A culture showing short gram-positive bacilli with no hemolysis and negative catalase suggests which organism?

The presence of short gram-positive bacilli with no hemolysis and negative catalase activity strongly suggests the organism Erysipelothrix rhusiopathiae. This bacterium is known for its characteristic morphology and is non-hemolytic on blood agar, which aligns with the observation from the culture. Additionally, Erysipelothrix rhusiopathiae is catalase-negative, which further supports its identification based on the described culture characteristics.

Other organisms mentioned in the choices possess different properties that set them apart. For instance, Bacillus cereus and Bacillus subtilis are known for being catalase-positive, and Bacillus cereus can also show hemolysis, which does not match the conditions given in the culture. Listeria monocytogenes, while a gram-positive bacillus that can show hemolytic activity on blood agar, is typically characterized by different biochemical properties, including being catalase-positive and motile, which does not align with the parameters of this question. Hence, the unique attributes of Erysipelothrix rhusiopathiae make it the most fitting organism based on the details provided.