A baby born at 32 weeks gestation with Apgar scores of 2 and 7 was placed in the neonatal intensive care unit.She developed a fever and leukocytosis; lumbar puncture revealed pleocytosis with increased protein, decreased glucose, and gram-positive rods. Which one of the following organisms was most likely isolated from the CSF?
The three major causes of neonatal meningitis are group B streptococci (Streptococcus agalactiae), Escherichia coli, and Listeria monocytogenes. All can be found in the vaginal tract of normal women and may contaminate the infant during passage through the bih canal. They colonize the upper respiratory tract and can cause pneumonia, septicemia, and/or meningitis in the neonate. They are readily distinguished on morphological grounds; the streptococci are gram-positive cocci in chains, E. coli is a gram-negative rod, and L. monocytogenes is a gram-positive pleomorphic rod. There are other gram-positive rods that resemble Listeria (e.g., the diphtheroid bacilli found in the upper respiratory tract and on the skin), hence a motility test is done to confirm the identification. L. monocytogenes is motile at room temperature but not when grown at 37 degrees C. L. monocytogenes is also associated with drinking unpasteurized milk. Neisseria meningitidis is the most common cause of meningitis in school-age children and young adults. It is a fastidious, non-motile, gram-negative diplococcus that would be a very rare cause of meningeal disease in very young patients, such as this one. Ref: Ray C.G., Ryan K.J. (2010). Chapter 26. Corynebacterium, Listeria, andBacillus. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.
Escherichia coli
Listeria monocytogenes
Neisseria meningitidis
Streptococcus agalactiae