Comparison of genetic variations between high- and low-risk Listeria monocytogenes isolates using whole-genome de novo sequencing

The gram-positive bacterium Listeria monocytogenes is the causative agent of listeriosis, a highly fatal opportunistic foodborne infection. Pregnant women, neonates, the elderly, and debilitated or immunocompromised patients in general are predominantly affected, although the disease can also develop in normal individuals. Clinical manifestations of invasive listeriosis are usually severe and include abortion, sepsis, and meningoencephalitis. Listeriosis can also manifest as a febrile gastroenteritis syndrome. In addition to humans, L. monocytogenes affects many vertebrate species, including birds. Listeria ivanovii, a second pathogenic species of the genus, is specific for ruminants. Our current view of the pathophysiology of listeriosis derives largely from studies with the mouse infection model. Pathogenic listeriae enter the host primarily through the intestine. The liver is thought to be their first target organ after intestinal translocation. In the liver, listeriae actively multiply until the infection is controlled by a cell-mediated immune response. This initial, subclinical step of listeriosis is thought to be common due to the frequent presence of pathogenic L. monocytogenes in food. In normal individuals, the continual exposure to listerial antigens probably contributes to the maintenance of anti-Listeria memory T cells. However, in debilitated and immunocompromised patients, the unrestricted proliferation of listeriae in the liver may result in prolonged low-level bacteremia, leading to invasion of the preferred secondary target organs (the brain and the gravid uterus) and to overt clinical disease. L. monocytogenes and L. ivanovii are facultative intracellular parasites able to survive in macrophages and to invade a variety of normally nonphagocytic cells, such as epithelial cells, hepatocytes, and endothelial cells. In all these cell types, pathogenic listeriae go through an intracellular life cycle involving early escape from the phagocytic vacuole, rapid intracytoplasmic multiplication, bacterially induced actin-based motility, and direct spread to neighboring cells, in which they reinitiate the cycle. In this way, listeriae disseminate in host tissues sheltered from the humoral arm of the immune system. Over the last 15 years, a number of virulence factors involved in key steps of this intracellular life cycle have been identified. This review describes in detail the molecular determinants of Listeria virulence and their mechanism of action and summarizes the current knowledge on the pathophysiology of listeriosis and the cell biology and host cell responses to Listeria infection. This article provides an updated perspective of the development of our understanding of Listeria pathogenesis from the first molecular genetic analyses of virulence mechanisms reported in 1985 until the start of the genomic era of Listeria research. Show more

The gram-positive bacterium Listeria monocytogenes is an ubiquitous, intracellular pathogen which has been implicated within the past decade as the causative organism in several outbreaks of foodborne disease. Listeriosis, with a mortality rate of about 24%, is found mainly among pregnant women, their fetuses, and immunocompromised persons, with symptoms of abortion, neonatal death, septicemia, and meningitis. Epidemiological investigations can make use of strain-typing procedures such as DNA restriction enzyme analysis or electrophoretic enzyme typing. The organism has a multifactorial virulence system, with the thiol-activated hemolysin, listeriolysin O, being identified as playing a crucial role in the organism's ability to multiply within host phagocytic cells and to spread from cell to cell. The organism occurs widely in food, with the highest incidences being found in meat, poultry, and seafood products. Improved methods for detecting and enumerating the organism in foodstuffs are now available, including those based on the use of monoclonal antibodies, DNA probes, or the polymerase chain reaction. As knowledge of the molecular and applied biology of L. monocytogenes increases, progress can be made in the prevention and control of human infection. Show more

Abstract This mini review focuses on foodborne illnesses and outbreaks caused by food-producing animals because statistical information of the foodborne illnesses is important in human health and food industry. Contaminated food results in 600 million cases of foodborne diseases and 420,000 deaths worldwide every year. The world population is currently 7.8 billion, and 56 million people die every year; of these, every year, 7.69% of people experience foodborne diseases, and 7.5% of annual deaths (56 million deaths) was died by foodborne illness in the world. A majority of such patients are affected by norovirus and Campylobacter. Listeria monocytogenes is the most fatal. In the United States, except for those caused by Campylobacter, the number of foodborne diseases did not decrease between 1997 and 2017, and cases caused by Toxoplasma gondii are still being reported (9 cases in 2017). The percentage of foodborne illnesses caused by food-producing animals was 10.4%–14.1% between 1999 and 2017 in the United States. In Europe, foodborne illnesses affect 23 million people every year and cause approximately 5,000 deaths. Europe has more Campylobacter- and Salmonella-related cases than in other countries. In Australia, the highest number of cases are due to Campylobacter, followed by Salmonella. In Korea, Escherichia coli followed by norovirus. Campylobacter- and Clostridium perfringens-related cases have been reported in Japan as well. This review suggests that Campylobacter, Salmonella, L. monocytogenes, and E. coli, which are usually isolated from animal-source food products are associated with a high risk of foodborne illnesses. Show more