What is listeriosis


What is listeriosis

Listeriosis is an infection caused by the bacterium Listeria monocytogenes which can occur in pregnant women, infants, and patients with compromised immune systems (such as elderly, AIDS sufferers, diabetics, etc.), can be serious or difficult to control in many cases.

Listeria monocytogenes is a bacterium of the Group of Gram positive bacilli, i.e. is elongated and is stained with Gram stain purple, lipoteichoic acids, involved in the virulence of the Microbe has on its outside wall. About your body have flagella that function as propellers so that the bacteria can move at room temperature.

This microorganism owes its name to Joseph Lister, English physician of 19th century implanted the conditions of asepsis and antisepsis in surgery, greatly reducing mortality rates. This scientist is not the discoverer of the bacteria, although it was the name of Listeria in his honor.

Is spread Listeria monocytogenes

Listeria monocytogenes is found in a multitude of sites. Fresh water and waste water, soil, vegetation, pets, etc.

However, the main mechanism of transmission to humans is ingestion of the bacterium directly; Therefore, Listeria monocytogenes is dangerous when it is in food. Outbreaks of listeriosis cases are always associated with the consumption of food, most of the time packaged, which were contaminated by the bacterium in question (sausages, cheeses, smoked meats, unpasteurized products). Since a person ingests Listeria until it develops the disease it can take two to six weeks, making it difficult to identify exactly what was the food that was contaminated.

On the other hand, it should be noted that the Listeria monocytogenes does not produce disease in healthy humans, only affects immunocompromised by mechanisms which we explain later. In fact, can analyze samples from the intestine of a healthy person and see there are Listeria monocytogenes without involving any problem.

What is listeriosis

When we talk about the causes of Listeria must point to the bacterium Listeria monocytogenes, which enters our body when we eat it. Upon reaching the intestine, it comes in contact with the enterocytes (cells that line the intestine wall inside) and goes inside. Thereafter the bacteria can pass cell in cell without ever being in the external environment.

When this happens in healthy people it has greater impact because Listeria is isolated in the intestine and is not dispersed by the body, but when it happens in a person with cell-mediated immunity low bacteria is able to circumvent these weakened defences and cause infection at several levels.

The people most vulnerable to Listeria monocytogenes are as follows:

  • Elders.
  • Diabetes poorly controlled or with many years of evolution of the disease.
  • Pregnant.
  • Infants.
  • Patients with solid or Hematology, cancer by chemotherapy treatment that involves both the cancer itself.
  • People with AIDS.
  • Patients in chronic treatment with corticosteroids.
  • Sick of the liver or kidney.

All have in common a State of more or less consistent and more or less intense immunosuppression. In the Symptoms section, we explain the clinical impact in some countries for having particular characteristics.

What is listeriosis

Symptoms of listeriosis can be little specific, so infection sometimes is confused with other diseases. The incubation period of listeriosis, moreover, is long, and how it can affect various parts of the body the symptoms vary, although the disease usually occur with fever, severe pain, muscle pain, and nausea and vomiting. Below, we describe the symptoms, according to the characteristics of the patient and the area of the body affected by listeriosis.

Listeriosis in pregnant women

Infection by Listeria in a pregnant woman has a characteristic clinical picture or a considerable gravity for the pregnant woman. Tends to occur in the third quarter and appears as a disease mild with not very high fever, joint pains and muscle, and general malaise. He is often mistaken for a viral picture, and rarely is diagnosed.

The importance of Listeria infection in pregnancy is linked to the risk of infection to the fetus through the placenta. When this happens it can cause a miscarriage by fetal death prenatal, which in the last trimester of pregnancy is a very tragic situation for the pregnant woman and her family. In other cases, Listeria causes other diseases, that will manifest themselves in the baby after the birth.

Listeriosis in neonates

The picture in the newborn depends on the time where he has had contact with Listeria.

If the infection has happened when the baby was still inside the mother and days prior to delivery, often appears a picture of sepsis.

In more serious cases an infanto-septic granulomatosis is developed. This painting is characterized by abscess formation of Listeria in the innards of the baby. The abdomen is swollen and can take a bluish; Sometimes the internal organs, enlarged, even with dents by abscesses are palpable. It’s a situation very serious and very difficult to cure.


Sepsis is the disease that most commonly causes Listeria monocytogenes in immunocompromised patients. Often starts as a picture of more or less continuous, high fever, but without a source clear and no more symptoms. It is the passage of Listeria to the bloodstream. Little by little the patient worsens and alter their vital signs, and may result in septic shock with hypotension, tachycardia, and cold sweat, having a very high risk of death. Many patients with sepsis are at the same time a Listeria meningitis.

