Question

a lumbar puncture is performed on an 82 year old woman who is receiving immunosuppressive therapy. the direct gram stain of the csf reveals small gram-positive rods and numerous wbcs. at 18 hours, small translucent colonies with a narrow zone of beta-hemolysis grow on sheep blood agar. the isolate produces catalase. identification of this isolate could be made by demonstration of:_______.

Answer 1

The isolate from the CSF showing small gram-positive rods with beta-hemolysis and a catalase-positive reaction can be identified as Listeria monocytogenes by demonstrating its characteristic tumbling motility and specific antigen presence.

Step-by-step explanation:

Identification of the gram-positive rods in the CSF of an 82-year-old woman on immunosuppressive therapy could be made by demonstrating the presence of the pathogen's unique characteristics. Given the information that the colonies show a narrow zone of beta-hemolysis on sheep blood agar and that the isolate is catalase positive, the identification could likely be Listeria monocytogenes, which is consistent with these findings. Other confirmatory tests, such as checking for motility at room temperature and the presence of specific antigens (e.g., through antibody testing), would help confirm the species.