Use the following choices to answer questions 9 and 10:
a. Cryptococcus
b. Haemophilus
c. Listeria
d. Naegleria
e. Neisseria


Microscopic examination of cerebrospinal fluid reveals gram-positive rods.

Verified step by step guidance

1. Identify the characteristics of the organism based on the microscopic examination results.
2. Note that the organism is described as gram-positive rods.
3. Review the list of choices provided: Cryptococcus, Haemophilus, Listeria, Naegleria, Neisseria.
4. Recall that Listeria is known to be a gram-positive rod.
5. Match the characteristics of Listeria with the description given in the problem to determine the correct answer.

Key Concepts

Gram Staining

Gram staining is a fundamental laboratory technique used to classify bacteria based on their cell wall composition. Bacteria that retain the crystal violet stain appear purple and are termed Gram-positive, while those that do not retain the stain appear pink and are termed Gram-negative. This distinction is crucial for identifying bacterial species and determining appropriate treatment options.

Cerebrospinal Fluid (CSF) Analysis

Cerebrospinal fluid analysis involves examining the fluid surrounding the brain and spinal cord to diagnose infections, inflammation, or other neurological conditions. The presence of specific bacteria, such as Gram-positive rods, can indicate particular infections, guiding clinicians in selecting the right antimicrobial therapy and understanding the underlying pathology.

Bacterial Morphology

Bacterial morphology refers to the shape, size, and arrangement of bacterial cells, which can provide important clues for identification. Gram-positive rods, for instance, can include various genera such as Listeria and Bacillus. Understanding these morphological characteristics helps microbiologists differentiate between species and understand their potential pathogenicity.