Understanding Salmonella and its Effects on the Gut Microbiome
Summer is (unofficially) salmonella season: with warmer temperatures, consumption of more raw produce, and food being left outside longer during meals, salmonella can multiply rapidly to the point where it causes infection. Small can be mighty. Just two species, Salmonella bongori and Salmonella enterica, salmonella infection is one of the four leading causes of diarrhea worldwide1,2. In fact, while many of us have experienced a relatively mild case of food poisoning that was likely due to salmonella contamination, the bacteria are responsible for millions of deaths per year2.
Salmonella is named after Dr Daniel E. Salmon, a veterinarian who discovered their existence in pigs, along with researcher Theobald Smith3. Notoriously hardy, these bacteria are able to withstand prolonged exposure to both dry and water environments1. Salmonella is commonly found in the intestinal tracts of farm animals, including pigs, cows, and chickens. Because the bacterium is passed by the fecal-oral route, livestock manure becomes the perfect breeding ground for salmonella transmission2. If it is not cleared from livestock areas, it can infect other animals – and if farm workers are not careful about their own exposure to contaminated animals and manure, salmonella can be transmitted to them as well.
How Salmonella Causes Foodborne Illness
Because of the widespread infection of farm animals, the consumption of animal products is the most common method of infection for individuals1. Even eggs can be contaminated by salmonella as the bacterium can infect the ovaries of chickens. However, outbreaks from fresh produce like spinach are also seen and are likely due to salmonella contamination of manure applied to ground crops1.
Salmonella’s hardiness in the environment is also mirrored by some remarkable adaptation when they reach the human gut: salmonella attacks the intestinal lining, which causes the human immune system to fight back with oxygen radicals that are meant to kill microbes. However, those oxygen radicals are thought to form a compound called tetrathionate in the gut, which fuels the growth of salmonella4.
Salmonella: Possible signs and symptoms
Symptoms don’t appear right away, making it sometimes difficult to pinpoint the source of contamination. Salmonella symptoms typically appear 12-36 hours after ingestion of the bacterium; they include diarrhea, nausea, fever, and abdominal pain1-3. These symptoms are usually mild and last 2-7 days, however, in young children and the elderly, associated dehydration can be dangerous1-3.
As with all foodborne illness, salmonella infection can have a lasting impact – digestive symptoms may persist for months, or transform into a post-infectious irritable bowel syndrome. This occurs because of digestive tract damage, as well as the impact of infection on resident gut flora. However, it is also thought that a healthy and robust intestinal microbiota may actually confer resilience in the face of foodborne illness5. The reason for this is that our gut flora, or microbiota, is naturally competitive. When you have a strong and diverse intestinal flora, it competes for space and nutrients with any ingested bacteria, making it more difficult for them to gain a foothold.
Gut bacteria also directly fight harmful microbes in many ways, including with the short chain fatty acid propionate, which has been found to inhibit the growth of salmonella5. Probiotics are a common strategy to support a healthy gut flora alongside a high-fiber diet; interestingly, one animal-level trial suggests that some probiotic strains may help mitigate the impact of Salmonella infection in the gut6.
Prevention: Stay safe, eat safe
Salmonella infection is common – but it’s also simple to prevent. It’s all about keeping things clean, cooked and chilled. Always thoroughly wash any produce item meant to be eaten raw – even prewashed items as these have been subject to previous salmonella outbreaks. Avoid unpasteurized dairy. Cook all raw animal products such as eggs and meat thoroughly and keep them at temperature at all times. Keep chilled items chilled and minimize the length of time that cooked or chilled items are kept at room temperature; after two hours (or one hour in hot weather), it is recommended that you compost any food that has been left out.
When travelling, avoid consuming water or ice cubes that are not from verified sources – and stick to cooked food in high-risk tropical locations. Taking a probiotic like Bio-K+ is a great way to support gut health and immunity while travelling. The other piece of the puzzle is maintaining excellent hand hygiene. Always wash hands before and after handling food, eating, touching public surfaces and using the washroom. Avoid touching your face in public places to limit the potential for oral exposure to salmonella.
What to do if you suspect food poisoning
Because salmonella infection typically resolves on its own, rest, hydration and electrolyte replacement are the common treatment1. However, in the uncommon instance where antibiotics are prescribed, it’s important to reinforce your intestinal flora using a clinically proven probiotic such as Bio-K+. Bio-K+ has been shown effective and is Health Canada indicated, for prevention of the side effects of antibiotic use, including antibiotic-associated diarrhea.
Salmonella is common – and preventable. This summer, as you enjoy your fun in the sun, be sure to keep it clean. And if you think you have a foodborne illness, it’s important to seek medical attention – particularly for young children and the elderly. Your doctor will be able to confirm your diagnosis and ensure that more serious infection isn’t present; however, taking the time to see your doctor will also improve surveillance and disease control outcomes.