Listeria monocytogenes

2021-08-18 09:54 PM

Listeria monocytogenes causes disease in many animals, can be transmitted to humans, mainly in infants but also in adults

Listeria monocytogenes cause disease in animals and can be transmitted to humans.

Biological characteristics

These are Gram-positive, non-shelled, non-spore-forming bacilli. In the specimen, they are in the cells, have a large and short shape. In culture, they are usually hedgerows and have a longer body shape.

Arbitrary anaerobic, easy to grow on common culture media, suitable temperature 37 0 C but can also grow at 4 0 C. On normal agar, bacteria grow to form small, round, gray colonies laziness, ball. On blood agar after 48 h of culture, there is a slight hemolytic ring typeb.

Catalase positive, Esculine hydrolysis, Urease negative, H2S negative. Bacteria have O-body antigens and H-hair antigens. Based on these two antigens, Listeria monocytogenes is divided into 4 serotypes I, II, III, and IV, commonly types I and IV. The bacteria do not secrete an exotoxin, but an endotoxin that causes necrosis.

Possibility to cause disease


Bacterial reservoirs include sick animals, healthy animals carrying diseases, milk of chronically infected animals, contaminated food, dust, etc. Bacteria survive in the environment for a long time because of their strength high resistance.

The route of transmission is the gastrointestinal tract, rarely by inhalation. The disease often occurs in embryos, newborns, and the elderly...In newborns, the disease is transmitted through the placenta or when the child enters the mother's genital tract.

Possibility to cause disease in humans

Listeria monocytogenes cause disease in many animals, can be transmitted to humans, mainly in infants but also in adults. They cause meningitis, meningitis - encephalitis, bacteremia, meningitis, conjunctivitis, urinary tract infections... Listeria monocytogenes causing hidden disease is the most common. Pregnant women often present with fever, flu-like syndrome, or urinary tract infection. The disease can be completely silent but reintroduce the infection to the fetus through the placenta and lead to miscarriage or premature birth, and the baby is born with the disease.

Microbiological diagnosis


Specimens are appropriate depending on the subject and the type of disease.

Newborns: cerebrospinal fluid, dung, blood, conjunctivitis fluid...           

In the deceased fetus: necrotic granules of the viscera.

In the mother: fluid, placenta, blood.

Adults: urine, blood, cerebrospinal fluid.

Direct diagnosis

Specimens are directly stained with Gram-positive bacilli, both intracellular and extracellular. Inoculate on blood agar incubated at 40 ° C for bacterial enrichment or on selective media (with nalidixic acid), identify bacteria based on morphology, motility at 20 ° C, catalase-positive active, agglutinating with the antisera Listeria O.

Prevention and cure

Mainly for general disease prevention, pay attention to the use of animal products that must be well sterilized. Early diagnosis of the sick mother for timely treatment.

Treatment: Using antibiotics for a long time (because of intracellular bacteria), usually using penicillin in combination with streptomycin, or using Bactrim, ampicillin... lasting 2-3 weeks, for patients with immunodeficiency, can be used 4-6 weeks.