Has Salmonella got you down? Try some yogurt!

After spending an eternity in the restroom in pain, you decide to explore how to prevent it from happening again. Luckily, significant research has been performed on a common bacteria living inside that raw meat product you consumed before your unfortunate trip to the bathroom. The likely culprit—Salmonella.

Salmonella is a pathogenic bacteria that has been found to cause 1.35 million cases of foodborne illness every year in the United States alone [1]. The average amount of time for Salmonella-induced food poisoning is a couple of days after symptoms arise [1]. The most common symptoms that occur when your gut is infected are vomiting, nausea, and diarrhea.  

Consulting a doctor is recommended if you have pre-existing health problems like irritable bowel syndrome or if symptoms persist for more than a week [1]. Age can also play a role in how Salmonella impacts your body [1]. Children, elderly, and immunocompromised people are prone to worse symptoms than healthy middle-aged people [1]. The first step in symptom prevention is recognizing the ways that Salmonella can enter your body. 

The pathogen can rapidly colonize the gut microbiome in many different ways. In pursuit of an explanation for the bacterial infection, Dr. Sztein from the University of Maryland’s School of Medicine has delved into analyzing red blood cells, white blood cells, and other common immune cells by probing human fecal matter (yes, it is gross). The internal cellular conditions were tracked using an epigenetic marker, a beacon in the DNA coding, to determine how gene activity in immune cells were impacted in the presence of Salmonella [2]. The researchers also color-coded each cell type with a staining process called 33-metal-labeled monoclonal antibodies to follow the respective cell types they wanted to observe [2]. This streamlined staining process allowed Dr. Sztein to observe the different immune cells using mass cytometry; this efficiently labeled antibodies with heavy metal tags altogether instead of using individual staining [2]. After tracking the cell types through their epigenetic markers and color coding, all of the tested cell types were found to be negatively affected by the pathogen through either loss of cell function or targeted elimination [2].

Despite the ill-effects of Salmonella caused in human cells, the bacteria ironically originates in other animal cells. Warm-blooded farm animals naturally carry Salmonella hidden away in their intestines and can be spread during the butchering process [3]. It is the classic example of more than “meats” the eye, where raw meat products are nothing but bacterial-ridden hosts waiting to infect you if not properly cooked. 

The pathogen seems to make its way through many sources. The Centers for Disease Control and Prevention (CDC) has highlighted the main ways Salmonella can be spread throughout the environment, including the consumption of raw meat products like chicken, beef, pork, and lamb [1]. The pathogen likely enters livestock through the ingestion of feed contaminated with animal fecal matter, allowing it to thrive in the gastrointestinal tract [1,3]. Salmonella is passed onto humans when we consume an infected animal without properly cooking the product [1]. Due to the high temperatures, the process of cooking the animal kills off the pathogens making the food safe [3]. Additionally, fecal matter may also poison poorly filtered water sources, causing yet another opportunity for humans to contract Salmonella [5].

Salmonella bacteria can also be found in more than just raw meat and water. Cross-contamination between food and infected humans can create a haven for the pathogen in the grocery store [7]. Cross-contamination happens when people do not wash their hands thoroughly after touching fecal matter or other Salmonella-laced items (as seen in Figure 2). The CDC keeps a record of every major outbreak of Salmonella when food is recalled by a manufacturer [8]. Recalled products, due to contamination from the adventurous pathogen, range from the aforementioned raw meat to seafood, dairy, fresh produce, peanut butter, and even Kellogg’s Honey Smacks cereal [8].

