Listeria

Listeria is a variety of microorganisms, which are represented by 6 types of gram-positive rod-like bacteria. The microorganism is named after the famous English surgeon, the founder of aseptic and antiseptic methods in medicine, Joseph Lister.

Listeria is quite common on the planet: it is especially known in veterinary medicine, as it often affects domestic animals. But in some cases, the microorganism can be dangerous to humans.

[1], [2], [3], [4]

Listeria Bacteria

Listeria bacteria are gram-positive, non-controversial, rod-shaped microorganisms. Among the 6 common species of these organisms, Listeria monocytogenes is especially important for medicine, as it can provoke the development of the disease, both in animals and in humans. Other species of listeria bacteria, for example, Listeria ivanovii, affect only wild and domestic animals, and Listeria innocua, Listeria seeligeri, Listeria grayi and Listeria welshimeri are generally recognized as harmless microorganisms.

A few reports on the lesions of these microorganisms of people most experts attribute to the fact that in our country there are not so many laboratories in which they can determine listeria and antibodies to it. According to statistics, the number of lesions in human listeria is relatively small, but the number of deaths in patients with listeriosis is above average, and in infants - up to 75%.

Especially dangerous is infection during pregnancy, as it can provoke difficulties with bearing a child, the birth of dead children, early childbirth and the early death of newborns. In addition to women and infants, listeria often causes disease in the elderly and the elderly, who are ill with septic and meningoencephalic forms of listeriosis. First of all, people get sick weakened, with poor immune protection, with concomitant oncology or autoimmune pathologies. Over the past few years, the number of cases of listeriosis in people who take drugs has increased.

Listeria monocytogenes

Listeria monocytogenes - the causative agent of listeriosis - is a small mobile rod that does not form a spore and is beautifully colored by the Gram method (Gram +). These organisms belong to the Corynebacteria, the most famous representative of which is the diphtheria wand. For this reason, microbiologists often characterize this microorganism as a species similar to diphtheria, and only after thorough analysis isolate the belonging of the microorganism to the bacteria of listeria.

This organism has the form of a short straight rod with a size of approximately 0.4-0.5 by 0.5-2 μm, with smoothed tips. Microorganisms can be located on one, or small links of 4-5 bacteria, extremely rarely - long chains. They are not capsular forming.

When placed on a nutrient medium, this myco-organism grows in the form of small (up to 2 mm), smooth-convex, oblong colonies, a gray-blue or greenish shade, half transparent. If the microorganisms are cultivated on a liquid medium, then an even turbidity is detected with the subsequent appearance of a precipitate. If the culture medium is semiliquid, the colonies grow more on the surface. The grown material has a curd or whey odor, which indicates the accumulation of residual carbohydrate metabolism in the culture medium.

Listeria structure

Listeria bacteria are mobile, they can have from 1 to 4 flagella, due to which they move and perform peculiar "somersaults". The greatest activity is at 20-25 ° C, and growing at 37 ° C sharply reduces their mobility, until complete fading.

Bactreia listeria belong to facultative aerobes (that is, their presence requires the presence of oxygen), germinate well in glucose-serum media.

Organisms are very stable in the external environment, can grow successfully in a wide temperature range (from + 1 ° C to + 45 ° C) and ph-medium (4-10). Listeria bacteria do not feel bad at low temperatures, they can multiply already at t ° + 4-6 ° C in the ground, in water bodies, on the surface of plants, in cadaver meat, in food.

The life cycle of a listeria bacterium without problems also occurs in a refrigerator: microorganisms are able not only to preserve their vital activity, but also actively multiply and accumulate on products, while other microorganisms inhibit and stop their development. For this reason, placing contaminated food in the refrigerator does not protect the person from infection. The same applies to listeria bacteria and salting of the products: bacteria are able to withstand up to 20% of the salt solution.

However, the bakreis of listeria die fast enough at boiling, although during pasteurization (at t ° + 60-70 °) they perish only within half an hour. But even high temperatures of listeria can endure if they are located in the middle of cellular and tissue structures. For example, there are cases of development of listeriosis after the use of pasteurized dairy products: the bacteria did not die, being in single leukocyte and epithelial cells, which were subsequently found in the sediment.

In the open air, the bacterium listeria perishes when treated with disinfectants (chloramine, formalin), and also under the action of ultraviolet rays.

In the external environment, the listeria bacterium retains its ability to live and develop for 90-120 days, in the soil - up to 600 days, on products - up to 30-90 days.

Listeria and listeriosis

Most often a person can become infected with a listeria bacterium during contact with a sick domestic animal, or after consuming food poisoned by bacteria: meat, milk, fish, vegetables, etc. Soft varieties of cheese, meat products, salads are especially susceptible to infection. Meat products can contain Listeria bacteria in 35-45% of cases.

