This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.N.S, Subject name: Medicine
A 25 year male presented with high grade fever, headache, neck stiffness, on examination found to have neck rigidity, kernig's sign positive, csf analysis showed neutrophilic predominance, low glucose and limulus amebocyte lysate assay was positive. Which of the following is the likely pathogen? 
Select and explain. 
A. Staphylococcus aureus, B. Streptococcus pneumonia, C. Neisseria meningitides, D. Listeria monocytogenes
C: Neisseria meningitides
Answer: C: Neisseria meningitides 
Explanation: The Limulus amebocyte lysate assay is a rapid diagnostic test for the detection of gram-negative endotoxin in CSF and thus for making a diagnosis of gram-negative bacterial meningitis. The test has a specificity of 85-100% and a sensitivity approaching 100%. Thus, a positive Limulus amebocyte lysate assay occurs in viually all patients with gram-negative bacterial meningitis, but false positives may occur. Ref Harrison 20th edition page 1001