Salmonella: What is it? How to Take it, Salmonellosis Symptoms and Treatment

Salmonella: What is it? How to Take it, Salmonellosis Symptoms and Treatment

Salmonella and Salmonellosis

Salmonella is a genus of bacteria responsible for one of the most common gastrointestinal infections in industrialized countries: salmonellosis .

For humans, the risk of contracting this disease is mainly associated with the ingestion of contaminated food during storage and handling. Foods of poultry origin, especially eggs and derivatives, and pork are a frequent cause of salmonellosis.The severity of the symptoms of Salmonella infections varies from simple gastrointestinal tract disturbances ( fever , abdominal cramps , vomiting and  diarrhea ) to more severe clinical forms, which occur mainly in people already debilitated by other diseases.


What is Salmonella?

Salmonella is the most commonly isolated bacterial agent in foodborne infections . Salmonellosis ( Salmonella infection ) is, in particular, one of the food poisoning infections .

Salmonella is commonly found in the intestines of healthy birds and mammals .

Food poisoning or food poisoning?

FOOD INFECTIONS are caused by the ingestion of foods contaminated by various pathogens.

  • If the disease is caused directly by the presence of an often high number of microorganisms in a food, we speak of food poisoning ;
  • When it is due to the toxins produced by the germs in the food, on the other hand, we speak of intoxication .

Intestinal viruses and Salmonella are the most common agents of toxin infections; the most frequent intoxications , on the other hand, are those due to toxins from the Staphylococcus aureus and Bacillus cereus bacteria . On the other hand, Clostridium botulinum deserves a separate discussion, responsible for the most serious (but fortunately not frequent) food poisoning : botulism. Food and drink can promote the transmission of other infectious diseases, including: cholera , viral hepatitis type A, typhus and paratyphoid.

Salmonella: characteristics of the infectious agent

The term Salmonella identifies a group of Gram negative bacteria (i.e. negative for Gram staining), which fall within the Enterobacteria family . Therefore, these are microorganisms that find their ideal habitat in the intestines of reptiles, birds and mammals, including humans.

Bacteria of the genus Salmonella are rod-shaped and motile due to the presence of flagella . They develop well both at room temperature and inside the human body, but do not tolerate high temperatures and acidic pH (values ​​lower than 5.5).

Salmonella is sensitive to chemical and physical agents If it occurs at temperatures below 5°C, refrigeration prevents bacterial multiplication, without killing the microorganisms. Freezing , on the other hand, causes a moderate inactivation of Salmonella , as well as preventing its growth.

Cooking food drastically reduces the risk of infection, since the bacteria are destroyed by the heat. The main host-dependent risk factors for salmonellosis are reduced gastric acidity , disturbance of the normal intestinal bacterial flora , and concomitant malignancy or inflammatory enteric disease .

Among the numerous serotypes – around 2000 – in which Salmonella can be distinguished, the most dangerous variants for humans are “only” about fifty. The serotypes Salmonella typhimurium and Salmonella enteritidis are the most frequently found in humans and animals (in particular, poultry), therefore they are considered ” zoonotic salmonella “.

What is Non-Typhoidal Salmonella?

As far as humans are concerned, as anticipated, there are several bacteria of the Salmonella genus capable of causing infectious diseases, but they are not all equally “aggressive”.

The main Salmonella infections affecting humans can be divided into two large groups:

  • On the one hand we have the most serious TYPHOID FORMS , such as typhoid and paratyphoid fever ;
  • On the other hand there are the NON-TYPHOID FORMS , called minor salmonellosis .

Typhoid fever and paratyphoid are quite serious diseases caused by the bacteria Salmonella typhi and Salmonella paratyphi . These infections only affect humans and are widespread above all in developing countries, while they are rare in Italy and other industrialized countries.

Non-typhoidal Salmonellae or ” minor Salmonellae ” are, however, more common. In these cases, the manifestations are usually confined to the gastrointestinal level; moreover, the responsible bacteria are not a prerogative of man, but also involve many animals, including those bred for food.


