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.

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.