What causes listeriosis?

Cause of listeriosis

The cause of human listeriosis is the species Listeria monocytogenes of the genus Listeria, which, according to the 9th edition of Bergey's guide, is classified as group 19 of microorganisms - gram-positive non-spore-forming rods of regular shape. Listeria are facultative anaerobes. They are acid-labile, unpretentious, do not form spores or capsules, and grow well on conventional nutrient media.

The antigenic structure of listeria is complex, there are 16 serological variants depending on the combination of somatic (15) and flagellar (4) antigens. Listeria ferment glucose. They are catalase-positive, oxidase-negative. They form cytochromes, are mobile at 20-25 °C; they can transform into L-forms and parasitize intracellularly, which causes insufficient effectiveness of antibacterial therapy in some cases, explains the tendency of listeriosis to a protracted and chronic course, the possibility of a latent form and bacterial carriage.

Pathogenicity factors - listeriolysin O, which has hemolytic activity and determines the virulence of the microbe; phosphatidylinositol; internalin A; internalin B; ActA protein, etc.

Listeria are highly resistant in the environment, grow in a wide range of temperatures (from 1 to 45 °C) and pH (from 4 to 10), and are capable of multiplying in soil, water, plants, and in the organs of corpses. In various food products (milk, butter, cheese, meat, etc.), they multiply at the temperature of a household refrigerator. At 70 °C, they die in 20-30 minutes, at 100 °C - in 3-5 minutes; they are inactivated by a solution of formalin (0.5-1%), chloramine (3-5%), and other common disinfectants. Listeria are sensitive to penicillins, tetracyclines, aminoglycosides, and 3rd generation fluoroquinolones.

Pathogenesis of listeriosis

Listeria enters the human body through the mucous membranes of the gastrointestinal tract, respiratory organs, eyes, genital tract, damaged skin, through the placenta of a pregnant woman to the fetus. An inflammatory process develops at the entry point, with regional lymph nodes often involved. Resident macrophages or monocytes absorb bacteria in the process of non-specific phagocytosis. Some of the listeria die, the remaining ones multiply intracellularly. With an adequate immune response of the body, further movement of listeria does not occur. Otherwise, microbes can spread from the entry gates by hematogenous and lymphogenous routes, penetrate the reticular-endothelial system (liver, spleen, lymph nodes), the central nervous system, kidneys, etc., where they further multiply with the formation of granulomas consisting of reticular, monocytic cells, cellular detritus, altered polymorphonuclear leukocytes; in the center of the granulomas, clusters of Listeria (gram-positive argyrophilic short rods, located in chains or in pairs) occur. The progression of the process causes necrotic changes in the center of the granulomas. Subsequently, the organization of necrotic foci, resorption of necrotic cellular elements with possible scarring occur. Specific granulomas can most often be found in the liver.

Listeria is capable of overcoming the blood-brain barrier and affecting the membranes and substance of the brain.

In congenital listeriosis, the granulomatous process is generalized and is treated as granulomatous sepsis. During external examination of a newborn with listeriosis, multiple white-gray granulomas 1-2 mm in diameter are detected, in some cases a rash on the skin, papular with a hemorrhagic rim or roseolous. During autopsy of those who died from listeriosis, all organs on the surface or in the section seem to be sprinkled with millet: white-gray, gray-yellow granulomas are found under the pleura, in the lungs, under the liver capsule and in its tissue, in the kidneys, under the pia mater, in the brain matter, spleen, lymph nodes, intestines, stomach, adrenal glands, thymus. Microscopically, productive vasculitis, foci of necrosis in the dermis with the formation of granulomas, and hyperemia are observed in the skin. In the liver, multiple submiliary foci of hepatocyte necrosis with pronounced hyperplasia and proliferation of stellate endotheliocytes are detected, in place of which the granulomas described above are formed.

The main role in the destruction and elimination of listeria from the body is given to cellular immune reactions, the leading role is played by cytotoxic suppressors, to a lesser extent - helpers. The significance of the humoral response is small, as in other infections with intracellular parasitism of the pathogen.

Epidemiology of listeriosis

Listeriosis is classified as a sapronosis, the main source and reservoir of the pathogen are environmental objects, primarily soil. Listeria are also isolated from plants, silage, dust, water bodies and wastewater. The source of listeria can also be various animals (rabbits, pigs, cows, dogs, cats, chickens, mice, rats, etc.).

The main route of infection of a person with listeriosis is food, when consuming various food products (meat, dairy, root vegetables) that have not undergone heat treatment, especially if they have been previously stored in the refrigerator for a long time. Soft cheeses, vacuum-packed sausages, as well as fast food products such as sausages ("hot dog", "corn dog"), hamburgers, etc. pose an increased danger.

It can also be transmitted by contact (from infected animals and rodents), airborne (in rooms where skins and wool are processed, as well as in hospitals), transmitted (from insect bites, in particular ticks), or sexually.

Of particular importance is the ability of listeria to be transmitted vertically from a pregnant woman to her fetus during pregnancy (transplacentally) or during childbirth (intranatally). Listeria can cause hospital-acquired infections, particularly in maternity hospitals. The source of the infectious agent in this case is women in labor with unrecognized listeriosis or their newborns. In the human population, asymptomatic carriage of listeria is 2-20%, and listeria is isolated from the feces of healthy people in 5-6% of cases.

Despite the fact that many food products are contaminated with listeria and a person is infected many times during his life, people get sick with listeriosis relatively rarely: it depends on both the virulence of listeria and the state of the human immune system. People with weakened immunity are most susceptible, especially pregnant women and newborns, as well as HIV-infected people, cancer patients, patients with diabetes, chronic alcoholism, etc. Due to the possibility of infection from animals, workers at livestock farms, meat processing plants, poultry farms, etc. are also at risk.

The currently observed and predicted future increase in the incidence of listeriosis is due to the high adaptive properties of listeria, their ability to reproduce in an abiotic environment, including in food products, an increase in the proportion of people with various immunodeficiencies in the human population, and the predominance of the food route of infection.

After listeriosis, long-term immunity is formed. Repeated cases of listeriosis have not been described.

The incidence is predominantly sporadic, less often group-based, and the mortality rate reaches 15-17%.

[ 1 ], [ 2 ], [ 3 ], [ 4 ], [ 5 ], [ 6 ]