Listeria monocytogenes

Listeria monocytogenes is a Bactérie with Gram-positive, kind Listeria, division of the Firmicutes, which owes its name with Joseph Lister.

It is the only species of the pathogenic kind Listeria for the man; it is about a bacillus of small size, not sporulé, anaerobic optional, ubiquitaire (ground, plants, water…) Gram-plus, catalase+, mobile with 20 °C.

It is mobile thanks to its Flagelle S. According to certain studies, 1 to 10% of human would be healthy carriers of L. monocytogenes in their intestine.

Bacteriological characters

Morphology

Small squat bacilli, 1 to 2 microns out of 0,5 micron, regularly coloured, resembling bacilli pseudodiphteric with which it is necessary to avoid confusing them. They are characterized some by their mobility but this one is not obvious that in the cultures made between 20 and 30°C. In the colonies R, one can observe long filamentous forms.

Culture

aerobic - optional anaerobe,
transparent colonies from 1 to 2 mm,
on gélose with blood: small zone of hémolyse beta,
catalase +, H2S -,
develops until -2°C
pushes in the presence of Nalidixine: selective medium.

Antigens

Four types serologic have summers dédrits; types 1 and 4 are most frequent.

Experimental pathogenic capacity

The deposit of a drop of culture on the conjunctive one of a guinea-pig or a rabbit causes a keratoconjunctivitis purrulente (sign of Anton).

Sensitivity

However she does not survive more than 30 min +60 °C. Pasteurization eliminates it from food. At the temperatures of refrigeration, it continues to develop contrary to the majority of the other bacteria, which is selection criteria. She resists several months in the ground. She is destroyed with a pH lower than 4. This psychrophilous germ is sensitive to the majority of disinfecting: the Aldehyde S, derivatives chlorinated, iodized and quaternary ammoniums under the usual conditions of employment. It resists of as much better than the temperature is low and porous surface.

Habitat

One identified L. monocytogenes in at least 37 species of mammals, domesticated or not, and in at least 17 species of Oiseau X and probably in certain species of Poisson S and Coquillage S. One can isolate L. monocytogenes from the ground, and other sources of our environment. L. monocytogenes is rather resistant; it resists inter alia freezing (it is psychrophilous). L. monocytogenes has a pathogenic capacity.

The problem arising from Listeria monocytogenes in cooled food is its capacity to be developed with temperatures bordering 0°C. Even if the bacterial population is weak at the beginning, it is likely to increase during storage and of the distribution and to reach significant levels being able to cause the food listeriosis. It cannot develop in frozen food, but if the contamination takes place before deep freezing, the organization can survive and start again it to develop at the time of defrosting, reaching dangerous levels for the human health. The bacterium can be lodged in the digestive tract of certain mammals, including that of the man, which then prove to be healthy carriers of the bacterium.

Pathogenicity

The Infection by L. monocytogenes causes a disease, the Listériose.

Epidemiology

Incubation can last 2 to 70 days after the ingestion of food, which gene the retrospective search of food blamed at the time of a clinical episode. The infections can be grouped in time and one speaks then about epidemic of listeriosis. Isolated infections are also possible. In the case of the epidemics of listeriosis, the surveillance device installed in France makes it possible to identify food blamed. In France, the last epidemics were due to industrial pork-butcheries (rillettes and language of pig into cold) and soft cheeses. The prevention of the epidemics passes by a monitoring of food likely to transmit Listeria monocytogenes and periodically decisions of withdrawal of consumption are made. This monitoring minimizes the epidemic risk. Generally, the most capable food to transmit the listeriosis is those containing believed milk (milk, butter, soft cheeses), the smoked fish, the germinated seeds, the cooked pork-butcheries consumed without reheating, the believed pork-butchery, the believed shells and the close products (tarama,…). " The listeriosis is a rare disease, whose frequency was decreased by three since 1987; one passed from 661 cases then listed to 458 in 1992 and 228 in 1997 " , explains Anne-Marie Vanelle, sub-manageress of the food hygiene to the Head office of Food (DGAL). " This regular reduction is due to the efforts of the professionals, under the aegis of the monitoring services, in particular thanks to the recourse generalized to methods HACCP (Analysis of the risks and control of the critical points), for the control of the Listeria risk. The industrialists made gigantic efforts, but risk zero does not exist. Today, we arrived at a threshold where the efforts with respect to the raw materials must be accompanied by adapted information, in particular medical, which will make it possible cause a drop in the number of cases. " The speed of the placement of the preventive measure deserves to be underlined. The awakening is indeed recent: the assumption of a food transmission of the disease was confirmed only in 1981. Then the development of the analytical techniques made it possible to highlight the presence of Listeria in the majority of the intended products human consumption. Since, the regulation was packed and hardened, reinforced sanitary controls, the techniques of improved analyzes.

