Okay, let's tackle this question. The patient is a 30-year-old woman with a bad obstetric history and fever. The blood culture shows gram-positive coccobacilli, pleomorphic, in short chains, and tumbling motility.

First, I need to recall the organisms that fit these characteristics. Gram-positive coccobacilli in short chains. Tumbling motility is a key clue. The tumbling motility is classic for Corynebacterium species. But wait, Corynebacterium diphtheriae is more associated with pharyngitis, not sure about obstetric issues. However, there's another Corynebacterium, like C. jeikeium, which is part of the skin flora and can cause infections in immunocompromised individuals. But the question mentions a bad obstetric history. Maybe Listeria monocytogenes? Wait, Listeria is a gram-positive bacillus, not coccobacillus. Wait, Listeria does have tumbling motility. Wait, but Listeria is a bacillus, so maybe not. Let me check again. The question says coccobacilli. Coccobacilli are short rods or round-ended rods, so maybe it's a coccobacillus. But Listeria is a gram-positive bacillus, which can have a coccobacillary form. Oh, right! Listeria monocytogenes can appear as gram-positive coccobacilli and have tumbling motility. That's a key point. Listeria can cause septicemia in pregnant women, leading to bad obstetric outcomes like miscarriage or stillbirth. So the correct answer would be Listeria monocytogenes.

Now, the other options. If the options were, say, C. diphtheriae, E. coli, or Listeria. Let's see. C. diphtheriae is a gram-positive rod but doesn't have tumbling motility. E. coli is gram-negative. Listeria is the one with tumbling motility. So the correct answer is Listeria monocytogenes. The bad obstetric history is a clue for Listeria infection during pregnancy. The tumbling motility is a key feature here. So the options might include other coccobacilli like C. jeikeium but they don't have the same clinical presentation. So I think the answer is Listeria monocytogenes.

**Core Concept**
The question tests identification of *Listeria monocytogenes*, a gram-positive coccobacillus with tumbling motility, commonly associated with pregnancy-related sepsis and poor obstetric outcomes. Key features include pleomorphism, short-chain arrangement, and flagellar-driven motility in liquid media.

**Why the Correct Answer is Right**
*Listeria monocytogenes* is a gram-positive coccobacillus that exhibits characteristic tumbling motility due to flagellar movement, especially in liquid cultures. It is a known pathogen in immunocompromised hosts and pregnant women, causing listeriosis with septicemia, meningitis, or intrauterine infection. The organism’s cell wall lacks a strong peptidoglycan layer, making it appear variable under microscopy (pleomorphism). Pregnancy-related infections often lead to miscar

✓ Correct Answer: A. Listera monocytogenes