Listeria monocytogenes

The bacterium was named after the English surgeon Josef Baron Lister.

Listeria monocytogenes is a saprophytic, gram-positive, non-spore-forming, intracellular, anaerobic bacterium and an opportunistic, foodborne pathogen that can cause listeriosis in humans and animals. Listeria monocytogenes produces a hemolytic exotoxin, but no endotoxins. The bacterium has developed an extraordinary ability to adapt to stressful conditions in different environments, resulting in ubiquitous dissemination. L. monocytogenes is a versatile pathogen that poses a serious threat to humans and livestock and is a challenge for food safety.

L. monocytogenes is the causative agent of listeriosis, a sporadically occurring disease in humans and animals with very high hospitalization and mortality rates, which is considered one of the most serious foodborne diseases. The genus Listeria currently comprises 21 recognized species of ubiquitous small rod-shaped Gram-positive bacteria, of which only Listeria ivanovii and L. monocytogenes are pathogens in mammals (Quereda JJ et al. 2020). Pathogenic species of Listeria have emerged as one of the most important foodborne pathogens in Western countries in the second half of the 20th century, and outbreaks of listeriosis in humans and animals have had a significant economic impact on society and the food industry. Although the genus Listeria was originally a saprophytic bacterium, some species have successfully adapted to various environmental niches associated with human activity, including farms (mammal and bird droppings), food and food processing environments. This stress tolerance also allows Listeria to enter the gastrointestinal tract of mammalian hosts from contaminated food (NicAogáin K et al. 2020).

The genus Listeria currently comprises 21 species of ubiquitous Gram-positive rods found in different environmental niches (Quereda JJ et al. 2020). Two Listeria species, L. monocytogenes and L. ivanovii, have been considered pathogenic in the past (Orsi RH et al. 2016). L. monocytogenes infects animals and humans and is the zoonotic species of greatest global public health and economic importance in its genus. L. ivanovii is considered a pathogen that mainly infects ruminants , as human infections are rare and mainly affect immunocompromised, debilitated patients.

Although L. innocua was originally considered a non-hemolytic and non-pathogenic Listeria species, natural atypical hemolytic isolates have been isolated from various foods. Rare cases of L. innocua sepsis and meningitis have been reported in both ruminants and humans (Walker JK et al. 1994; Moura A et al. 2019). Importantly, atypical hemolytic L. innocua can actively cross the intestinal barrier and invade deeper organs such as the liver and spleen. In addition, some strains of L. innocua carry LIPI-3, a pathogenicity island specific for L. monocytogenes lineage I, which is overrepresented in epidemic listeriosis outbreaks. LIPI-3 encodes a bacteriocin that is highly expressed in the gut to alter the host gut microbiota, enabling colonization of the gut by L. monocytogenes (Moura A et al. 2019). Remarkably, one of these L. innocua strains possessing LIPI-3 was isolated from a human patient with meningitis (Clayton EM et al. (2014). Human exposure to hemolytic L. innocua is rare.

Once L. monocytogenes has entered the host, it develops various mechanisms to invade different eukaryotic cell types, survive intracellularly, evade the immune system and spread throughout the body (Radoshevich L et al. 2018). In addition, this pathogen can cross the blood-brain and placental barrier with consequences for the course of the disease (meningitis, miscarriage). This can have fatal consequences for immunocompromised individuals or pregnant women.

1. Charlier C et al. (2017) Clinical features and prognostic factors of listeriosis: the MONALISA national prospective cohort study. Lancet Infect Dis 17:510-519.
2. Charlier C et al (2020) Maternal-neonatal listeriosis. Virulence 11:391-397.
3. Clayton EM et al. (2014) Atypical Listeria innocua strains possess an intact LIPI-3. BMC Microbiol14:58.
4. Dunphy L et al. (2022) Maternal sepsis caused by Listeria monocytogenes with a fetal outcome. BMJ Case Rep 15:e249989.
5. Eiss HJ et al. (1951) Granulomatosis infantiseptica a general infection in newborns and infants with miliary granulomas. Z Gesamte Inn Med 6:451-457.
6. Gomez G et al. (2022) Neonatal listeriosis: a rare but not-to-be forgotten infection. BMJ Case Rep 15:e243033.
7. Moura A et al. (2019) Atypical hemolytic Listeria innocua isolates are virulent, albeit less than Listeria monocytogenes. Freitag NE, editor. Infect Immun 87:e00758-18.
8. NicAogáin K et al. (2020) The role of stress and stress adaptations in determining the fate of the bacterial pathogen Listeria monocytogenes in the food chain. Front Microbiol 7:1-16.
9. Orsi RH et al. (2016) Characteristics and distribution of Listeria spp., including Listeria species newly described since 2009. Appl Microbiol Biotechnol 100:5273-5287.
10. Quereda JJ et al. (2017) Listeriolysin S: a bacteriocin from epidemic Listeria monocytogenes strains that targets the gut microbiota. In: Gut Microbes 8:384-91.
11. Quereda JJ et al. (2020) Listeria valentina sp. nov., isolated from a water trough and the faeces of healthy sheep. Int J Syst Evol Microbiol 70:5868-5879.
12. Radoshevich L et al. (2018) Listeria monocytogenes: towards a complete picture of its physiology and pathogenesis. Nat Rev Microbiol16:32-46.
13. Walker JK et al. (1994) Listeria innocua isolated from a case of ovine meningoencephalitis. Vet Microbiol 42:245-253.
14. Xu L et al. (2022) Neglected listeria infection in pregnancy in China: 93 cases. J Matern Fetal Neonatal Med 35:9549-9557.
15. Zhang S et al. (2023) Clinical Features and Antibiotic Treatment of Neonatal Listeriosis: A Hospital-Based Study. Infect Drug Resist 16:6647-6659.