Listeriosis is an infection, caused by a bacterium known as Listeria monocytogenes. An individual can be infected through the consumption of Listeria-infested food; senior citizens, patients with a weakened immune system and newborn children are the most high-risk population groups.
L. monocytogenes is a bacterial agent that leads to two separate clinical manifestations, depending on the age and immunological status of the infected individual.
To begin with, listeriosis presents with a clinical picture of food poisoning accompanied by fever in otherwise healthy individuals. Symptoms derived from the invasion of the gastrointestinal tract predominate and the disease recedes after some time, similar to food poisoning from other pathogens. Contrary to this, people of younger or older ages (senior population and newborns), people who are immunocompromised and women who are pregnant exhibit symptoms of a more profound illness that includes meningoencephalitis and septicemia, when infected with the microorganism.
Specifically with regard to neonates, listeriosis can either be diagnosed within less than 5 days after birth (early onset) or within a period of time that exceeds the 5-days limit (late onset). The manifestations differ according to the type of neonate listeriosis: early onset infection leads to meningitis and septicemia, while late onset disease is more commonly associated with purulent meningitis. Neonates usually present with an irregular temperature fluctuation, respiratory imbalance, lethargy and poor appetite, while appearing irritable, tachypnoic and prone to epileptic phenomena. The typical histopathological characteristic of listeriosis is the presence of a rash that is identified as containing granulomatous nodules.
In order to diagnose a Listeria infection, the culprit has to be isolated from samples that should, under normal conditions, be completely sterile. For this reason, blood and cerebrospinal fluid cultures are the first samples provided from testing. Depending on the affected regions, other fluids can prove helpful: joint fluid, pericardial and pleural fluid, alongside the amniotic fluid and placenta can be used in order to identify a suspected Listeria infection. In case the brain or hepatic regions appear affected, a magnetic resonance imaging scan or a computerized tomography scan can be performed, in order to detect possible abscesses.
Given that listeriosis can prove fatal to the population groups that are most sensitive to the infection, every pregnant woman who presents with fever and symptomatology compatible with food poisoning should undergo a blood culture in order to exclude this specific infection.
Newborns are amongst the individuals who are expected to develop severe complications from listeriosis, if the infection remains undiagnosed or treated inappropriately. For these reasons, a neonate diagnosed with listeriosis should receive adequate antimicrobial coverage and supportive cardiovascular, pulmonary and nutritional care and monitoring. Extremely complicated cases of listeriosis in newborns should be mandatorily treated in an intensive care unit.
The most effective antimicrobial agents against listeria are those that are able to penetrate the host's cellular barrier and achieve concentrations high enough in order to combat the pathogen. Adherence to the microorganism's PBP3 (penicillin-binding protein 3) is necessary, so as to eradicate the bacterium. Especially for cases diagnosed during pregnancy, the antibiotic has to possess the ability to surpass the placental barrier as well.
Ampicillin is the drug of choice and it is administered simultaneously with an antibiotic of the aminoglycoside group, most commonly gentamicin. The dosage depends on the age, gestational or not, and the severity of the clinical picture. Penicillin G can also be administered as an alternative to ampicillin and Sulfamethoxazole/Trimethoprim as a second alternative therapeutic approach in cases of penicillin hypersensitivity.
Prognosis relies upon the presence of complications such as meningitis, hydrocephalus or shock. Although there are protocols for the treatment of Listeria-induced meningitis , other manifestations, such as rhombencephalitis or the spread of the infection to the cranial nerves   are still markedly grim prognostic factors.
Listeria monocytogenes is a bacterium responsible for the infection known as listeriosis. The pathogen can be contracted from various sources, but food is the most common of all. Soft cheese, milk that has not undergone pasteurization, dairy products, uncooked, unwashed vegetables, as well as beef and poultry that are not maintained in the correct circumstances are substrates on which listeria can ideally reproduce. Its proliferation is facilitated in cold temperatures (4-10°C) and ingestion of infected products suffices for the infection to be initiated.
Listeriosis is a rather rare medical entity. it is believed that only 3 cases per million people are diagnosed each year. Paradoxically, 700 individuals were found to have listeriosis in the USA in the year 2004.
