Lab 2: CNS infections and CSF

This week in lab we continued our focus of sterile fluids by examining cerebral spinal fluid.  Were all given a case study and a CSF specimen in order to determine what type of infection was present.  My case involved a 65 year old man who was admitted to the hospital in a coma.  His symptoms included a fever and stiffness in the neck.  He did not respond to verbal commands but did respond to painful stimuli to his leg. 

My first step was to perform a gram stain.  After examining the slide I gave the specimen a quantitation grade of 4+ meaning there were more than 30 per oil immersion field.   The gram stain showed gram positive rods forming palisades. Some rods formed short chains and pairs in the form of “L” and “V” letters. 

Gram stain of CSF specimen

I then examined the SBA and chocolate agar plates for growth.  Both showed small, translucent gray colonies.  The colonies that grew on sheep blood agar showed a small zone of beta hemolysis.



Colonies on SBA




The same blood agar plate examined with transmitted light allows you to see the small zone of beta hemolysis.

Based on the gram stain and colony morphology my preliminary ID was possible Listeria.  I then performed several direct tests to confirm the ID.  The catalase, bile esculin, and CAMP tests were all positive.  Growth in motility test medium showed growth away from the stab line in an “umbrella” shaped.  The crystal GP confirmed the isolate was Listeria monocytogenes. 

If we refer back to the case study, the elderly man had a fever which is indicative of infection and stiffness in the neck is the most recognizable symptom of a CNS infection.  His symptoms correlate with Listeria monocytogenes which is one of the bacterial agents that commonly causes meningoencephalitis.