The most common intestinal infection, caused by the Salmonella bacteria

There is an infectious disease, caused by intestinal intoxication by a tiny bacterium, that infects more than 65,000 people each year in the European Union alone.

If not treated in time, this infection dehydrates the patient to such an extent that, although in fortunately rare cases, it can even lead to death from dehydration.

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We are talking about salmonellosis, which is the infection caused by intoxication by the bacterium Salmonella from the Enterobacteriaceae family.

Salmonellosis is one of the most common zoonoses in the world, and it is one of the major food hazards still present, plaguing contaminated foods, especially pork and eggs.

Read this page to find out what salmonella bacteria is, what salmonellosis is, how you get infected, what the symptoms are, and how you can treat it.

What is salmonellosis?

Salmonellosis is the infection caused by intoxication of the metabolic waste products of the bacterium Salmonella, a Gram-negative bacillus that is part of the large family Enterobacteriaceae.

Salmonella bacteria can survive with or without oxygen, and has its favored habitat in the intestines of animals, including humans.

All Salmonella bacteria are rod-shaped and have flagella, so they are able to move at will in their host's gut.

There are more than 2,000 types of Salmonella, but the ones that are dangerous to animals are about 50, including the serotypes of Salmonella typhimurium and Salmonella enteritidis, referred to as the 'zoonotic salmonellae'.

The serotypes dangerous to humans, once infected, expand rapidly in the host's gut, an environment particularly conducive to them, attacking nutrient residues and replicating uncontrollably, producing as metabolic material heterotoxins and cytotoxins, the real culprits in the violent immune system response that generates the symptoms of salmonellosis.

Zoonotic salmonellae are, along with intestinal viruses, the leading cause of food poisoning in humans.

What are the biological characteristics of Salmonella bacteria?

Salmonella is a facultative anaerobic bacterium, meaning that it can live both in the presence or oxygen and alternately without it.

It survives smoothly at room temperature within 20-30° C, but develops and reproduces even more easily between 37° and 40° C, which makes the human intestine a perfect place for its needs.

It is not killed by cold, only slowed down: it is still able to replicate at 7° C, while freezing sends it into stasis (stops its growth), but does not eliminate it.

Fortunately, both the bacterium itself and the enterotoxins that its metabolism produces are thermolabile, so they can be destroyed by high temperatures.

In fact, it is sufficient to raise the temperature to 70° C for at least 15 minutes to eliminate all bacteria, and inactivate the toxins they produce.

The pasteurization process also kills Salmonella, which is also destroyed by common disinfectants (alcohol-based or chlorhexidine).

Another characteristic now known to science for many years is the incredible antibiotic resistance of Salmonellae.

It is presumed that this resistance, which makes antibiotic therapies completely useless, began during the 1980s, starting with the serotype typhimurium, which first developed in exotic birds and from there, fairly quickly, reached mammals and humans.

Currently, more than 2,500 total serotypes of the genus Salmonella are known from two main species, Salmonella enterica and Salmonella bongori.

What is the life cycle of Salmonella?

Salmonella is a typical example of zoonosis, that is, an infection transmitted from animals to humans (and vice versa).

The bacteria can affect the intestines of many animals, both domestic and wild: birds (including poultry), rodents, felines, canids, cattle, sheep, horses, even domestic reptiles such as iguanas and turtles.

Salmonella hosts can be asymptomatic (healthy carriers) or manifest typical symptoms of intoxication, either in mild or severe form.

Usually, the human infection manifests itself in a mild or asymptomatic form, although there is no shortage of severe episodes, some even fatal (fortunately, the small minority), every year.

Transmission of the bacterium occurs exclusively via the fecal-oral route by ingesting food contaminated with animal (or even human) feces.

Salmonella is a serious health problem for industrialized countries because food contamination is almost always 'transparent': in fact, the bacteria does not usually cause visual or olfactory changes to contaminated food, making it very difficult to identify.

This happens because Salmonella cannot immediately expand into contaminated food and thus begin its cycle of metabolism, but when it succeeds, the production of hydrogen sulfide, the waste gas of bacterial fermentation, alerts it to food spoilage.

Once ingested during a meal, the bacterium resists the action of the stomach's gastric juices and, passing the duodenal valve, travels throughout the small intestine, beginning its fermentation and thus beginning to release its strong enterotoxins.

Following the path of the chyle, the food now absorbed by the intestinal villi, the bacterium passes the ileo-cecal valve and arrives in the colon, where it finds its perfect replication environment.

There the critical point of infection occurs, with massive release of cytotoxins.

The toxins cause violent irritation of the intestinal mucosa, with an equally violent response from the body, which attempts to defend itself against the infestation by the mechanisms of vomiting and diarrhea.

Symptoms usually begin about 12 to 24 hours after ingestion of the contaminated food, enough time for the bacterium to reach the gut and begin violently replicating.

Nausea, abdominal cramps, aerophagia and a strange feeling in the mouth, like 'rotten eggs' (the result of the release of hydrogen sulfide by the bacterium) appear.

These symptoms are followed by violent gagging, violent discharges of diarrhea, increasingly violent abdominal cramps and spasms, fever, and, not infrequently, even hallucinations.

