Listeria monocytogenes is a gram positive bacilli that can be grown from blood cultures. It is commonly food-borne and found in contaminated dairy products.
It can cause a meningitis that has a high morbidity/mortality and occurs mainly in more susceptible patients e.g. pregnant, elderly (>55), infants, alcoholics, immunocomprimised etc.
It is mainly associated with a bactaraemic illness and is treated with IV ampicillin/ amoxicillin (as the organism is intrinsically resistant to ceftriaxone).