What Is Listeria?

Listeria monocytogenes (Listeria monocytogenes), also listed Listeria monocytogenes, Listeria monocytogenes, is a facultative anaerobic bacteria, is the pathogen of Listeria. Listeria is a Gram-positive bacterium that belongs to the thick walled phylum, named after Joseph Lister. It is mainly borne by food and is one of the most deadly foodborne pathogens ^[1] .

Listeria is ubiquitous in the environment and can be found in most foods. Meat, eggs, poultry, seafood, dairy products, vegetables, etc. have all been proven sources of Listeria infection. Listeria poisoning can cause blood and brain tissue infections. Many countries have taken measures to control listeria in foods and formulated corresponding standards.

Chinese scientific name: Listeria
boundary: Bacterial kingdom
door: Pachyphyte

Tsuna: Bacillus
Head: Bacillus
Genus: Listeria
distribution area: all around the world

Listeria monocytogenes

There are ten strains of Listeria monocytogenes recognized internationally:

1. L. monocytogenes

2. Listeria monocytogenes (L.iuanuii)

3 L.innocua

4 L.welshimeri

5. Listeria monocytogenes (L. seeligeri)

6. L.grayi

7. L.murrayi (Suspected, WHO and The Prokaryotes (

(Rosenberg, Eugene & DeLong, Edward F.) Among the 10 species, there are L. marthii and no L. murrayi)

8. L. rocourtiae

9. L. fleischmannii

10. L. weihenstephanensis

Among them, according to the 16S rRNA sequence, L. grayi has been isolated from genus Listeria and belongs to genus murraya.

Among them, Listeria monocytogenes is the only one that can cause human diseases. Listeria monocytogenes is a common soil bacterium. In the soil, it is a saprophytic fungus that feeds on dead and decaying organic matter. It is also a contaminant in certain foods, mainly fresh milk products, and can cause severe food poisoning. Listeria monocytogenes is a zoonotic pathogen. It can cause listeriosis in humans and animals, and is mainly manifested as sepsis, meningitis, and mononuclear cells after infection. It exists extensively in nature. The presence of Listeria monocytogenes in food is dangerous to human safety. The bacteria can still grow and reproduce in a 4 ° C environment. It is one of the main pathogens that threaten human health in refrigerated foods. A new study on the Listeria monocytogenes transcriptome (the entire mRNA transcript in a cell) under a range of different growth conditions sheds light on the nature of this transition from saprophytic to a pathogenic lifestyle. The data from this study showed an unexpectedly complex transcription program involving 50 non-coding RNAs, as well as a series of new regulatory RNAs, including several long antisense RNAs. During the infection process, Listeria successfully reshapes its transcriptional program through coordinated set of transcriptional changes, in which certain non-coding RNAs are preferentially expressed in cells growing in the small intestine or blood.

Listeria characteristics

1. Widely distributed: exist in soil, waters (surface water, sewage, wastewater), insects, plants, vegetables, fish, birds, wild animals, poultry.

2. The living environment is highly plastic: it can survive at 2-42 ° C (it is also reported that 0 ° C can grow slowly) and can grow and reproduce in a refrigerator for a long time.

3 Large range of adaptation: Adaptable under both acidic and alkaline conditions.

4 Foods with higher bacteria include: milk and dairy products; meat (especially beef); vegetables; salads; seafood; ice cream and so on.

Listeria is widely distributed in nature and can be found in rotten plants, soil, animal waste, sewage, silage and water. In general, Listeria may be found in places where lactic acid bacteria, filamentous bacteria, and some coryneform bacteria live. Their relationship with dairy products and silage is as well known as the relationship between lactic acid bacteria and these products. A study of seagull manure, rooks and silage in Scotland found that seagulls foraging on sewage treatment sites carry more Listeria than other places. Rook manure samples often contain A small amount of Listeria. Listeria monocytogenes and listeria monocytogenes are frequently found, whereas listeria monocytogenes is found in only one sample. In this study, Listeria monocytogenes and Listeria monocytogenes were found in 44% of moldy silage and 22.2% of large bales. In Denmark, 15% of the 75 silage samples were positive for Listeria monocytogenes, and 52% of the stool samples of 75 cows contained the bacteria. Listeria monocytogenes was found in silages with pH values above and below 4.5. It was isolated from 8.4% to 44% of samples from corn fields, pastures, silt, animal manure, wild animal farms and other related sources. Listeria monocytogenes has been shown to survive 295 days or more in moist soil. In a study of California coastal waters, 62% of 37 fresh or low-salt samples were positive for 17.4% of 46 silt samples, and Listeria monocytogenes was not cultured in 35 oyster samples ^[1] .