The infection's frequency may be scarce, but it escalates amongst particular groups which display a diminished immunological response. Pregnant women are more susceptible to Listeria monocytogenes, as the prevalence seems to be approximately 12 per 100,000 women. Elderly individuals and other patients whose immune system has been weakened due to various causes (pharmacologic treatment, congenital diseases, other co-infections) are in a greater risk of contracting the bacterium too. In fact, mortality seemed to be particularly high between 2009 and 2011; every patient who succumbed due to listeriosis-induced complications belonged to one of the aforementioned high-risk groups .
With regard to newborns, the infection can start to be symptomatic within less than 5 days after birth (early onset) or within more than 5 days after birth, in which case it is termed as late onset. The early onset infection type is accompanied by an extremely high mortality rate amongst newborn children as well , a rate that is believed to reach up to 40%.
Any individuals can be infected with Listeria monocytogenes after ingesting food which is infected with the pathogen, such as inappropriately preserved poultry or meat in general, raw vegetables that have not been adequately cleaned and seafood.
Patients are expected to develop the first symptoms and sings within 1 day, with reference to a food poisoning, and after an average period of a month, when we refer to meningitis, encephalitis or bacteremia.
Concerning the acquisition of the microbe by a newborn baby, this can occur via two pathways: either by transplacental transmission, or by an infected birth canal (vaginal canal)  , although the latter way is less common.
The infection is initiated with the translocation of bacteria from the intestine to the visceral organs, with the liver being the first target. Bacterial proliferation occurs within the hepatic region until an immunological reaction starts. In otherwise healthy individuals, the infection is self limited; since Listeria monocytogenes is often found in products one consumes, the organism possesses memory T cells against the microorganism. Individuals belonging to the high-risk groups, however, exhibit a decline in their defense mechanisms, which leads to the system's inability to hinder the profound reproduction of bacteria in the liver. Thus, severe complications and extensive disease are rendered possible.
It is widely known that all types of products an individual can eat contain a certain number of Listeria pathogens, especially processed products . The most common food products associated with a Listeria infection include soft cheeses, processes products that have not received the necessary degree of sterilization or preservation, wrong pasteurization techniques and vegetable products that are consumed without rinsing them before.
All individuals can be protected from such an infection, by following basic hygienic advice with regard to the maintenance and cooking of food, such as cooking meat products for a considerable amount of time, not allowing for uncooked meat to be in contact with cooked products and washing one's hands after touching uncooked meat. Surfaces have to be adequately cleaned after raw poultry or meat in general have been in contact with them. High-risk people such as pregnant women should not consume soft cheese or delicatessen products during pregnancy, unless the latter have been heated in high temperatures.
Listeriosis is an infection that is not frequently diagnosed in everyday clinical practice. The etiologic agent behind this infection is Listeria monocytogenes, which is a facultative anaerobic bacterium  . It is usually isolated from contaminated food, soil, wood and decaying natural materials. It has also been found in processed meat products, dairy products, raw vegetables that have not been cleaned, and seafood. Listeriosis is particularly common amongst women who are expecting, older patients and individuals with a dysfunctional immunological response.
In some occasions, listeriosis can cause a potentially lethal type of food poisoning; the most dangerous complication is the expansion of the infection to the brain. It has been estimated that listeriosis-induced death occurs in approximately 1/3 of the patients.
Listeriosis is a type of infection caused by a specific bacterium, Listeria monocytogenes. L. monocytogenes typically resides in various locations: the soil, raw vegetables, uncooked meat or meat preserved under the wrong circumstances, milk that has not been pasteurized well or dairy products produced from this milk. Soft cheeses are more frequently linked to listeria infections in comparison to other cheese types and ready delicatessen meals can also contain the bacteria, if their processing has not been conducted in the correct way.
Listeriosis can cause two types of symptoms, depending on how strong the patient's immune system is. In healthy individuals, it causes food poisoning with relevant symptomatology, such as diarrhea, vomiting and nausea. People whose immune system is weakened, however, tend to develop severe disease, including meningitis, encephalitis (infection of the brain matter) and sepsis, namely the spreading of the bacteria in the bloodstream. People who are more susceptible to a severe listeria infection include newborn kids whose immune system has not yet matured, older people, pregnant women and generally immunocompromised patients, either due to a congenital disease, transplantation etc. These groups suffer from an infection of the meninges, brain and an extensive infection of the internal organs which can possibly lead to death.
Listeriosis can be diagnosed when the Listeria pathogen is detected in the blood, the spinal fluid, the joint or pleural fluid as well as in other locations. It is a treatable condition, for which antibiotics such as ampicillin or gentamicin are used.