Mode of transmission

factors of transmission

External medium: ground, water, plants (ensilage), Animal products: milk, eggs, derivative products like cheeses with believed milk, meats, pork-butcheries, fish, dishes cold… Healthy carriers, chronicles and patients, Virulent matters represented primarily by the placenta, the urines and feces, the liquid cérébro-spinal, The chronic carriers or convalescents (for example, women having presented an abortion listérien) still excrete the bacterium during several weeks, Many arthropods (like the ticks and the flies), which are carrying Listeria and could thus play the part of vector. Listeria monocytogenes can exist in a natural state in food but generally it is brought there by contacts with contaminated products or surfaces of handling, preparation or by the instruments and machines being used for the preparation. In agribusiness industry, precautions are taken to eliminate Listeria monocytogenes from surfaces and machines used; frequent maintenance and disinfection are necessary and must be planned.

Modes of transmission

There exist three possible modes of transmission of the disease: Direct: primarily by hematogen way (congenital listeriosis). At the man, the transmission of the mother to the fetus can be done by see digestive or by respiratory tract (amniotic infection, aspiration of germs located in the collar or the vagina). A transmission by contact is possible (contamination of a farmer during a vélage). However, the cutaneous listeriosis is rare. The infections nosocomiales, i.e. transmissible infections at the time of therapeutic acts. Indirect: via an inanimate vector like the animal products: it is then about a contamination by digestive tract at the origin of the sporadic or epidemic cases at the man (epidemic of 1992 in France). A transmission by respiratory tract is possible, but it is rare; indeed, it is possible that the peasants working in the sheep-folds where the atmosphere is confined and where a regular cleaning is not carried out can contract the listeriosis. Note: the contamination by ticks carrying Listeria is possible, but rare.

Tracking

The infection is identified in blood, the céphalo-rachidian liquid or other taking away by the laboratories of bacteriology. The laboratory can then give indications useful for the therapeutic one. Serology is of a limited employment. Methods of molecular typing very precise and always applicable are used. Typing is carried out on proteins and the DNA. Typing by proteins is carried out by electrophoresis of isoenzyme (Multilocus enzymes analysis) which measures the electrophoretic variation of mobility of enzymes (ADH, G6PDH, fumarase…) This method makes it possible to identify 2 groups of Listeria monocytogenes: the first with stocks 1/2 B and 4 B, and the second with the stocks 1/2a and 1/2c. Typing by the DNA uses methods of traditional electrophoresis after the action of enzyme of restriction (Eco IH). Note: In front of any demonstration of febrility in the expectant mother, it is necessary to ask a hémoculture and to begin a antibiothérapie.

Treatment

There does not exist vaccination. This one was tried in the animals without satisfactory results. The use of vaccines alive or attenuated with nonvirulent stocks (nonhemolytic mutants) is disappointing. These mutants do not produce protective antibodies. The sensitivity of Listeria for antibiotics has evolved/moved little for several decades. The ampicilline and the amoxicilline always keep their place and their association with the aminosides is strongly bactericidal. The tétracyclines are active and the quinolones were used successfully like association sulphamide-triméthoprime. To stop the listeriosis, the doctors use especially pools of antibiotics, and in particular penicillin, the streptomycine and the sulphamides. This treatment is prolonged with lactamines. But the results remain random and depend especially on the state of the immune system of the patient. The therapy is effective if she is undertaken early. The treatment is necessarily of a few weeks in the case of listeriosis.

People at the risk

Listeria monocytogenes is an opportunist pathogenic bacterium, preferentially tackling the subjects whose immune system is disturbed. It is the case for: ~ elderly ~ expectant mothers. Thus, 1,6% of the terminatioies of pregnancy would be due to a listeriosis. ~ new-born babies. The listeriosis is the third infection néonatale after the infections with Escherichia coli and Streptococcus. ~ immuno-depressed people: cancer patients, persons receiving a transplant, sidéens, diabetics and dependant people with opiates and the tobacco. It is estimated that the sidéens contract listeriosis 300 to 600 times more quickly than the other people. There exist three groups in this case with a level of decreasing risk: People reached of hémopathies, transplanted, reached AIDS People reached of solid cancers, hépathopathies and the hemodialyses People diabetics badly balanced and alcoholic. Note: the quite bearing old subjects do not have a risk much higher than that of the general population and the children, same young, have an identical risk, even weaker, than that of the general population.