Listeria monocytogenes

At the end of 1999, the worst food poisoning incident in history in the United States caused by the consumption of foods containing Listeria monocytogenes. According to data from the Centers for Disease Control and Prevention, 14 people in Michigan, the United States, were contaminated by the bacteria due to consumption. "Hot dogs" and cooked meat died in 97 people in 22 other states and 6 women miscarried.

Listeria monocytogenes was found in cheese and pork produced in France from 1992 to 1995. Since November 2001, China's quality inspection department has repeatedly imported from more than 20 meat processing plants in the United States, Canada, France, Ireland, Belgium, and Denmark. Pathogenic bacteria such as Listeria monocytogenes and Salmonella were detected in more than 30 batches of nearly 1,000 tons of pig by-products, including pork loin, pork belly, pig ears, and small steaks.

The U.S. Centers for Disease Control and Prevention said on September 28, 2011 that 72 people in 18 states of the United States had contracted the disease due to eating melon contaminated with Listeria monocytogenes. The U.S. Journal of the United States reported that Listeria monocytogenes had killed 16 people in the United States. This is the largest food-borne disease outbreak in the United States since 1998. Listeria monocytogenes has a long incubation period, usually from 1 to 8 weeks from the consumption of contaminated food to the onset of disease. Therefore, the CDC estimates that as more symptoms of Listeria infections begin in October, the number of confirmed cases will continue to increase.

Listeria is more deadly than common salmonella and some E. coli. The last large-scale outbreak of Listeria infection in the United States occurred in 1998, when 21 people died of eating cooked meat such as hot dogs infected with the disease. In 1985, 52 people died from eating soft cheese infected by the bacterium.

After investigation, Jensen Farm in Colorado was the source of the large-scale Listeria infection. The farm announced the recall of "Rocky Ford" brand melon from September 14. However, it is unclear how Listeria contaminates this fruit. The US Food and Drug Administration director Margaret Hanberg said this is the first time Listeria has been found inside a complete melon, and the agency is working to find out why. Jensen Farms said they sold the brand of cantaloupe to 25 U.S. states, but the Food and Drug Administration believes the area may be wider because the outbreak has exceeded the farm's sales list. Jensen Farms said they sold more than 300,000 boxes of problem cantaloupe, 5 to 15 boxes per box, so the total recall of cantaloupe was between 1.5 and 4.5 million.

The director of the Centers for Disease Control and Prevention, Frieden, said that although the contaminated muskmelon has been removed from the shelves, the germ may still be "disorderly" because it has strong vitality and can survive in low temperature environments and even refrigerators.

Listeria usually spreads and grows on expired instant foods, butter, frozen meat and cheese. The Food and Drug Administration says that there are about 800 cases of Listeria infection in the United States each year, and most of the food is not the culprit of human infection because of the food. People with poor immunity, such as the elderly, pregnant women and patients with chronic diseases, are most likely to be infected with Listeria. The CDC said that the 13 dead were mostly elderly, with an average age of 78 years.

It is reported that once infected with Listeria monocytogenes, symptoms such as fever, muscle pain, nausea, and diarrhea appear, while symptoms such as headache, stiff neck, physical imbalance, and cramps occur. Infected pregnant women may experience premature, miscarriage, and stillbirths, and infant health may also be affected. ^[3]

Listeria epidemiology

Listeria monocytogenes is widely found in nature, it is not easy to be thawed and can withstand high osmotic pressure. It is found in soil, surface water, sewage, waste water, plants, silage, and rotten vegetables. Therefore, animals can easily ingest the bacteria and spread them through the oral-fecal route. According to reports, the carry rate of Listeria monocytogenes in feces of healthy people is 0.6-16%, 70% of people can carry bacteria for a short time, 4-8% aquatic products, 5-10% milk and its products, 30% The above meat products and more than 15% of poultry were contaminated with the bacteria. People eat soft cheese, underheated chicken, unheated hot dogs, fresh milk, pasteurized milk, ice cream

Listeria colonies Ling, raw steak, lamb chops, cabbage salad, celery, tomatoes, French pies, frozen pork tongue, etc. are infected. About 85-90% of the cases are caused by contaminated food.