After about 24 hours there follows a period of calm, with apparent remission of symptoms, but this does not last long: after another 24, diarrhea usually starts again, with the emission of yellowish, foul-smelling, extremely acidified stools.

Such acute diarrhea may last several days, and the diarrheal discharges may lead the patient to the danger of dehydration.

The infection resolves spontaneously after the body is able to rid itself, through diarrhea, of all the presence of the bacterium from the intestinal mucosa.

What are the symptoms of salmonella intoxication?

Salmonella intoxication varies considerably in symptomatology depending on the type of bacteria that has infested the intestine.

For humans, there are two types of Salmonella intoxication: typhoid fever, also called abdominal typhoid, and non-typhoid salmonellosis.

Nontyphoidal salmonellosis is common in both animals and humans, and is the most common and least dangerous form of Salmonella.

It manifests itself after a short incubation, between 12 and 48 hours after ingestion of the contaminated food, and begins with general discomfort, nausea, vomiting, emission of profuse diarrheal discharges, and high fever (38-39°C).

These symptoms last an average of a couple of days, but in some cases longer, and cease when the body has totally expelled both the bacteria and the toxins they produce.

The mortality rate of nontyphoid salmonellosis is extremely low, less than 1 percent, and the greatest risk during infection is that of excessive dehydration of the body.

Cases of septicemia or other infection localized to abdominal organs are extremely low, as is the risk of pericarditis or meningitis.

Typhoid fever is an infection that exclusively afflicts humans and is caused by Salmonella typhi and paratyphi intoxication.

It is definitely the most severe form of Salmonella infection, and manifests with progressive symptoms, the incubation of which can be as long as two or three weeks.

The onset is with high fever, 39-40° C, which is accompanied by extreme weakness, cough, abdominal pain (especially in the spleen and liver), and skin rash, with the appearance of pinkish spots on the abdomen and chest.

Diarrhea is a symptom that is not always present but is nonetheless common, and violent discharges can go so far as to injure the intestinal wall and cause episodes of rectorrhagia.

Cases of intestinal perforation are fortunately rare, about 1% or 2% of all infections.

During infection, due to the lowered immune defenses of the bacterium, opportunistic overinfection of the lungs by pneumococci is possible, which can give rise to pneumonia.

Typhoid fever is the only type of salmonellosis that has mortality rates above 10 percent if not treated promptly with antibiotic treatment.

What is the treatment for salmonellosis?

Nontyphoid salmonellosis, the most common and least dangerous form, is treated with symptomatic therapy.

Antiemetics or antidiarrheals should not be prescribed, as vomiting and diarrhea are the body's natural defenses that are implemented to eliminate the bacterial infestation, and therefore should not be hindered.

The greatest danger of infection is dehydration due to violent diarrheal discharges, and that is what therapy must address.

The patient must therefore be regularly hydrated, rebalancing the body's hydrosalinity.

This can be done with normal hydration by mouth or, in severe cases where vomiting prevents even drinking, intravenously.

Antibiotic therapy should be avoided at all times, at least for healthy adult individuals, because, in addition to not eradicating the bacterium, it also causes the death of the 'friendly' bacteria in the microbiome, whose survival is already challenged by Salmonella infection.

Typhoid fever, on the other hand, involves the necessary administration of antibiotic therapy, usually ceftriaxone, fluoroquinolone or azithromycin.

Again, appropriate supportive and hydrosaline rebalancing therapy must be combined with antibiotic therapy.

How can you GET Salmonella?

Salmonellosis is a major public hygiene problem, especially in settings where there is preparation of large amounts of food for large numbers of people.

Not surprisingly, salmonellosis outbreaks often have a communal canteen, restaurant or catering service as an outbreak.

All places where, although usually wordwide regulations on food control and preparation are stringent, contaminated food can always be present.

That being said, there are good behavioral norms to reduce the risks of contracting salmonellosis, and they are:

• Adherence to basic sanitation measures, such as washing hands thoroughly before each meal or even just handling food;
  
• The prompt refrigeration of food at temperatures below 7°C;
  
• Proper cooking of food with temperatures above 70° C for at least 15 minutes, especially poultry, pork and eggs;
  
• The avoidance of consuming raw eggs or undercooked foods;
  
• The avoidance of consuming foods such as mayonnaise (even industrially prepared mayonnaise) after a long time after opening the package;
  
• The avoidance of mixing cooked and raw foods in direct contact

It should be remembered that eggs are a preferred transmission vehicle for Salmonella bacteria, and that they are often the contaminated food that initiates the bacterial infection.

Salmonella bacteria can be present in any part of the egg: in the yolk, the albumen, but also in the shell.

That's why eggs should always be handled with care, always avoiding putting them in contact with other foods (even if placed in the refrigerator).

I think I have been intoxicated by Salmonella, who should I contact?

Nontyphoid salmonellosis is an extremely common intestinal infection, and any Physician is therefore able to diagnose it and propose the right palliative therapy to the patient.

If you think you are experiencing symptoms of Salmonella infection, you can turn as a first line of help to your Primary Care Physician, who is sure to be able to prescribe the right supportive therapy.

Typhoid fever, on the other hand, may require specialized diagnosis, special tests, and equally specialized therapies, which may lead to a mandatory visit to the Gastroenterologist or Colonproctologist.