This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Bacteriology, Subject name: Microbiology
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: 
Select and explain. 
A. Listera monocytogenes, B. Corynebacterium sp., C. Enterococcus sp., D. Erysipelothrix rhusiopathiae
A: Listera monocytogenes
Answer: A: Listera monocytogenes 
Explanation: Listeria are small gram positive coccobacilli with characteristic tumbling motility. They are non motile at 38 degree Celsius as the flagellae are produced optimally at 20-30 degree Celsius. Reference: Ananthanarayan and Paniker&;s Textbook of Microbiology Tenth edition