Infections of the nervous system

What is listeriosisIt is the second most frequent clinical picture produced by infection by Listeria. In fact, during the last years, cases in patients aged 60 years and immunocompromised have increased continuously. Outbreaks of infection due to consumption of contaminated food usually appear in this way or as a sepsis. Is also a relatively common in adolescent patients without immunosuppression detected.

The infection of the central nervous system translates into a meningitis that develops in a few days. The patient is complaining of headache, fever, and presents rigidity of nape (signs and classic symptoms of meningeal syndrome). However, in the types of patients who are affected by Listeria symptoms may be less accused and the diagnosis of meningitis can be suspected when it has already been several days of evolution. Other boxes that may cause this bacterium in the nervous system are the meningoencephalitis and intracranial abscesses, although they are less frequent.

Although these are the most typical clinical pictures of Listeria monocytogenes, is certain that much more rare infections can occur in almost any part of the body (endocarditis, gastroenteritis, pneumonia, etc).

What is listeriosis

A high suspicion by the physician is required to reach the diagnosis of listeriosis or infection by Listeria monocytogenes. As we have seen, nothing can make us think at first in a Listeria infection: there is a particular focus of transmission, and the signs and symptoms tend to be very non-specific. There is only one fact that must be placed when Listeria in a likely option: States of immunosuppression.

To be able to give a definitive diagnosis of listeriosis is needed to identify the causative organism in a sample that is usually sterile; same happens in virtually all infectious diseases. Pick up sample depends on the clinical picture.

In cases of sepsis and infanto-septic granulomatosis, a blood sample is taken and grown so bacteria grow and be able to identify it. The general blood test show high levels of white blood cells, but not in all cases, because that is precisely the deficit of cell-mediated immunity which prevents the infection. The levels of reactive inflammatory substances, such as PCR, Yes will be high.

In cases of meningitis to take sample will be cerebrospinal fluid by lumbar puncture. You can cultivate to detect the bacteria in the blood, but we also found other signs of infection, such as the presence of leukocytes directly (more frequent in blood), low levels of glucose, and the increase in total protein.

What is listeriosis

Treatment base of listeriosis in either case is the eradication of the bacteria from the body of the sick by antibiotic treatment. Antibiotics are drugs capable of destroying bacteria or prevent their replication. The first antibiotic discovered was penicillin by Alexander Fleming, at the beginning of the 20th century, and even today continues to be an effective and powerful drug.

Listeria monocytogenes is fought with a derivative of penicillin, ampicillin, which does not destroy the bacteria directly, but prevents its replication, and that is enough so they stop infection.

In the most serious cases, for example that occur in the infant, it is best to add another type of antibiotic, such as gentamicin. Gentamicin belongs to the Group of the aminoglycoside antibiotics that prevent the bacteria to produce more proteins, which leads her to death. Other antibiotics, can be used as e.g. co-trimoxazole and, in any case, it must begin with antibiotic treatment even without having confirmed safely infection by Listeria monocytogenes. A recent problem to fight this infection is the appearance of the common antibiotic-resistant strains of Listeria.

In addition to antibiotic treatment, other measures must be taken with the patient infected with Listeria. Some of them are control of fever with antipyretics, the tension control with cardiac drugs/steroids in cases of meningitis, sepsis cases oxygen, etc. It is important to begin treatment at an early stage, since survival to Listeria infection is linked to a rapid and effective intervention.

What is listeriosis

The prevention of the transmission of Listeria monocytogenes, which is very important to avoid that the baby is infected, especially in the case of pregnant women through control of the food that we consume. The measures to be taken to prevent Listeria infection are:

  • Persons who have a viral picture should not handle food in the industry or restaurants, or of course at home.
  • Always wash your good hands before handling food. Extreme hygiene in your kitchen and utensils you use to prepare food.
  • Read carefully and follow the instructions for the conservation of the packaged food.
  • Cooking food at high temperatures by any means (iron, cooking, microwave,…).
  • If you eat raw products (type sushi), do so only at sites that offer total guarantee of quality.
  • Save milk and derivatives in the refrigerator less than 5 ° C. Listeria can survive at low temperatures, so it should not drink unpasteurized milk.
  • Wash fruits and vegetables well before eating, especially the biologically cultivated.
  • If you are pregnant, check immediately to your doctor if you experience symptoms similar to a cold, headache, fever, muscle aches, nausea and vomiting.