Salmonella: causes

The main reservoirs of infection are wild, domestic or farm animals , such as chickens, pigs, cattle, rodents, dogs, cats and chicks. These eliminate Salmonella in the external environment with feces , contaminating food derived from them, feed and water.

Salmonellosis is therefore considered a zoonosis , i.e. an infection that can be transmitted from animals to humans .

For humans, food is one of the most important sources of contagion .

Food can be contaminated with Salmonella due to the fact that:

  • Comes from an infected animal (example: meat , eggs and milk consumed without prior effective heat treatment);


  • Has come into contact with faecal material from infected animals or people.

Risky foods

  • Raw (or undercooked) eggs and egg-based derivatives (  raw egg -based sauces or creams );
  • Meat and derivatives (especially raw or undercooked poultry);
  • Fish , crustaceans, molluscs;
  • Unpasteurized products (e.g. raw milk and raw milk derivatives);
  • Fruits and vegetables (watermelons, tomatoes , seed sprouts, melons, lettuce, unpasteurized cider and orange juice), contaminated during cutting;
  • Preparations for cakes, creams, homemade and commercial ice cream.

Notes : generally, food contaminated with salmonella does not show organoleptic alterations (colour, smell, taste , texture).


Salmonellosis affects over 90,000 Europeans each year, but the incidence is currently on the rise in almost all industrialized countries.

This trend can be explained on the basis of several elements, such as:

  • Selection of antibiotic-resistant strains ;
  • Import of meat and livestock with introduction of Salmonella serotypes from other areas;
  • Diffusion of intensive farming;
  • Greater use of collective catering.

For these reasons, in order to try to limit the increase in cases, it is important to adopt precise rules of a preventive nature.

Contagion and Risk Factors

How do you get Salmonella?

Salmonella is a microorganism normally present in the gastrointestinal tract of many animal species, from insects to mammals. Salmonellosis in animals frequently runs without clinical signs , but they are “healthy carriers” of the bacterium.

So how does the bacterium get into the human stomach ? Salmonella infection is caused by three main vehicles of transmission: food , water and small pets ; in all cases, if one of these comes into contact with the feces of an infected animal, it becomes contaminated in turn.

Food contamination can occur:

  • At the time of production and preparation;
  • After cooking, due to incorrect handling (e.g. touched with dirty hands or utensils).

Salmonella infection is more common in the summer months (June, July and August) than in the winter .

Faecal-oral transmission

The Salmonella infection is transmitted via the fecal-oral route , therefore whenever the bacterium somehow manages to reach the oral cavity of a healthy individual from the feces of an infected animal. Salmonella can therefore be contracted through the ingestion of food or drink contaminated , directly or indirectly, by the faeces of infected animals or people.

The most frequent causes of Salmonella toxin infections are:

  • Irregular and incomplete cooking of the food;
  • Cooling too slow;
  • The poor hygienic conditions of those who handle food.

In particular, cross-contamination is frequent, for example between raw and cooked foods, or between meat and vegetables; this contamination occurs as a result of handling and storage errors, for example using the same utensils to process raw and already cooked foods.

Contagion is facilitated by the fact that food contaminated by Salmonella does not have abnormal odors or tastes and therefore does not arouse suspicion.

Direct contact

Salmonella can also be contracted by contact, i.e. by handling contaminated objects or infected animals For example, it is sufficient for a person with a small hand wound to inadvertently touch the faeces or saliva of a pet (cats, dogs, birds, iguanas, turtles, etc.) that are carriers of salmonellosis.

Salmonella: where is it?

Salmonella is most frequently found in foods such as eggs, mayonnaise , unpasteurized milk , poultry , pork, hamburgers , fish and shellfish grown in contaminated water.

