A clinical diagnosis of meningitis is confirmed with a latex agglutination test on CSF for the capsular polysaccharide of the organism. The most likely causative agent is
**Core Concept**
The latex agglutination test on cerebrospinal fluid (CSF) detects the capsular polysaccharide of the causative agent, which is a key virulence factor for certain bacterial pathogens. This test is particularly useful for identifying encapsulated bacteria that cause meningitis.
**Why the Correct Answer is Right**
The correct answer is likely to be a bacterium with a polysaccharide capsule that is a common cause of bacterial meningitis. The latex agglutination test detects the presence of these capsular polysaccharides in the CSF. The most likely causative agent is *Neisseria meningitidis*, which has a polysaccharide capsule that is a key virulence factor. The capsule is made of a polysaccharide composed of sialic acid and polyribosyl ribitol phosphate, which is detected by the latex agglutination test.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because *Streptococcus pneumoniae* is another common cause of bacterial meningitis, but it is typically identified using a different type of test, such as the Quellung reaction.
**Option B:** This option is incorrect because *Haemophilus influenzae* type b is a common cause of bacterial meningitis, but it is typically identified using a different type of test, such as the direct fluorescent antibody test.
**Option C:** This option is incorrect because *Cryptococcus neoformans* is a fungal pathogen that can cause meningitis, but it is typically identified using a different type of test, such as India ink staining.
**Clinical Pearl / High-Yield Fact**
The latex agglutination test is a rapid and sensitive test for detecting the capsular polysaccharide of *Neisseria meningitidis* in CSF. This test is particularly useful in clinical settings where rapid diagnosis and treatment are essential to prevent complications and improve outcomes.
**Correct Answer:** D.