Gram positive rod, cold tolerant and motile.
Found in most meats, it survives cold. Immunosuppression (AIDS, lymphoma, CLL, steroids), including alcoholism and pregnancy, and age > 50 (PubMed) are important risks as well as eating unpasteurized milk and milk products (like, you know, cheese, including an outbreak from the horribly named headcheese), deli meats, hot dawgs and occasionally fresh vegetables just for any you vegans (CDC), sometimes leading to hospital outbreaks. The solution? Deep fry everything.
There have been 8 hospital outbreaks from "sandwiches (3 reports), butter, precut celery, Camembert cheese, sausage, and tuna salad (1 report each) (PubMed)."
"Compared with persons < 65 years with no underlying conditions, those with chronic lymphocytic leukemia had a .1000-fold increased risk of acquiring listeriosis, and those with liver cancer; myeloproliferative disorder; multiple myeloma; acute leukemia; giant cell arteritis; dialysis; esophageal, stomach, pancreas, lung, and brain cancer; cirrhosis; organ transplantation; and pregnancy had a 100–1000-fold increased risk of listeriosis (PubMed)."
Use of ppi's a risk. (PubMed).
Inflammatory bowel disease also a risk: "12.2 bacteremias/100 000 IBD patient-years, compared with 1.6 bacteremias/100 000 person-years, with an odds ratio of 7.4 (PubMed)."
Biologics (like infliximab) are a disease risk, especially if on concomitant steroids or methotrexate (PubMed). Biologics increase the risk for PJP, but for Listeria, Salmonella, and Legionella and it has been suggested that all patients on biologics be on TMP/Sulfa to prevent all of the above (PubMed).
Alemtuzumab, used for CLL, T cell lymphoma and MS, increases the risk of Listeria (PubMed).
Not all Listeria are the same: genotype ST6 has worse outcomes (PubMed).
In pregnancy there may be certain strains that are prone to causing infection (PubMed).
See the note. Ampicillin PLUS gentamicin has been the standard for years; the use of gentamicin is not exactly proven (PubMed). If penicillin allergic either desensitize OR try high dose TMP/Sulfa (4mg/kg q6). Vancomycin is a last ditch treatment. Linezolid works in the test tube, and there are a smattering of successes.
Dexamethasone may not be of use (PubMed).