Contents
Listeriosis is a bacterial infection caused by Gram-positive Listeria monocytogenes. The disease occurs mainly in people with immature or impaired cellular immunity. The risk groups include newborns, pregnant women, the elderly, patients after organ transplants, patients with neoplastic diseases, cirrhosis of the liver and people undergoing immunosuppressive treatment. Previously healthy people can also get sick.
The occurrence of listeriosis
L. monocytogenes is widespread in the natural environment. We can find it in soil, sewage, water, rotting plants, silage, in wild and farm animals, as well as in food products. Food contamination may include:
- raw vegetables and fruits,
- unpasteurized dairy products (milk, cheese, ice cream),
- raw, cooked and frozen poultry and meat
- raw and smoked fish.
Nowadays, the risk of infection is also associated with consumption of ready-to-eat delicatessen, semi-finished products and fast food products. About 5% of people are asymptomatic carriers of bacteria in the gastrointestinal tract. Carrier rates are greater in people with kidney transplant (may exceed 20%) or under immunosuppressive therapy, especially when treated with corticosteroids. Apart from the alimentary tract, infection can occur through the placenta, infected reproductive tract and cross-infections in neonatal wards. Direct contact with infected cow’s abortion material and infected poultry may cause limited skin infections in veterinarians.
Read more about bacterial food poisoning.
Despite the presence of L. monocytogenes in the human environment, the incidence of listeriosis is low and amounts to approx 0,7 cases per 100 people. The risk of developing the disease increases 3 times in people over 70, it is 17 times higher in pregnant women and as much as 100-200 times higher in patients with AIDS than in the general population. In recent years, 30-40 cases have been reported annually in Poland. This number significantly differs from the epidemiological data presented above, which may be the result of insufficient diagnosis or low reporting of cases treated in our country.
The causes of listeriosis
It causes listeriosis in humans infection with a strain of bacteria of the species Listeria monocytogenes. It is a gram positive, mobile, catalase positive, oxidase negative, non-enveloped, non-sporulating rod. On a medium with blood, listeria can produce beta hemolysis. Bacterial growth is possible over a wide temperature range: from 4 ° C to 37 ° C. Contrary to other bacteria, it grows in the temperature range found in refrigerators (from 4 ° C to 10 ° C), which is important both for epidemiology of diseases and can be used in microbiological diagnostics. The optimal temperature range for bacterial growth is from 30 ° C to 37 ° C, bacteria only move at 25 ° C. The sticks grow on ordinary substrates, however, selective substrates are used for their isolation from biological materials. On the basis of somatic O and ciliary H antigens, 13 serotypes are distinguished, Serotypes 1 / 2a, 1 / 2b and 4b are responsible for the majority of human infections. Serotype 1 causes the most cases in Poland.
The most common form of infection in immunocompromised people is listeriosisand then – inflammation of the meninges and the brain. In some patients, listeriosis occurs in the form of inflammation of the brainstem or brain abscesses, and endocarditis caused by L. monocytogenes is also possible.
We rarely observe other clinical forms:
- local infections – conjunctivitis,
- skin infections
- inflammation of the lymph nodes,
- inflammation of the lungs, joints, bone marrow and bones,
- pericarditis and myocarditis,
- inflammation of the eyeball
- gastrointestinal infections.
Find out about bacterial meningitis.
The mechanism of listeriosis formation
L. monocytogenes is an intracellular pathogen with a unique ability to infect and survive in macrophages and neutrophils as well as in non-phagocytic cells such as endothelial cells, hepatocytes and fibroblasts.
How is it infected?
Infection usually begins with eating food that has been contaminated with the stick. The incubation period is 11 to 70 days (on average about a month). Bacteria cross the intestinal mucosa barrier by active endocytosis through endothelial cells. Then comes the bacteremia phase, the bacteria reach many places in the body through the bloodstream – they are tropic to the cells of the central nervous system and the placenta.
Listeria bacteria have proteins called internalins that interact with E-cadhedrin, a receptor found on the surface of epithelial cells and hepatocytes. This reaction initiates bacterial phagocytosis. Low pH in the phagolysosome environment of the host cell stimulates the activation of a specific L. monocytogenes haemolysin – listeriolysin O. It causes the formation of pores in the phagosome membrane, thanks to which bacteria enter the cytoplasm and are not destroyed by lysosomal enzymes. Bacteria rapidly multiply in the cytoplasm, and in the defense mechanism, bacteria are surrounded by actin filaments. Another bacterial cell surface protein – ActA – influences the actin polarization in such a way that it enables the movement of bacteria inside the cytoplasm of the host cell. After reaching the cell membrane, the bacterium forms a kind of spike in it, which can be absorbed by adjacent cells (macrophages, enterocytes and hepatocytes). Thus, infection with L. monocytogenes can spread to subsequent cells, avoiding contact with antibodies, complement components or neutrophils.
Listeriosis and anatomopathological changes
In neonatal listeriosis, numerous granulomas (granulomatosis infantisepticum) are present in the internal organs. Macroscopically, they look like tiny gray-yellow nodules. Microscopically, the infiltration consists of lymphocytes, monocytes, plasma cells and neutrophils. Diffuse infiltrates of microglia, leukocytes and macrophages occur in the brain tissues. In turn, there are numerous bacteria in the lumen of small vessels.
The microscopic image of materials collected from the organs of patients with listeriosis and listeriosis meningitis does not differ morphologically from the image seen in the course of these diseases caused by other bacteria.
Source: J. Cianciara, J. Juszczyk, Infectious and parasitic diseases; Czelej Publishing House