Listeriosis

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Etiology/Bacteriology

Taxonomy

Domain: Bacteria
Kingdom: Bacteria
Phylum: Firmicutes
Class: Bacilli
Order: Bacillales
Family: Listeriaceae
Genus: Listeria
Species: monocytogenes

Description

Listeria are gram positive facultative anaerobes observed to be bacilli in short chains. If a direct sample is observed under the microscope, Listeria can resemble cocci shapes and can be mistaken for streptococci. All species produce flagella at room temperature but do not express it at 37 degrees Celsius. These non-spore forming, catalase positive bacteria are found in soil, sewage, stream water and animal carriers.

Pathogenesis

Transmission

Listeriosis can be transmitted by eating food contaminated with the strain Listeria monocytogenes . Due to the long incubation period of 1 to 4 weeks, many animals that provide meat and dairy can be infected with this disease but not show any symptoms. This being the reason why most humans become infected by eating raw or undercooked meat products. Foods that come packaged ready to eat, such as cold cuts and cheeses, can become adulterated with Listeria after the cooking or pasteurization process, but before shipping out. Listeria is able to grow in such a large range of temperatures, that even a refrigerator can provide an environment for reproduction. With this risk being high for prepackaged pregnant women are warned to stay away from these foods because if they contract the disease they can pass it on to their baby. Very rare, but reported cases of Listeria have been acquired through a stay at the hospital.

Virulence factors

1. Adhesion to the surface of mammalian cells. Close interaction between host cells and L. monocytogenes makes invasion possible. Numerous surface adhesion factors allow the pathogen to connect to host cells such as:

• Lap adhesion protein uses an alcohol acetaldehyde dehydrogenase interaction with the host cell receptor, Hsp60, to adhere to intestinal cells. This Lap protein is required for full virulence.
• Ami protein associates to the bacterial surface via its C-terminal cell wall-anchoring (CWA) domain. The CWA allow adhesion to host epithelial cells.
• The gene segment dltA integrates D-alanine-polyphosphoribitol into lipoteichoic acids (LTAs)which contributes to cell adhesion.
• FbpA is expressed on the bacterial surface and binds to stationary host fibronectin. FbpA also helps expression of LLO and InlB (other virulence factor proteins).
• The C-terminus of InlJ has an LPXTG segment which bonds LPXTG-containing proteins to the cell membrane of the host.

2. Invasion of L. monocytogenes also contributes to its virulence. The pathogen can enter into macrophage cells or non-phagocytes.

• InlA and InlA are protiens that assist Listeria entry into non-phagocytes. InlA is a critical player for virulence.
• InlA and E-cadherin interaction allows for epithelial cell invasion because it causes cytoskeletal reorganization.
• Vip protein is present in all pathogenic species and absent in all non-pathogenic strains. Vip mediates Listeria invasion into epithelial cells. The host receptor, Gp96 interacts with Vip and this interaction is important for the entry of eukaryotic cells.
• GtcA mediates glycosylation of host cell wall teichoic acids.
• Listeriolysin O (LLO) helps invasion of host cells because it causes influx of calcium ions which allows for a more effective invasion of Listeria into the cell. 3.Vacuole escape occurs before invasion of non-phagocytic cells and involves the lysis of vacuoles.
  • Listeriolysin O (LLO) has critical role in the escape of L. monocytogenes from vacuoles. This secreted toxin is a cholesterol-dependent cytolysin (CDC). LLO works best in acidic conditions, which occurs inside the vacuole. When LLO is inside the cytoplasm (at neutral pH), activity decreases which lessens host cell damage. Enzymes plcA and plcB work with LLO to enhance lysis of the vacuoles.
  • PrsA2 stabilizes and catalyzes activity of LLO which allows for optimal activity during vacuole escape.
  • SipZ assists in the secretion of LLO
  • SvpA also promotes pathogen escape from the phagosomes.

  Clinical features and Diagnosis

  Treatment

  Listeria is most commonly treated through the use of antibiotics. However, if no or mild symptoms are presented, then no intervention is needed. If a pregnant women is diagnosed with a Listeria an effective regiment of antibiotics is immediately prescribed to try and prevent it from spreading to the fetus. The current antibiotic of choice is ampicillin or a cocktail of ampicillin or gentamicin, although due to allergies and each case being individual, various other antibiotics are efficient in killing this disease.

  Prevention

  The FDA (Food and Drug Administration) has provided the general public with guidelines to prevent Listeria contamination.
  

  • Rinse all produce thoroughly under hot water before consuming, preparing, and even cooking. Even if the skin is going to be peeled off, it needs to be washed to prevent the spread of bacteria.
  • Scrub all produce that is hard, such as melons and potatoes, with a clean brush under hot running water.
  • Dry all rinsed produced with clean towels or paper towels.
  • Separate produce from raw bovine, porcine, and avian meats from cooked meats, produce, and pre-packaged, no preparation needed foods.

  An important step in keeping Listeria free is properly cleaning ones kitchen and all areas raw meats and produce have been stored.

  • So that one does not create a fomite (object that carries disease) all objects that have touched raw meats and produce need to be washed.
  • Keep the refrigerator under 4°C and the freezer less than -18CF to prevent Listeria from being able to grow in that environment.
  • All leakages from raw meats, spoiled produce, and prepackaged foods should be immediately cleaned up with disinfectants and hot water.

  Food Safety is an easy way to prevent infection from Listeria using the following methods.

  • Cooking all bovine (63°C or if ground 71°C), porcine (63°C), and avian meats (74°C) to the proper FDA specified temperatures.
  • Do not let prepackaged food sit in the refrigerator for long periods of time, it is best to ingest these items as close to the date purchased as possible. Examples include hot dogs which unopened can be eaten within 2 weeks of purchase, but if opened should not sit longer than 1 week. Cold cuts should only be eaten within 2 weeks if it is left unopened, but packages that have been opened or cut at the deli need to be eaten no later than 3 to 5 days after purchase.
  • If left overs are to be store in the refrigerator need to be placed in thin bowls that allow for the food to be cooled evenly. If not eaten within 3 to 4 days, these foods need to be thrown away.
  • Stay away from unpasteurized dairy products.

  Host Immune Response

  References

  1. Conway, Tyrrell. “Genus conway”. “Microbe Wiki” 2013. Volume 1. p. 1-2.
  2. http://www.cdc.gov/listeria/
  3. D Cabanes, et al. "The Arsenal Of Virulence Factors Deployed By Listeria Monocytogenes To Promote Its Cell Infection Cycle." Virulence 2.5 (n.d.): 379-394. Science Citation Index. Web. 14 July 2013.
  4. Burkholder KM, Kim KP, Mishra KK, Medina S, Hahm BK, Kim H, et al. Expression of LAP, a SecA2-dependent secretory protein, is induced under anaerobic environment. Microbes Infect 2009; 11:859- 67; PMID:19454322; http://dx.doi.org/10.1016/j. micinf.2009.05.006.

  
  

  Created by Danielle Vinnedge, Naomi Quillin, Jennifer Gallup, students of Tyrrell Conway at the University of Oklahoma.