Risk factors

  • Eat raw or undercooked seafood
  • Do not wash your hands after handling uncooked food, animals or faeces
  • Consume unpasteurized milk
  • Do not store food carefully, for example storing eggs and egg products at room temperature
  • Food handling by infected people
  • Alteration of the intestinal microbial flora
  • Gastrectomy or medications to reduce stomach acid
  • Inflammatory diseases and intestinal neoplasms
  • Immunosuppression
  • Recent use of antibiotics or corticosteroid therapy
  • Children under 5 and the elderly
  • Overcrowding and poor hygienic conditions

Symptoms and Consequences

How does Salmonellosis manifest itself?

Salmonellosis manifests itself with a set of disorders that can have different intensity and seriousness depending on the case.

The severity of the disease also depends on the virulence of the infecting serotype , the number of ingested microorganisms ( bacterial load ), the factors of resistance to the infection and the health conditions of the host .

In particular, low levels of gastric acidity favor the engraftment and proliferation of pathogens, with the consequent appearance of diarrhoea. In other words, if the bacteria are not neutralized by stomach acid secretion , the body responds with another defense mechanism to eradicate the pathogens; that defense consists of the unpleasant but helpful diarrheal discharge. Subjects treated with proton pump inhibitor drugs, for example for reflux problems or peptic ulcers , could therefore be more exposed to the risk of salmonellosis.

Healthy people are able to better counteract the action of Salmonella, especially when the infection is contracted orally and the amount of contaminated food ingested is small, therefore they may have mild symptoms. In the opposite situation, i.e. when one is exposed to large quantities of Salmonella (even by contact) and the body is debilitated, salmonellosis is more likely to occur and can also be of high intensity from a symptomatological point of view.

Salmonella: what are the symptoms?

Primary Salmonella infection , ie with exclusive localization in the gastrointestinal tract (called ” minor salmonellosis “), causes gastroenteritis ; only in the most serious cases does it cause septicemia with extra-intestinal manifestations (arthritis, osteomyelitis, pneumonia, meningitis, endocarditis, etc.).

Salmonella typically causes :

  • Nausea ;
  • Crampy abdominal pains ;
  • Diarrhea with loose stools mixed with mucus and sometimes small amounts of blood .

It is also possible the presence of:

  • Green feces ;
  • Fever (38-39°C);
  • Vomiting ;
  • Joint pains ;
  • Headache .

    Symptoms Salmonella: after how long

    Normally, the symptoms of salmonellosis appear after about 12-72 hours after ingestion of contaminated food or, in any case, after exposure to the bacterium. This short period is the so-called incubation time , during which Salmonella reproduces in the intestine.

    Invasive Salmonella infections

    Children, the elderly and particularly debilitated subjects can accuse more serious clinical pictures and extra-intestinal manifestations, such as: pneumonia , endocarditis and pyelonephritis .

    If Salmonella manages to migrate into the bloodstream, it can cause bacteraemia or focal infections of, for example, the bones and meninges .

    Possible consequences of these invasive variants of salmonellosis include:

    • Meningitis (infection of the membranes lining the brain and spinal cord );
    • Osteomyelitis (bone infection);
    • Septic arthritis (infection of a joint).

    Mortality from salmonellosis is extremely low; more at risk are newborns and infants, the elderly and those already debilitated by other diseases, such as AIDS patients .

    How long does Salmonellosis last

    The intensity of the symptoms described above varies, but salmonellosis generally resolves within 4-7 days. Serious systemic forms can affect subjects at risk such as newborns, the elderly, the immunosuppressed and make hospitalization necessary.


    Salmonella: how is it diagnosed?

    The diagnosis of salmonellosis is confirmed by stool culture ( stool culture ). The analysis allows to highlight the presence and identify the serotype of Salmonella at the origin of the infection.

    In severe forms, the isolation of the microorganism can also result from blood, urine or exudate cultures.

