Which test is recommended for initial differentiation of Listeria monocytogenes from group B streptococci?

The initial differentiation of Listeria monocytogenes from group B streptococci can be effectively achieved through the use of Gram staining, assessment of motility at room temperature, and catalase testing.

When performing a Gram stain, Listeria monocytogenes appears as small, Gram-positive bacilli, while group B streptococci, such as Streptococcus agalactiae, are typically observed as Gram-positive cocci in chains. This basic staining technique provides immediate visual differentiation based on cell morphology and arrangement.

Motility testing is particularly useful, as Listeria is known for its unique characteristic of exhibiting motility at room temperature, a trait not shared by group B streptococci. At temperatures below the human body temperature, Listeria often displays a characteristic tumbling motility when observed under a microscope. This motility can help confirm the presence of Listeria following initial Gram staining.

Catalase testing also plays a significant role in differentiation. Listeria monocytogenes is catalase-positive, which means it produces the enzyme catalase and will bubble when hydrogen peroxide is added. In contrast, group B streptococci are catalase-negative and will not produce bubbling. This reaction serves