In the last few days, your favorite ice cream (BLUE BELL!) and your favorite hummus (SABRA!) have been recalled due to concerns for contamination with Listeria. Time to get a handle on the situation by learning the basics of this food-borne pathogen.
- Listeria monocytogenes is a gram-positive foodborne pathogen that is ubiquitously found in diverse environments such as soil, water, various food products, animals, and humans
- The bacteria are readily inactivated at pasteurization temperature, the main source of infection represents contaminated raw food that is subjected to minimal further processing, such as soft cheeses, vegetables, and postprocessed contaminated milk products (ICE CREAM!)
- Ingestion of food contaminated with monocytogenes is the usual mode of transmission leading to listeriosis.
- Characterized by bacteremia and meningoencephalitis in individuals with impaired cell-mediated immunity
- Represents one of the most deadly bacterial infections due to its high mean mortality rate of 20%–30%, despite early antibiotic treatment.
- In contrast to the severe invasive disease recent outbreaks demonstrated that infection of healthy individuals with monocytogenes often leads to the development of a febrile gastroenteritis.
- The organisms are well adapted to the conditions in the gastrointestinal tract; the finding that the bacteria are able to colonize and persist in the gallbladder suggests the occurrence of long-term and chronic infections and demonstrates the ability of pathogenic Listeria to survive within the various microenvironments of the gastrointestinal tract.
- Facultative intracellular organism:
- The diverse clinical manifestations of infection with monocytogenes reflect its ability to cross three tight barriers in the human host.
- Following ingestion, monocytogenes crosses the intestinal barrier by invading the intestinal epithelium, thereby gaining access to internal organs.
- During severe infections, crossing the blood–brain barrier results in infection of the meninges and the brain, and in pregnant women, crossing the fetoplacental barrier leads to infection of the fetus.
- Invasive Clinical Syndromes:
- Bacteremia: most common manifestation in immunocompromised patients – similar to other forms of bacteremia, including fever, myalgias, sepsis, etc. May have a prodrome of diarrhea and nausea. The observed symptoms like fever as well as occasionally bloody diarrhea and bacteremia further support the hypothesis that diarrhea results from direct invasion of monocytogenes to the intestinal mucosal epithelium.
- Meningoencephalitis: more common in neonates and adults over 60 years of age. Listeria has a predilection for the brainstem and meninges. Flu-like prodrome possible. Can present with altered mentation, muscle contractions, personality changes, seizures, and other typical signs of meningitis. Brain abscess can occur in up to 10% of patients. Would expect a lymphocytosis on CSF analysis.
- Pregnancy: highest risk of infection is during the third trimester, associated with depressed cell-mediated immunity. Often manifests with an acute febrile illness, myalgias, arthralgias, headache, and backache. Can result in stillbirth or neonatal death.
- Infective Endocarditis
- Non-invasive Clinical Syndrome:
- Febrile Gastroenteritis: Incubation period is typically short (6 hours to 10 days). Common symptoms observed in the effected patients included fever, watery diarrhea, nausea, headache, and pain in joints and muscles. No testing is recommended unless the patient is in a specific high-risk group (i.e. pregnant, immunocompromised, neonates).
- Culture: from CSF, blood, or other body fluids; grows on Muller-Hinton agar with sheep blood . Can see small zone of hemolysis underneath the colony.
- Antibody testing has not proven useful
- 1st line: ampicillin ≥ 6 g/d IV plus gentamicin (if patient > 50 y, chronic disease, cardiovascular or respiratory compromise) x 14 total days up to 6 weeks if endocarditis.
- 2nd line: erythromycin 4 g/d, or TMP/SMX 200–320 mg, or vancomycin 1 g tid x 14 total days.
- Acute Meningitis
- 1st line: ampicillin ≥ 6 g/d IV plus gentamicin (if patient > 50 y, chronic disease, cardiovascular or respiratory compromise) x 21 total days (4-6 weeks if brain abscess)
- 2nd line: Second-line: TMP/SMX 200–320 mg x 21 total days (4-6 weeks if brain abscess)
- Bacteremia in pregnancy
- 1st line: ampicillin ≥ 6 g/d IV x 7–14 total days; if fetus survives, consider longer treatment
- 2nd line: erythromycin 4 g/d IV x 7–14 total days; if fetus survives, consider longer treatment
- Gastroenteritis: supportive care
-Markus Schuppler and Martin J. Loessner, “The Opportunistic Pathogen Listeria monocytogenes: Pathogenicity and Interaction with the Mucosal Immune System,” International Journal of Inflammation, vol. 2010, Article ID 704321, 12 pages, 2010.
–Nature Reviews Microbiology4, 423-434(June 2006)
-Rev Obstet Gynecol. 2008 Fall; 1(4): 179–185.