The bacteria can enter the body through the eyes and damaged skin and mucous membranes and cause infections. Pregnant women infect the fetus or newborn through the placenta or birth canal. The bacteria that inhabit the vagina and cervix also cause infections. Sexual contact is also possible for the disease to spread. Approach, and there is an upward trend.

Seasonal characteristics: It can occur in spring, and the incidence increases seasonally in summer and autumn.

Food types: The main foods are milk and dairy products, meat products, aquatic products, vegetables and fruits.

The sources of contamination and poisoning of Listeria in food:

The contamination of Listeria monocytogenes in milk mainly comes from feces; since carcasses are easily contaminated during the slaughter process, the hands of food professionals can also cause contamination during the sales process. Because the bacteria can grow and reproduce under refrigerated conditions, employing a refrigerator to refrigerate food cannot inhibit its reproduction. The severity of this bacteria is mainly caused by the invasion of a large number of Listeria monocytogenes; it is also related to Listeria hemolysin O ^[1] .

Listeria pathogenicity

Whether Listeria monocytogenes enters the body or not is related to the amount of bacteria and the age and immune status of the host, because the bacteria is an intracellular parasite, and the host s elimination of it mainly depends on the cellular immune function. , Pregnant women, adults over 40 years of age, and immunocompromised persons.

Listeria incubation period

Symptoms occur from 3-70 days after infection, and healthy adults may have mild flu-like symptoms, and those who are susceptible have sudden fever, severe headache, nausea, vomiting, diarrhea, sepsis, meningitis, and abortion in pregnant women.

The antigenic structure of Listeria monocytogenes has nothing to do with its virulence. Its pathogenicity and virulence mechanism are as follows:

1. Parasite-mediated intracellular proliferation allows it to attach and enter intestinal cells and macrophages.

2. For anti-activated macrophages, Listeria monocytogenes has a bacterial peroxidase dismutase, which makes it resistant to the decomposition of peroxidants in the activated macrophages, which are sterilizing toxic free groups.

3 Hemolysin, Listeria hemolysin O, can be obtained from the culture supernatant, is SH-activated cytolysin, there are two kinds of and , and it is a virulence factor.

Listeria clinical manifestations

Healthy adults have mild flu-like symptoms, and newborns, pregnant women, and immunocompromised patients show shortness of breath, vomiting, bleeding rash, purulent conjunctivitis, fever, convulsions, coma, spontaneous abortion, meningitis, and sepsis until death.

Listeria control

Listeria monocytogenes can survive general thermal processing. Heat treatment has killed the competitive bacterial population, making Listeria monocytogenes easy to survive under non-competitive environmental conditions. Therefore, in food processing, the core temperature Must reach 70 ° C for more than 2 minutes. Listeria monocytogenes is widespread in nature, so even if the product has been overheated and processed to fully inactivate Listeria monocytogenes, it may cause secondary pollution of the product, so it is extremely important to prevent secondary pollution after cooking. of. Because Listeria monocytogenes can still grow and reproduce at 4 ° C, unheated refrigerator foods increase the risk of food poisoning. Refrigerator food needs to be heated before consumption. If it is seafood such as sashimi, professional hotels will store it in a large freezer at about -40 degrees Celsius to ensure the killing of parasites and prevent bacterial infection.

Listeria related events

On October 7, 2019, the German Federal Consumer Protection and Food Safety Agency announced the recall of more than a thousand meat products. The reason is that it may be contaminated with Listeria. Its website publishes a catalog of more than a thousand recalled products, including sausages, pizza and bread. Many large supermarket chains in Germany have taken down related products. ^[2]