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Salmonella Causing Cancer?

Posted in Salmonella on August 1, 2023

Could your stomach bug lead to cancer?  Researchers out of the University of Illinois, Chicago say yes.  A recent study led by Jun Sun, Ph.D. observed a link between Salmonella exposure and instances of colon cancer.


They found that colon cancer cases have developed earlier and generated larger tumor growth after even mild cases of salmonellosis, the illness associated with infection with the harmful bacteria, Salmonella.  Gallbladder cancer has also been linked to Salmonella infection in other studies.


What is Salmonella?

Most folks are familiar with the name SalmonellaSalmonella is a common bacteria that causes what is generally considered food poisoning or foodborne illness.  It is often associated with raw poultry, but can be found in many other foods sources that can make its way into our tables.



The Center for Disease Control and Prevention (CDC) estimates that the Salmonella bacteria is responsible for 1.35 million infections in the United States each year. While most people recover from Salmonella infection without medical intervention, each year 26,500 people require hospitalization and 420 die from this illness.



People often begin to experience symptoms of Salmonella infection anywhere from 6 hours to 6 days after becoming infected.  These symptoms often persist between 4 and 7 days.  General symptoms include diarrhea, fever, and stomach cramps, though some may experience more severe experiences, often due to dehydration that results from diarrhea.


Types of Salmonella

While there are more than 2,500 different known strains of Salmonella, they generally fall into two categories – Typhoidal Salmonella and non-typhoidal Salmonella.


Typhoidal are primarily limited to humans and responsible for severe systemic illnesses known as typhoid or paratyphoid fever.  The general mode of infection is fecal-oral, whereby some (even a microscopic amount) of infected fecal matter becomes ingested.  For this reason, typhoid fever and (para)typhoid fever cases are often seen in densely populated areas that lack access to improved sanitation.  In more modern areas, this can spread easily when poor hygiene and handwashing practices are observed.


The non-typhoidal Salmonella species are most common, with Enteritidis and Typhimurium (specific Salmonella strains) being the most common found in clinical patients.  Non-typhoidal Salmonella can infect a broad range of animals, including humans.


Non-typhoidal Salmonella infection occurs worldwide and are common in developed countries.  Infection often come from animals to human via food. But can result from direct animal contact or from the environment without proper handwashing.


What Gave Researchers the Idea to Investigate?

While digestive illness and colon cancer seem to have somewhat of a connection, it is a pretty big leap to guess that the two are related.  Dr. Sun and their colleagues were not just batting blind.


Another study from a Netherlands lab researching colon cancer patients often found Salmonella antibodies in tissue samples from those with poor oncological outcomes.


It also seemed that different categories of Salmonella bacteria affected different organs.  Systemic typhoidal Salmonella infections seemed to be linked to gallbladder cancer, whereas severe non-typhoidal Salmonella infections appeared linked to colon cancer.


But what was the link?  That is what Sun wanted to find out.


Let the Experiment Begin!

Dr. Sun’s team started with the same Salmonella strains found in the Netherlands study.  The first experiment used mice.  They infected mice with that strain and observed what happened.  What they found was scary!


Mice are usually employed as a first step in research because their bodies often respond similarly to humans.  For ethical reasons, researchers are unlikely to get support for infecting humans to study cancer occurrence.


They started by exposing mice to the same strain in the previous study.  Researchers found accelerated tumor growth and larger tumors in the mice exposed to Salmonella.


Next they moved on to human cells in vitro.  Dr. Sun’s team in Chicago collaborated with the Dutch scientists in the Netherlands.   The Dutch scientists combined both cancer cells and pre-cancer cells with the Salmonella bacteria and looked for changes.  The results were startling!


After just a single Salmonella infection, cancer cells were formed.  With each subsequent infection, the rate of cell transformation rose exponentially.


To further investigate this theory, researchers looked at samples from patients with colon cancer.  They took measurement of the amount of Salmonella in the affected tissues and compared that to bouts of infection in the test mice.  The results were spot on.  The lower amounts of Salmonella found in the organ, the smaller the tumors.  The higher amounts of Salmonella corresponded to an increased size of tumors.


This lead researchers to conclude that repeated Salmonella infection over the course of a lifetime can dramatically increase a person’s risk of developing colon cancer.


How Does a Bacteria Cause Cancer?

So how does Salmonella relate to cancer?  Turns out, it all comes down to how the bacteria infects its host.  The Salmonella bacteria hijacks essential signaling pathways in its host.


When the bacteria invades the cell, it injects over 30 different proteins into the host to help increase its ability to grow and thrive.  Some of these proteins are commonly known to affect cellular management; specifically, tumor-suppressing genes.


To test this theory, scientists modified the Salmonella activities that produced some of those proteins.  Certain suspect proteins were removed and researchers observed a significant reduction in the cell transformational effects of the bacterial infection.


Prevention is Key!

How do you help reduce your risk?  A healthy diet is always a good start.  But reducing your risk of foodborne illness could be a significant impact as well.


Proper Hygiene

Washing hands before and after cooking, after using the restroom, changing diapers, or other higher risk activities can significantly reduce the chances of becoming sick with foodborne illness.


Cook Foods Thoroughly

Use a kitchen thermometer to measure internal temperature of foods before serving.  Note that different temperatures are recommended for each type of food.



Store Foods Appropriately

Keeping high risk foods separate is a great step in food safety.  Never store raw foods near ready-to-eat foods.  Wash produce and store them appropriately.  Never use a cutting board or serving plate that previously held raw foods unless it has been carefully cleaned.


Keep an Eye Out for Recalls

We should be able to trust our food supply.  But sadly, sometimes things fall through the cracks.  Keep up with food recalls and safety announcements to help stay informed.


Stay Vigilant

Based on findings from several studies, it appears that there is a fair link between Salmonella infection and certain cancers.  Even more of a reason to stay vigilant with food safety.