CSF culture is used for specific diagnosis of bacterial meningitis. Patients commonly present with severe headache, fever, neck stiffness, and meningeal signs, mental status changes, and signs of systemic toxicity.
Method
CSF is inoculated onto sheep blood and chocolate agar, incubated aerobically. Broth media may be inoculated. Special media or culture conditions may be used for non " “community-acquired meningitis, such as infections associated with trauma and prosthetic implants.
Turnaround time: Cultures are incubated for 96 hours. Additional time is required for isolate identification, susceptibility testing, and further characterization, as needed.
Special Collection and Transport Instructions
CSF is collected by needle aspiration after preparation of the puncture site in a manner consistent with a surgical site preparation.
Fluid is transported in a sterile container or tube with a tight-fitting lid.
CSF should be transported at room temperature; do not refrigerate or freeze for transport.
Specimens submitted for bacterial culture are also acceptable for fungal or mycobacterial stains and culture, antigen testing, and VDRL, if sufficient volume of fluid is submitted.
Interpretation
Expected results: No growth. False-negative cultures may be caused by low pathogen concentration in CSF, especially when low-volume samples are submitted, or prior antibiotic therapy.
Positive results: Positive CSF culture supports a specific diagnosis of meningitis. False-positive cultures may be caused by contamination with endogenous skin flora. For most bacterial pathogens, CSF samples in patients with acute bacterial meningitis usually show increased WBCs (PMNs predominate), increased protein, and decreased glucose.
Limitations
A broad etiology, which may require a number of different tests for diagnosis, may be considered for patients presenting with signs and symptoms of meningitis. The volume of CSF submitted is often insufficient for optimal sensitivity for the range of tests requested.