Microorganisms of the genus Listeria are widely distributed in nature,
although with a limited number of species of medical and veterinary
significance.
Listeria monocytogenes is an important human pathogen that
can cause serious illnesses, with high mortality rates in
susceptible individuals such as the elderly and people with
immuno-compromised conditions.
It is a bacterium that is common in the environment and can be found in
agricultural and food-processing settings, where it tends to persist
once established. It might affect only the gastrointestinal tract, but
may invade other parts of the body, potentially causing septicemia,
meningitis, encephalitis, spontaneous abortion, and stillbirth.
Consumption of contaminated dairy products has been associated
with cases and outbreaks of human listeriosis. Dairy products
are good substrate for L. monocytogenes growth, as they
contain proteins, lactose and trace elements. Outbreaks have been
strongly associated with cheese consumption.
Fresh cheeses, which have been linked to human listeriosis outbreaks in the United States, are considered high-risk foods for L. monocytogenes contamination.
Fresh cheeses are usually protected from contamination by refrigeration
and usually packed with paper or shrink-wrapped with polyethylene or
polypropylene with potential risk of proliferation of aerobic mesophilic
bacteria, coliforms, molds or yeast.
Although L. monocytogenes is effectively inactivated by
pasteurization, the prevention of post-processing contamination of milk
products is of particular importance to dairy industries.
Listeria in cheese
