amongst B. cereus, S. aureus, S. sp, and L. monocytogenes, which two cannot be separated on the basis of morphology or gram reaction? Why? Solution Among B. cereus, S. aureus and L. monocytogenes, B. cereus and L. monocytogenes are rod shaped, while S. aureus is a round shaped bacterium. all the three are Gram positive. therefore, B. cereus and L. monocytogenes can not be separated..