Photo of a man (Homayoon Davam, SLU) holding a white hen indoors in a poultry facility.
Homayoon Davam is a doctoral student in the project “Combating colibacillosis in poultry: measures to prevent outbreaks,” which runs from 2022 to 2026. Photo: Lisa Chröisty, SLU.

Vital or deadly, but when? Bacterial knowledge benefits farmers, society and poultry

Page reviewed:  15/09/2025

Bacteria exsist in all living bodies. Some are vital, others can cause illness and even death. But why do certain bacteria sometimes cause harm and other times not? That's what veterinarian and PhD student Homayoon Davam is investigating in a project on poultry and the well-known E. coli bacteria.

I have them, you have them, and most animals have them - E. coli bacteria are found in the intestines of all of us.

That’s how Homayoon Davam introduces the project to which he’s dedicating four years of his life. A project cantered on feathered animals, specifically, chickens. But the spotlight is shared with a bacterium that’s also well-known in humans: Escherichia coli (E. coli).

Although most E. coli strains does not cause any harm, there are some that can lead to serious illness and even death. In fact, E. coli infections are among the most common bacterial diseases in poultry worldwide, says Homayoon Davam. This affects not only the economy and food production, but also, of course, the health and welfare of the animals.

He continues:

So what we now want to find out is the big question: Is it possible to reduce outbreaks of E. coli infections in poultry—and if so, how can we do it?

Let's start from the beginning to find out: Is E. coli dangerous or not? And why only sometimes?

From Hatchery to Grocery Store Shelf – Sick or Healthy?

In the chicken industry, eggs are incubated in specialized machines, known as setters and hatchers, designed to create ideal conditions for embryo development, including optimal humidity and temperature. When the chicks are ready to see the light of day, the eggs hatch, and the little fluffy animals are moved, after necessary preparations, to larger facilities where they grow to full size over the following weeks.

At every stage of this process, we’ve observed that E. coli infections can emerge. But they don’t affect all animals—only some, and only sometimes—which makes it difficult to predict, hard to understand, and even harder to manage,” says Homayoon Davam.

In the first sub-studies, sick and healthy poultry are examined and compared. No animals are euthanized for the sake of the study—instead, sampling and post-mortem examinations are carried out on birds that have already died.

  • A comparison is made between two groups of poultry, all of which carry E. coli bacteria—yet only one group has fallen ill, while the other remains healthy. Samples are collected during necropsies of deceased birds, and droppings are gathered from the litter of those that appear healthy. The central question is: What distinguishes the disease-causing E. coli from those that do not cause illness?
  • Origin: Where do the bacteria that cause outbreaks come from, and when do they begin to cause disease? Do they originate from the parent birds, during the hatching phase, or while the chicks are growing on the farm?
  • Resistance monitoring where bacteria are examined for potential resistance to 15 different types of antibiotics.
  • Geographic mapping of where in the country the outbreaks are occurring.

In the final part of the PhD project, the data is supplemented with a survey to farmers. The aim is to gather additional information about management practices and the farm environment, and how these factors might influence the birds’ ability to develop a strong immune system or, conversely, increase their susceptibility to disease.

Therefore, E. coli from birds showing signs of illness is studied and compared with E. coli from birds that appear healthy. In addition, the goal is to gain a better understanding of when during the bird’s life these outbreaks tend to occur. (See more information in the menu above.)

What we know today about bacterial diseases in poultry is that they are multifactorial, meaning that several different factors influence whether or not the animals become ill.

Such factors may include, for example, the animals’ environment, the quality of care and management they receive, and the strength of each individual’s immune system.

What’s important to understand is that we can’t eliminate bacteria from animals entirely, bacteria like E. coli are necessary, says Homayoon Davam.: What we can do is work to reduce the number of disease outbreaks by learning when and why these bacteria sometimes develop into harmful infections.
Photo of a Petri dish with bacterial culture in a laboratory.
Bacteria. Photo: Lisa Chröisty, SLU

A detective for the Benefit of Society, Farmers, and Animals

Learning more about when and why bacterial diseases break out is important from several perspectives:

• For farmers, because disease outbreaks lead to significant economic losses.
• For society, since infected animals cannot be used for food production and must be discarded entirely—affecting the overall food supply.
• And of course, for the animals themselves, who are the ones to suffer the pain and consequences of illness.

