Introduction
Listeria is a bacterium belonging to the category of bacilli; it is facultative aerobic (survives both in the presence and absence of oxygen), non-sporogenic (does not produce spores), sensitive to acid pH and classified as Gram-positive (Gram +), therefore it is able to produce lipid endotoxins resistant to high temperatures.
Listeria is one of the most relevant food-related 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 become an effective toxinfectious bacterium also for humans.
6 types of listeria are known: listeria monocytogenes, listeria harmless, listeria seeligeri, listeria welshimeri, listeria ivanovii and listeria grayi.
Listeria monocytogenes is capable of causing 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 meats, up to cooked meats (for cross contamination) and preserved vegetables; prefers dairy foods.
The bacterium Listeria monocytogenes seen under the electron microscope. This microorganism is the infectious agent responsible for listeriosis, a food-borne disease that affects 2,500 people in a clinically evident form every year in the United States; of these 500 die
Symptoms
To learn more: Listeriosis Symptoms
Biological characteristics and Contagion
Listeria is an insidious bacterium, as it effectively resists low temperatures (freezing); since the 1980s ", its food contagion has also become common 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 decaying plants and often also in the intestines of wild or farmed animals (sheep, cattle, pigs and poultry). It can be present in contaminated aquifers and from there, through irrigation, settle on vegetables and fruit, furthermore, remaining in watercourses it can determine the contagion of fish and crustaceans. Flies and ticks are carriers of it.
The foods on which listeria survives or multiplies are many and its elimination is almost impossiblerather, the related treatments aim at controlling proliferation, which occurs between 0 and 45 ° C but more rapidly between 30 and 37 ° C; 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 pHs but does not reproduce effectively in acidic 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 takes root effectively on immunosuppressed (AIDS patients, chemotherapists, etc.) and 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 cite alcoholism, neoplasms, diabetes, cardiovascular diseases, etc. NB. The most important complication of a listeriosis serious it is septicemia (bacteria in the bloodstream) resulting in meningitis (infection of the central nervous system - CNS).
Pregnancy
Although listeria may appear almost asymptomatic in the pregnant woman (similar to a mild flu), in the fetus the repercussions can be catastrophic. The fruit of conception is the victim of a "congenital infection, consequently it can undergo: premature birth, death or abortion. Even if listeria infects the newborn during childbirth 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 fatal sepsis and meningitis.
Screening is done with ultrasound and serological tests.
In the affected mother, the pharmacological treatment must be timely and is carried out with a combination of antibiotics (ampicillin and aminoglycoside).
Immune Defense and Treatment
It should be remembered that the control of listeria in the organism is entrusted to T lymphocytes and activated macrophages (some white blood cells), therefore any alteration in these immune cells determines an irreversible worsening of listeriosis. NB. Listeria can evade the immune defenses by proliferating inside mononuclear phagocytes.
Therapy is mainly pharmacological based on: coumermicin, rifampicin, ampicillin and aminoglycoside antibiotics; unfortunately, antimicrobial therapy is not always satisfactory in immunocompromised subjects.
Bibliography
- Food microbiology - J. M. Jay, M. J. Loessner, D. A. Golden - Springer - pag 637: 667
- Sanitation in the food industry - N. G. Marriott, R. B. Gravani - Springer - pages 40-41.
