Meningitis is an inflammation of the meninges—the three layers of protective membranes that line the spinal cord and the brain. Meningitis can occur when there is an infection near the brain or spinal cord, such as a respiratory infection in the sinuses, the mastoids, or the cavities around the ear. Disease organisms can also travel to the meninges through the bloodstream. The first signs may be a severe headache and neck stiffness followed by fever, vomiting, a rash, then convulsions leading to loss of consciousness.

To diagnose meningitis, a sample of spinal fluid must be drawn from the lumbar region of the spine, a procedure known as a spinal tap. The spinal fluid is examined to reveal the microorganisms present in it. A diagnosis of bacterial meningitis requires immediate treatment with antibiotics.

The meningococcus bacteria, Neisseria meningitides, is a diplococcus that cannot move on its own...