A 30 year old woman with a bad obstetric history presents with fever. The blood culture from the patient grows gram-positive small to medium coccobacilli that are pleomorphic, occurring in sho chains. Direct wet mount from the culture shows tumbling motility. The most likely organism is:

Woman in the question stem is suffering from infection caused by Listeria monocytogens. Listeria monocytogenes is a food borne pathogen capable of causing parasitic infections in human. It is a motile, non-spore forming, gram positive, rod shaped bacterium. It is a facultative anaerobe and can grow in vaccum, packaged products at refrigerated temperatures. Listeria monocytogenes is widely distributed in nature and has been isolated from soil, water, vegetation, sewage, animal feeds and food processing units. Ref: Jawetz, Melnick and Adelberg's Medical Microbiology, Chapter 12 ; Safety of Meat and Processed Meat, Fidel Toldra, Page 567 ; Sherris Medical Microbiology, 5th Edition, Chapter 25, 26