A person has a high risk of developing listeriosis if his professional activities are related to birds, animals or their products. This especially applies to workers of meat and poultry plants, farms, milk processing enterprises and fish farms.

Listeria bacteria in meat (chilled) somewhat inhibit their vital activity, but complete death of bacteria does not occur. If the meat was frozen at a temperature of -10-28 ° C, even under such conditions, the pathogen is detected after 1 year or more, and at the same time it is absolutely viable. When processing meat and by-products with sodium chloride, listeria remain viable for 2 months or more. When heat treatment of sausages, the causative agent of listeriosis can die only after one and a half to two hours. All of the above facts make it possible to verify that if the animal is suspected of being listeriosis, its meat can not be eaten in food categorically.

Listeria bacteria are found in fish no less often than in meat. The diverse mycorrhizons that are present in fish products along with the listeria bacterium, in some way inhibit their reproduction. For this reason, the number of listeria bacteria in the cooled fish product may be uncritical (up to 100 bacteria per gram). But those conditions that are created when salting and cold smoking method, inhibit the development of other microorganisms, but the listeria at this time begin to multiply actively. This explains the presence of more Listeria bacteria in cold-smoked fish products, salted fish and preserves.

The causative agent of listeriosis can get to the fish processing enterprises with caught fish (especially freshwater), with vegetable additives, dirty water, with packing containers.

At particular risk are workers who perform the initial stage of processing fish (scaling, cutting).

And, despite the fact that the ingestion of the bacterium listeria into the human body with food is considered the most common, it should be remembered that listeria can penetrate in other ways - through the respiratory system, the eye conjunctiva and through scratches and wounds on the skin. A sick person, or carrier of parasites, secretes bacteria with feces, urine. Especially dangerous are the carriers of the infection, who do not know about their disease, while infecting others. Infection can occur in utero, as well as with labor.

GOST Listeria

The method of detection and detection of Listeria bacteria in food products is designated as GOST R 51921-2002. This common technique applies to all foods, including children's, medical and special foods: meat products (also poultry), internal organs and less valuable parts of carcasses, fish products, dairy products, vegetables, margarine, mayonnaise, ready-made salads. GOST defines the detection technique in the listed products of the bacterium listeria monocytogenes.

The method is based on sowing some part of the tested product in a liquid selective nutrient medium, with further re-entry to diagnostic-selective media and sprouting crops when creating optimal conditions.

The difference in cultivated crops is carried out step by step: first they ascertain the belonging of the grown bacteria to the genus Listeria, and then proceed to confirm their belonging to the species Listeria monocytogenes.

Antibodies to Listeria

Antibodies to listeria bacteria are an indicator of infection with these microorganisms, which cause the development of listeriosis. Determination of antibodies to Listeria is carried out in the following situations:

• with suspected listeriosis;
• with severe intoxication, high temperature, rash, liver and spleen enlargement;
• when diagnosing an unexplained infection.

Also, the analysis is necessarily prescribed for women who previously had this disease, when planning pregnancy.

Preparation for analysis is not required. A health worker takes blood from a vein for examination.

In the norm of antibodies to bacteria, listeria should not be. In other situations, the analysis may show the following results:

• 1:50 - doubtful titration;
• 1: 100 - the titre is weakly positive;
• 1: 200 to 1: 400 - positive;
• 1: 800 and above - the titre is sharply positive.

A positive result indicates the presence of a current infection in the body.

[5], [6], [7], [8]

Selective additive for highlighting listeria

A selective additive for the isolation of listeria can be used for bacteriological diagnosis of listeriosis or for the detection of listeria bacteria on environmental objects.

Listeriosis is quite widespread in the world, but in our country, fortunately, the percentage of detection of patients and carriers of Listeria bacteria is relatively low. Nevertheless, the use of selective media is an important point of sanitary and hygienic requirements and bacteriological control of products.

Selective additives can be purchased separately, or as part of a ready-made medium for isolation and cultivation of listeria bacteria. Most often, the additive is released in the form of a powder, which is subsequently added to the broth or other media, where optimal prerequisites for the cultivation of listeria will be created. In addition, inhibitory substances that inhibit the simultaneous growth of another bacterial flora present are added to the medium.

The examination of the material is carried out according to GOST for determination of Listeria monocytogenes. It is incubated at t ° + 30 ° C during the day.

Shelf life of selective additives - about 2 years.

Listeria, when ingested, spreads quite quickly, affecting those parts of the body and the central nervous system where medicines can not enter the required volume. For this reason, treatment of listeriosis is not always effective, especially if the diagnosis is carried out quite late. In this regard, early detection of listeria bacteria is the most important moment in the successful treatment of the disease.