Listeria is a bacterial genus containing six species. Named in honour of Joseph Lister, Listeria species are Gram
positive bacilli and are typified by L. monocytogenes, the causative agent of Listeriosis.
Listeria: cause Abortion, stillbirth, preterm labor, sepsis, meningitis, CNS infection, diarrheal disease,
Necrotizing ring ulcer "flesh eating", antibiotic resistance Causes “circling disease” in cattle and death.
Listeria monocytogenes is a special problem since it can survive adverse conditions. It can grow in a pH range of 5.0-
9.5 in good growth medium. The organism has survived the pH 5 environment of cottage cheese and ripening cheddar.
It is salt tolerant surviving concentrations as high as 30.5 percent for 100 days at 39.2 degrees F, but only 5 days if
held at 98.6 degrees F.
The key point is that refrigeration temperatures don not stop growth of Listeria. It is capable of doubling in numbers
every 1.5 days at 39.5 degrees F. Since high heat, greater than 170 degrees F, will inactivate the Listeria organisms,
post-process contamination from environmental sources then becomes a critical control point for many foods. Since
Listeria will grow slowly at refrigeration temperatures, product rotation becomes even more important.
L. ivanovii is a pathogen of ruminants, and can infect mice in the laboratory, although it is only rarely the cause of
Listeriosis is a bacterial infection caused by a gram-positive, motile bacterium, Listeria monocytogenes. Listeriosis is
relatively rare and occurs primarily in newborn infants, elderly patients, and patients who are immunocompromised.
Incidence is 7.4 cases per million population. Annually, 1850 cases are reported in the U.S.. Pregnant women account
for 27% of all cases. Of all nonperinatal infections, 70% occur in immunocompromised patients.
L monocytogenes can often be cultured from the blood, and always cultured from the CSF.
There are four distinct clinical syndromes:
*Infection in pregnancy: Listeria can proliferate asymptomatically in the vagina and uterus. If the mother becomes
symptomatic, it is usually in the third trimester. Symptoms include fever, myalgias, arthralgias and headache. Abortion,
stillbirth and preterm labor are complications of GU infection.
*Neonatal infection (granulomatosis infantisepticum): There are two forms. One, an early-onset sepsis, with Listeria
acquired in utero, results in premature birth. Listeria can be isolated in the placenta, blood, meconium, nose, ears, and
throat. Another, late-onset meningitis is acquired through vaginal transmission, although it also has been reported with
*CNS infection: Listeria has a predilection for the brain parenchyma, especially the brain stem, and the meninges.
Mental status changes are common. Seizures occur in at least 25% of patients. Cranial nerve palsies, encephalitis,
meningitis, meningoencephalitis and abscesses can all occur.
*Gastroenteritis: L monocytogenes can produce food-borne diarrheal disease, which typically is noninvasive. The
median incubation period is 1-2 days, with diarrhea lasting anywhere from 1-3 days. Patients present with fever,
myalgias, muscle aches, gastrintestinal,nausea or diarrhea, headache, stiff neck, confusion, loss of balence, or
Listeria: L. monocytogenes has been implicated in several food poisoning epidemics. The bacterium usually causes
septicema and meningitis in patients with supressed immune function. It also causes listeriosis which is an inflammation
of the brain. Those at high risk include newborns, pregnant women and their fetuses, the elderly, and persons lacking
a healthy immune system.
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