Recently, there has been a significant effort to prevent the adverse effects on the body. Mia Potočnjak's research team from the University Rijeka has investigated three species of probiotics, Lactobacillus plantarum A, L. plantarum B, and L. plantarum S1, of the genus Lactobacillus to help prevent the colonization of Salmonella in the gut and keep it healthy [9]. This genus of bacteria is a type of probiotic typically found in milk-containing products such as yogurt and kefir (drinkable yogurt). Probiotics are living microorganisms that support a healthy human microbiota by defending against pathogenic bacteria and helping with digestion. Probiotics do this by supplementing the “good” bacteria naturally present in the gut [10]. What normally accompanies probiotics in food products is prebiotics. Prebiotics serve as a food source to stimulate the growth and/or activity of bacteria that are present in your gut to improve the human microbiome [11]. The main difference is that probiotics are alive microbes while prebiotics act as a substrate to provide nourishment to the microbes [10,11]. Keeping the gut microbiome healthy is important because it has been found to promote positive mental health and can help prevent other types of bacteria from growing inside your body [12]. 

 Researchers have found that all three of the Lactobacillus species help create a protective slippery layer around the colon tissue [9]. The researchers employed an adhesion assay, which utilizes human intestinal Caco-2 cells from a cultured medium via an in vitro tissue culture plate [9]. Researchers slathered copious amounts of probiotics onto the intestinal cells on the tissue and then introduced other bacteria to the sample to view how well they “stuck” to the cells [9]. With an inverted microscope, Potočnjak’s team found positive results when they observed the three Lactobacillus species had adhered well to the cells and were successfully able to compete against Salmonella T. for the adhesion sites [9]. This finding validates that probiotics prevent harmful Salmonella bacteria from sticking to intestinal tissue and colonizing the gut microbiome. Like fighting fire with fire, Lactobacillus bacteria wield metaphorical extinguishers to protect against Salmonella infection by snuffing colonization and inflammation stemming from the gut.

Next time you travel down your local grocery store's dairy aisle, remember it is important to pick the right yogurt that suits your needs. Stay away from top yogurt companies that riddle their products with added sugar and natural flavoring [13]. Salmonella strains thrive in high-sugar environments because it is a good food source for them [14]. Top yogurt companies also lack probiotic supplements, which negates one of the main health benefits of yogurt. Consider local small companies, though slightly more expensive, that have less sugar, and more often than not, have added healthy probiotics like the Lactobacillus species to help coat your gut [13]. 

Smaller companies are also more beneficial for the health of their consumers because they derive their products from grass-fed animals [15].  Grass-fed yogurt contains less omega-6 fatty acids and more omega-3 fatty acids than normal cow yogurt. This suggests benefits to the heart and gut because of the positive link between omega-3, which also improves brain and gut function [15,16]. Grass-fed yogurt is rising in popularity because cows and sheep eat a more natural diet, so contamination is less prevalent because the livestock do not consume shipped-in feed that could be contaminated with Salmonella [15,17]. Another type of yogurt containing beneficial bacteria, that can also be grass-fed depending on the brand, is greek yogurt. Greek yogurt is rising in popularity because it is strained twice during production to remove the liquid and whey [13]. This leads to double the protein and half the sugar, reducing the majority of Salmonella’s food source in the final product [13]. With more local products like grass-fed yogurt hitting the market, the option for healthier and less contaminated products is becoming more available [15].

Consuming grass-fed yogurt products, or locally sourced Greek yogurt, that contain the three Lactobacillus strains can coat your gut in “good bacteria” and prevent the colonization of Salmonella. If you lack the microbial resources to protect your microbiome against Salmonella infection, you will be more susceptible to inflammatory changes in all cell types present in your gut. Most symptoms do not last long but be wary because you may end up in the restroom again, wondering to yourself why you didn’t pick up any grass-fed Greek yogurt containing Lactobacillus at the grocery store yesterday. 

 

About the Author: Scott Ellison

Scott Ellison is a 4th-year Medical and Molecular Microbiology major who fell in love with microbiology through the television show Bones. He wants to pursue a career consisting of traveling the world collecting samples for either NASA’s or NOAA’s Biology Departments. Food poisoning is deeply rooted in Scott’s family because when he was younger his grandmother got into a car accident due to food poisoning symptoms. Scott believes being mindful of what you consume and how it impacts your gut microbiome is a necessary step in preventing illnesses like Salmonella infections. 

References

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