    Treatment and Remedies

    Salmonella: how to cure it

    Since it is a bacterial infection, it would be natural to think that salmonellosis can be cured with antibiotic treatment. In reality, the use of antibiotics is often not recommended because, in most cases, Salmonella gastroenteritis is a mild and self-limiting form , so the symptoms regress spontaneously within a few days.

    For this reason, the main therapeutic measure is represented by rest and a generous intake of liquids , useful to compensate for the water and salts lost through vomiting and diarrhea.

    The administration of lactic ferments and probiotics is also very useful to reconstitute an optimal bacterial flora.

    Antibiotic therapy is reserved only for elderly or immunosuppressed subjects, for children under two years of age and in general for severe infections, with extra intestinal symptoms.

    Apart from these cases, an unjustified antibiotic treatment, in addition to being useless, could contribute to drug-resistance phenomena.


    How to prevent Salmonellosis

    Salmonella infections can be avoided by practicing some simple hygienic precautions. These include the correct handling of raw foods, especially those of animal origin, which includes:

    • The prompt refrigeration of food;
    • Periodic washing of hands and surfaces such as cutting boards and dishes;
    • The separation of raw meats from other foods;
    • Cooking food at the correct temperature.

    To decrease the risk of salmonellosis, it is recommended to wash your hands before, during and after preparing food.

    Cooking foods derived from animals well, especially poultry, pork and eggs, reduces the risk of infection, since the bacteria are destroyed by heat. It should be remembered, however, that Salmonella can contaminate tables, hobs, cutlery and dishes, and then be transferred from one food to another during the preparation phases. For this reason, the sterilizing effect of the cooking heat is canceled if, for example, the knife used to cut raw meat is used shortly afterwards to cut cooked meat or raw vegetables ready to eat .

    Equally dangerous is the habit of breaking the eggs, underestimating the potential infective load of the shell. For this reason and to avoid bacterial cross-contamination, raw foods should be separated from cooked foods.

    Salmonella Temperature Killing

    To destroy any Salmonella present, it is possible to cook the food, in all its parts, at 70°C for at least a quarter of an hour (note: if it has already formed, the heat does not make the toxin labile).

    Salmonella: some practical tips to avoid it

    • Always wash your hands with soap and water:
      • Before you start cooking
      • Before eating
      • Before and after touching raw foods
      • After handling the trash
      • Before cleaning work surfaces
      • After touching pets and cleaning their cages/kennels
    • Do not consume raw or undercooked meat, eggs and poultry . Also pay attention to foods that contain raw egg-based sauces or creams (mayonnaise, tiramisu, eggnog , etc.).
    • Use gloves if you have wounds or injuries on your hands .
    • Do not consume eggs with broken or dirty shells . Do not buy broken, dented or swollen packages, discolored products or frozen with frost. Always check that the drinks have not been exposed to the sun or other sources of heat.
    • Regularly check the conditions of foods stored in the refrigerator and keep eggs and all fresh foods (mayonnaise, creams, sauces) at 4°C, preferably consuming them as soon as they are prepared, without keeping them for long.
    • Avoid cross-contamination between foods by keeping raw and cooked meats separate and thoroughly washing all utensils used to handle raw food. Protect partially eaten or cooked foods with plastic wrap or place them in airtight containers to prevent contamination.
    • Before consumption, wash fruit and vegetables , to eliminate any presence of microbes and residues such as pesticides; avoid this operation before putting the vegetables in the fridge, as the increase in humidity favors the growth of mold and bacteria.
    • Clean the refrigerator often with a clean and disinfected sponge also moistened in a little vinegar or a specific detergent .

    Salmonella and eggs

    To contain the risk of contracting salmonellosis from handling eggs, in addition to the already existing prevention measures, attention should be paid to:

    • When breaking the shell, try not to break it, in order to avoid small pieces ending up in the yolk or albumen ;
    • Throw the remains of the shells in the trash, avoiding placing them on work surfaces or putting them in contact with kitchen utensils;
    • At the end of these operations, always wash your hands with soap and water.


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