Prevention

Precautions to be taken for the prevention of the listeriosis in the immuno-depressed expectant mothers, patients and the elderly: To avoid the consumption of soft cheeses with believed milk To remove the cheese crusts before consumption To avoid the already grated sold cheese consumption To avoid the smoked fish consumption To avoid the raw germinated seed consumption (soya, alfalfa,…) Listeria monocytogenes can also contaminate products which undergo a cooking during their manufacture or storage. These products present the same risk thus as the contaminated believed products. According to the investigations, they are essentially prepared meat products: to avoid the rillettes, pies, foie gras, produced into cold… For these products, as well as the other prepared meat products (standard ham), to prefer the products prepackaged with the products with the cut and to quickly consume them after the purchase. Indeed, do not forget that there is only one score of manufacturers for several hundreds of marks. This means that contaminated chain will produce identical contaminated food, that it is under marks with the luxurious image or products without marks. Only the identification number of the manufacturer (whom one never reads on packing) will make it possible to identify the product. To avoid the consumption of products prepared meat raw consumed in the state like the plugs, the bacon, believed ham,… To make cook before consumption. These measurements are sufficient to eliminate the germs which are in majority on the surface of this food. Indeed, there is no Listeria in a cassoulet, a stew or a blanquette if these dishes are cooked at the house lengthily starting from fresh produce used quickly without storage. On the other hand, for the ground beef, which is reconstituted food and for which this concept of contamination on the surface cannot be retained, a cooking in heart is imperative. To separately preserve believed food (meat, vegetables, etc) of food cooked or ready to be consumed; after the not cooked food handling, to wash the hands and to clean the kitchen utensils which were in contact with this food. To avoid the consumption of products bought with the ray delicatessen To avoid the consumption of believed shells, surimi, tarama It is necessary to carefully wash believed vegetables and aromatic herbs The usual rules of hygiene must also be respected: The food remainders and the cooked dishes must be heated carefully before immediate consumption It is necessary to frequently clean and disinfect its refrigerator with chlorinated water

L off. monocytogenes is unknown goal probably vary with the strain and with the susceptibility off the victim. From boxes contracted through raw gold supposedly pasteurized milk, one may safely assumes that in likely persons, fewer than 1,000 total organisms may causes disease. L. monocytogenes may invade the gastrointestinal epithelium. Ounce the bacterium enters the host' S monocytes, macrophages, gold polymorphonuclear leukocytes, it becomes blood-limits (septicemic) and edge grow. Its intracellularly presence in phagocytic concealments also permits access to the brain and probably transplacental migration to the straws in pregnant women. The pathogenesis off L. monocytogenes centers one its ability to survives and multiply in phagocytic host concealments.

L. monocytogenes has been associated with such foods ace raw Milk, supposedly pasteurized fluid milk, Cheese S (particularly software-ripened varieties), Ice cream, raw Vegetables, fermented raw-meatus Sausage S, raw and cooked Poultry, raw meatuses (off all standard), and raw and smoked Fish. Its ability to grow At temperatures ace low ace 3°C permits multiplication in refrigerated foods.

When listeric meningitis occurs, the overall Mortality may reach 70%; from septicemia 50%, from perinatal/neonatal infections greater than 80%. In infections during pregnancy, the mother usually survive. Carryforwards off successful treatment with parenteral Penicillin gold Ampicillin exist. Trimethoprim-sulfamethoxazole has been shown effective in patients allergic to penicillin.

The methods for analysis off food are complex and time-consuming. Present The FDA method, revised in September, 1990, requires 24 and 48 hours off enrichment, followed by has variety off other tests. Total time to identification takes from 5 to 7 days, goal the announcement off specific nonradiolabled DNA honest should soon allow has off simpler and faster confirmation suspect isolates.

Recombining DNA technology may even 2-to-3 day positive analysis in the allowed future. Currently, the FDA is collaborating in adapting its methodology to quantitate very low numbers off the organisms in foods. -->

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