Microbiology Laboratory


Written by MicroDok

AIM: To isolate bacteria from cerebrospinal fluid (CSF) specimen as an aid in the diagnosis of cerebrospinal meningitis.

MATERIAL/APPARATUS: Cerebrospinal fluid (CSF) specimen, blood agar (BA), chocolate agar (CA), Bunsen burner, inoculating loop, incubator, anaerobic jar, MacConkey agar (MCA).

NOTE: The CSF specimen should be collected only by an experienced medical officer or health worker.  A lumber puncture is required to obtain the CSF specimen and should be done aseptically to avoid contamination. This is very important so as not to avoid introducing any contaminant into the CSF – which is a sterile fluid of the body. CSF is free from normal microbial flora and thus its collection and handling in the laboratory should be done aseptically. The examination/culture of CSF specimen should not be delayed like other specimens, and the results of tests should be immediately reported to the physician as soon as they become available. If the CSF specimen is from a newborn patient, MacConkey agar (MAC) should be used in addition with the blood agar (BA) and chocolate agar (CA). MAC and BA plates should be incubated aerobically while the CA plate should be incubated anaerobically. The CSF specimen comes to the microbiology laboratory in the string used for its collection, thus primary inoculants required for inoculation/culture should be obtained by releasing a drop on each of the culture media plates.


  1. Label the CA and BA plates with the patient’s name and laboratory number.
  2. Inoculate the CSF specimen on each of the CA and BA plates.
  3. Incubate the BA plate in the incubator at 37oC overnight.
  4. Incubate the CA plate in the anaerobic jar at 37oC overnight.
  5. After incubation, examine both plates for significant bacteria growth.
  6. Perform biochemical testing on significant bacterial isolates.
  7. Perform antimicrobial susceptibility testing only when a significant bacterium is isolated.


Look especially for colonies that could be Escherichia coli or other coliform in the MAC plate and report. Look particularly for Neisseria meningitides, Streptococcus pneumonia, and Haemophilus influenzae on both the CA and BA plates and report appropriately.

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