Moreover, this is an issue that extends beyond Sweden’s borders, as E. coli is one of the most common causes of bacterial disease in poultry worldwide.

On top of it all, we’re also facing the growing challenge of antibiotic resistance, adds Homayoon Davam. More and more bacteria are becoming resistant to treatment, rendering antibiotics ineffective.

The focus, therefore, often needs to shift from treating diseases to preventing them.

And depending on how sick the animals are, it can be difficult to treat them with antibiotics—even in cases where the medication still works,” the PhD student explains. “That’s because antibiotics are usually administered through drinking water, and a sick bird may become too weak to drink enough, meaning it won’t receive an effective dose.”

In addition, even poultry that survive a bacterial illness are often negatively affected—they tend to grow more slowly, putting them at a disadvantage when competing for space and resources among the other birds.

Results on the Way

With just over two years of the project completed, Homayoon Davam has now reached the stage of preliminary results.

It was really exciting when we got the first results—clues that might help answer the why,” he says. “For a moment, you feel like a detective.

"I Always Dream Big"

There’s still just over a year to go before the project is completed and the results can be fully presented. But Homayoon Davam is already looking ahead, as he hopes to build a future where he can combine a career as a veterinarian with ongoing research:

When I previously worked on poultry farms as a veterinarian, I realized just how much more knowledge we need in many areas—and that’s exactly what we’re contributing to now.

The results of this study may also serve as a foundation for future research and could be used to better understand the transmission pathways of other bacteria as well.

Many of these bacteria are also highly capable of mutating, which makes it important to monitor their development closely—so that more of the bacterial diseases affecting poultry don’t begin to affect humans as well, says Homayoon Davam
Photo of a man (Homayoon Davam, SLU) wearing a lab coat working in a laboratory.
“For me, continuous development is important. I want what I do in life to matter,” concludes doctoral student Homayoon Davam. Photo: Lisa Chröisty, SLU

Facts:

  • The PhD project is funded by the Swedish Farmers’ Foundation for Agricultural Research (SLF) and is scheduled to run from autumn 2022 to 2026.
  • The doctoral student in the project is Homayoon Davam, working alongside a research group consisting of:
    • Ingrid Hansson, principal supervisor, veterinarian, and professor of Veterinary Bacteriology at the Swedish University of Agricultural Sciences (SLU).
    • Desirée Jansson, researcher in veterinary science with a focus on poultry medicine at the Swedish University of Agricultural Sciences (SLU).
    • Jesper Rydén, senior lecturer in BIOMETRICS (the application of mathematics and statistics in biology, environmental, and agricultural sciences) at the Swedish University of Agricultural Sciences (SLU).

 

The project can be easily divided into the following steps:

In the first sub-studies, sick and healthy poultry are examined and compared. No animals are euthanized for the sake of the study—instead, sampling and post-mortem examinations are carried out on birds that have already died.

  • A comparison is made between two groups of poultry, all of which carry E. coli bacteria—yet only one group has fallen ill, while the other remains healthy. Samples are collected during necropsies of deceased birds, and droppings are gathered from the litter of those that appear healthy. The central question is: What distinguishes the disease-causing E. coli from those that do not cause illness?
  • Origin: Where do the bacteria that cause outbreaks come from, and when do they begin to cause disease? Do they originate from the parent birds, during the hatching phase, or while the chicks are growing on the farm?
  • Resistance monitoring: Where bacteria are examined for potential resistance to 15 different types of antibiotics.
  • Geographic mapping of where in the country the outbreaks are occurring.

In the final part of the PhD project, the data is supplemented with a survey to farmers. The aim is to gather additional information about management practices and the farm environment, and how these factors might influence the birds’ ability to develop a strong immune system or, conversely, increase their susceptibility to disease.

Contact

  • Homayoon Davam, PhD student
    HBIO, Bacteriology, Virology, Food Safety and Veterinary Public Health