A one-week-old baby develops nuchal rigidity and fever. A lumbar puncture is performed and the cerebrospinal fluid demonstrates large numbers of neutrophils. Which of the following is the most likely causative agent?

The nuchal rigidity (stiff neck) suggest meningitis. Numerous neutrophils in the cerebrospinal fluid suggests a bacterial pathogen. The best answer of those listed is Escherichia coli, which is normally a gut organism, but can infect neonates who acquire the organism during passage through the bih canal. Coxsackievirus is a cause of acute lymphocytic meningitis. Herpes virus is a cause of lymphocytic meningitis. Mycobacterium tuberculosis is a cause of chronic meningitis.