Listeria monocytogenes (page 3)
(This chapter has 3 pages)
© Kenneth Todar, PhD
Because L. monocytogenes multiplies intracellularly,
is largely protected against circulating immune factors (AMI) such as
and complement-mediated lysis. The effective host response is
immunity (CMI), involving both lymphokines (especially interferon)
by CD4+ (TH1) cells and direct lysis of infected
(Tc) cells. Both of these defense mechanisms are expressed
the microenvironment of the infected foci, which are organized as
characterized by a central accumulation of macrophages with irregularly
shaped nuclei, and by peripheral lymphocytes recognizable by rounded
and a narrow border of intensely staining cytoplasm.
Treatment and Prevention
If diagnosed early enough, antibiotic treatment of pregnant
or immunocompromised individuals can prevent serious consequences of
disease. Antibiotics effective against Listeria species include
ampicillin, vancomycin, ciprofloxacin, linezolid and azithromycin.
However, early diagnosis is the exception rather than the
since the first signs of a case or an outbreak are reports of
or serious infections resembling listeriosis. By then, any cohorts who
have become infected from eating the same food are likely recovered
an inapparent or flu-type infection, or they themselves may have
serious disease. However, processed foods known to be the source of Listeria
that may still be in the market place, restaurant or home should
not be used, and recalls should be imperative. It must also be
recognized that L. monocytogenes is able to grow at low
About 2500 cases of listeriosis occur each year in the United
States. The initial symptoms are often fever, muscle aches, and
sometimes gastrointestinal symptoms such as nausea or diarrhea. The
illness may be mild and ill persons sometimes describe their illness as
flu-like. If infection spreads to the nervous system, symptoms such as
headache, stiff neck, confusion, loss of balance, or convulsions can
occur. Most cases of listeriosis and most deaths occur in adults with
weakened immune systems, the elderly, pregnant women, and newborns.
However, infections can occur occasionally in otherwise healthy
persons. Infections during pregnancy can lead to miscarriages,
stillbirths, and infection of newborn infants. Outbreaks of listeriosis
have been linked to a variety of foods especially processed meats (such
as hot dogs, deli meats, and paté) and dairy products made from
Because pregnant women, older adults, and people with weakened immune
systems are at higher risk for listeriosis, CDC recommends the
following measures for these persons.
- Do not eat hot dogs and luncheon meats unless they are reheated
until steaming hot.
- Avoid cross-contaminating other foods, utensils, and food
preparation surfaces with fluid from hot dog packages, and wash hands
handling hot dogs.
- Do not eat soft cheeses such as feta, brie and camembert cheeses,
blue-veined cheeses, and Mexican-style cheeses such as "queso blanco
fresco." Cheeses that may be eaten include hard cheeses; semi-soft
cheeses such as mozzarella; pasteurized processed cheeses such as
slices and spreads; cream cheese; and cottage cheese.
- Do not eat refrigerated pâtés or meat spreads.
Canned or shelf-stable pâtés and meat spreads may be eaten.
- Do not eat refrigerated smoked seafood, unless it is contained in
a cooked dish, such as a casserole. Canned or shelf-stable smoked
seafood may be
- Do not drink raw (unpasteurized) milk or eat foods that contain
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