. coli 0157:H7, a pathogen that has forced food recalls because it can cause severe human illness. Cattle are the main reservoir, although it causes them no apparent health effects.
“We’re trying to study how it colonizes cattle, what actually happens in there and why it colonizes, how can it survive, what kind of mechanisms it uses to survive. By using these simple models of germ-free mice, we’re trying to see exactly how it behaves,” said Lange.
“The intestinal location of this bacteria in ruminants is still debatable and unclear, as well as the colonization mechanisms…. The aim of our project is to use germ-free mice as a ruminant intestinal model in order to study in detail the different mechanisms that this organism utilizes to survive in the intestine.”
There are many different types of E. coli in the normal ruminant intestine, so unless researchers can start with either bacteria-free or known types of bacteria, it is im-possible to isolate and study E. coli 0157:H7.
Inglis said there are no effective strategies for mitigating the deadly bacteria in cattle. A vaccine has been designed to combat it but it is costly and not completely effective. That indicates the need for further research.
“There’s some stuff out there that says (E. coli 0157:H7 is) in the very distal colon/rectum, but I don’t think it’s that simple. I think it’s going to be colonizing other components of the intestine and that’s what these models allow us to do.”
Using mice as a substitute for cattle or pigs has been criticized, said Inglis, but he doesn’t see a problem.
“This is the exact strategy people use for human medicine,” he said.
“If you can use a mouse for a human model, why can’t we use it for a pig model? We’ve spent a lot of time convincing the producers that our strategy is valid, and now I think they’ve come around to accepting it.”
Pigs and their parts
Porcine epidemic diarrhea (PED) has killed millions of piglets in the United States and Canada in the last three years. The disease harms the pigs’ intestines so they cannot properly absorb nutrients, and they die of starvation and malnutrition.
Moote’s research could lead to creation of probiotics tailored to colonize and protect injured intestinal tissue and suppress viral and bacterial infection.
But first, Moote must learn how and why certain bacteria cause intestinal inflammation and then identify other bacteria that mitigate or heal that same inflammation.
“My work would look at finding bacteria that are associated with the inflammation associated with PED. If you can have less harmful bacteria that can colonize that inflamed tissue and assist in the redevelopment of non-inflamed tissue, you could potentially prevent PED because PED requires a certain amount of inflammation to exist,” said Moote.
“If you can take an organism that can go into the piglets that can suppress the inflammation, even if there is stress, you could hopefully reduce the availability of tissues for these viruses and other pathogenic bacteria to colonize.”
Salmonella infection is another example where Moote’s research could apply.
Those bacteria can dominate the microbiota in a pig’s intestine. Tissue becomes inflamed and the salmonella feeds on that tissue. If that salmonella could be blocked, “you could potentially reduce the risk of enteritis in piglets and in hogs,” said Moote.
“And that’s really critical because enteritis in piglets is a big issue, a big, big issue. So we’re hoping to find bacteria that can help displace salmonella.”
He has created a collection of bacteria, some isolated in the presence of salmonella and some in its absence. These could be used to develop an effective probiotic.
As well, he is studying how pigs fight off salmonella, which drastically reduces the diversity of bacteria in the intestinal tract. Over time, however, pigs regain their microbiota as they mount a defence.
“You could really assist in developing unique tools to mitigate salmonella infection by providing or stimulating some of those defence mechanisms,” said Moote.
“It’s critical that we can find the bacteria that are actually associated with displacing salmonella because they are either displacing it by competing with the actual bacteria, or they are assisting the host. Those are two different, distinct mechanisms.”
While Moote studies changes in microbiota, Danisa Bescucci is studying the way bacteria in the host, in this case a pig, respond to inflammation in the intestine.
“If you were to stimulate a host response that’s not going to hurt the host but prepare it, then when you go to wean or you lose that maternal antibody, then you can have your treatment,” said Bescucci.
For example, there might be a protein that can stimulate certain cell growth and prevent or fight inflammation.
Bescucci hypothesizes that the cecum, a part of the pig’s intestinal tract between the small and large intestines, produces short chain fatty acids that resist harmful bacteria. If that proves out, research specific to the cecum could lead to reduced bacterial infection.