Introduction
Listeria is a bacterium belonging to the category of bacilli; it is optional aerobic (it survives both in the presence and in the absence of oxygen), non-spore-forming (it does not produce spores), sensitive to acid pH and classified among the gram negative (Gram -), therefore it is able to produce lipid endotoxins resistant to high temperatures .
Listeria is one of the most significant food etiological pathogens; it is characterized by a highly adaptable nature, to the point that, from a bacteriological strain involved exclusively in animal diseases, it has recently been transformed into an effective bacterial toxicant also for human beings.
Six types of listeria are known: listeria monocytogenes, listeria innocua, listeria seeligeri, listeria welshimeri, listeria ivanovii and listeria grayi .
Listeria monocytogenes is able to provoke a food poisoning called listeriosis ; since the 1950s, numerous cases of epidemics and suspected cases probably caused by this listeria have been documented.
The foods responsible for bacterial proliferation seem to be many, starting from raw milk and fresh meat, to cooked meat (due to cross contamination) and to preserved vegetables; prefers dairy-food.
The bacterium Listeria monocytogenes seen under an electronic microscope. This microorganism is the infectious agent responsible for listeriosis, a foodborne disease that in the United States affects 2, 500 people every year in clinically evident form; of these 500 die
Symptoms
To learn more: Symptoms Listeriosis
Biological characteristics and Contagion
Listeria is an insidious bacterium, as it effectively resists low temperatures (freezing); since the 80s, its food contagion has become common also in humans and seems to spread frequently on food due to cross contamination. It is a ubiquitous bacterium; it can be found on the soil, on decomposing plants and often also in the intestines of wild or farmed animals (sheep, cattle, pigs and poultry). It can be present in the contaminated aquifers and from there, through irrigation, resting on vegetables and fruit, moreover, remaining in water courses can cause the infection of fish and crustaceans. Flies and ticks are carriers.
The foods on which the listeria survives or multiplies are many and its elimination is almost impossible, rather, the relative treatments aim to control proliferation, which occurs between 0 and 45 ° C but more rapidly between 30 and 37 ° C; the listeria is also quite resistant to heat (it dies just above 60 ° C) and to sodium chloride which, even at saturation levels, does not stop its growth. Listeria likes neutral or slightly alkaline pH but does not reproduce effectively in acid ones.
People at risk
Listeriosis is NOT a potentially risky disease for the healthy subject, therefore, serious cases are rarely documented. On the contrary, listeria effectively takes root on immunosuppressed (AIDS patients, chemotherapists etc.) and on pregnant women (20 times more at risk than a healthy man); it is clear that other conditions can favor the inauspicious course of listeriosis, we mention alcoholism, neoplasms, diabetes, cardiovascular diseases, etc. NB . The most important complication of severe listeriosis is septicemia (bacteria in the bloodstream) resulting in meningitis (infection of the central nervous system - CNS).
Pregnancy
Although in pregnant women the listeria may appear almost asymptomatic (similar to a slight influence), in the fetus the repercussions can be catastrophic. The fruit of conception is the victim of a congenital infection, consequently it can be subjected to: premature birth, death or abortion. Even if the listeria infects the newborn during delivery there is a high risk of complications; more precisely, after an incubation generally oscillating between 7 days and 4 weeks, the symptomatological picture is characterized by deadly sepsis and meningitis.
Screening is performed with ultrasound and serological tests.
In the affected mother the pharmacological treatment must be timely and is carried out with an association of antibiotics (ampicillin and aminoglycoside).
Immunodefence and Treatment
It should be remembered that the control of listeria in the organism is assigned to T lymphocytes and activated macrophages (some white blood cells), therefore, any alteration of these immune cells causes an irreversible deterioration of listeriosis. NB . Listeria can elude immune defenses by proliferating within mononuclear phagocytes.
The therapy is mainly pharmacological based on: coumermicin, rifampicin, ampicillin and aminoglycosidic antibiotics; unfortunately, in immunocompromised subjects antimicrobial therapy is not always satisfactory.
Bibliography
- Food microbiology - JM Jay, MJ Loessner, DA Golden - Springer - pag 637: 667
- Sanitization in the food industry - NG Marriott, RB Gravani - Springer - pag 40-41.
