Cerebrospinal fluid (CSF)

Bacterial meningitis is a life – threatening condition requiring rapid evaluation and therapy. Streptococcus pneumoniae and Neisseria meningitidis are the primary pathogens. In neonates, Group B beta – hemolytic streptococcus and Escherichia coli are also important pathogens. Listeria monocytogenes is a rare potential cause in all age groups.

Setup Often several tubes are submitted for analysis. Preferentially, we will process tube number 3 in microbiology if 4 tubes are collected and will process tube number 2 if 3 tubes are collected.

Direct Examination

Examine the fluid for colour, xanthochromia, turbidity and the presence of visible blood or clots. Record the observations and volume.

If Cryptococcus, India ink preparation or Fungal culture is requested perform a cryptococcal antigen test on the supernatant or from the original specimen.

Centrifuge the remaining specimen at 3000 rpm x 10 minutes.

Transfer the supernatant to a sterile tube which can be used for biochemical, viral, molecular, Cryptococcal antigen or serological tests if required. Label clearly remaining supernatant and refrigerate.

Use the sediment to prepare Gram stain and to inoculate the culture media listed below. Label clearly any remaining sediment and refrigerate.

See Gram stain preparation See Gram stain procedure

Media Incubation
Blood Agar (BA) CO2, 35°C x 48 hours
Chocolate Agar (CHOC) CO2, 35°C x 48 hours
Wilkins Chalgren Agar (WC) AnO2, 35°C x 48 hours
Thioglycolate broth (THIO) O2, 35°C x 48 hours (If shunt 7days)

If fungus or Crytococcus requested add:

Sabouraud’s Heart Infusion Agar (SABHI) O2, 30°C x 4 weeks

If more than one test is ordered, call the ordering physician and request prioritization.

For routine C&S, prepare a Gram smear using a drop of CSF and then directly inoculate the culture media listed above.

Followup Identify fully and perform susceptibilities on all isolates.

Reporting

Gram stain

Report the presence or absence of organisms and WBCs. Do not quantitate.

Culture

Negative “No growth”.

Positive Report all isolates with appropriate sensitivities. Do not quantitate except if it is from the fluid medium only – add Comment “From broth culture only, indicative of small numbers and/or contamination.”

Report all positive stain, latex or culture results ASAP by telephone to the ward/ordering physician.

References P.R. Murray, E.J. Baron, M.A. Pfaller, R.H. Yolken. 2003. Manual of Clinical Microbiology, 8th ed. ASM Press, Washington, D.C.

H.D. Izenberg. 2003. Blood Cultures-General Detection and Interpretation, p.3.4.1.1-3.4.1.19 In Clinical Microbiology Procedures Handbook, 2nd ed. Vol.1 ASM Press, Washington, D.C.

QMP-LS Practice Guidelines – Cerebral Spinal Fluid