Detection of bacterial DNA in cerebrospinal fluid (CSF) samples.
The polymerase chain reaction (PCR) is a molecular tool used for the detection of microorganisms. For bacterial detection the reaction is used to amplify DNA sequences which are specific to the target pathogen.
PCR tests are available as an adjunct diagnostic procedure for some organisms, in particular:
- Neisseria meningitidis
- Streptococcus pneumoniae
- Listeria monocytogenes
At present PCR tests do not replace conventional bacterial culture.
In some cases, especially when antibiotics have been given to the patient before the collection of CSF, PCR tests can be used to improve the sensitivity of detection. PCR will detect both live and dead bacteria.
CSF should be collected sequentially into 3 or more separate containers together with a fluoride sample for glucose estimation.
Each container must be numbered indicating the order of collection. The first and the third specimens are used for microbiological examination and the second specimen for biochemical analysis.
Aseptic technique should be employed for sample collection.
Sterile white top universal
A minimum of 200μL is required for each PCR test
Limitations and restrictions
The use of bacterial PCR for CSF specimens should be discussed with a Consultant Microbiologist by the requesting team.
The sensitivity and specificity of DNA detection tests depends on the quality/type of the sample and the test performed.
Low volume samples: CSF received below the minimum volume may be processed, but will be diluted as required for testing. Diluting samples can impact test sensitivity, meaning that lower concentrations of bacterial DNA may no longer be detectable causing false negative results. The result report will bear a comment alerting the user to this. It is recommended that users send the required volume for extraction and testing.
Next day following receipt at the reference laboratory
Micropathology Ltd, Venture Centre, University of Warwick Science Park, Sir William Lyons Road, Coventry, CV4 7EZ
Bacterial PCR tests should be requested at the time of sampling and sent with the CSF sample as far as possible.
Where possible a separate sample should be provided to be sent to the referral laboratory for testing. This will allow for the sample to remain unopened prior to PCR investigation eliminating the risk of sample contamination.
If bacterial PCR tests are requested after the sample has been processed by Microbiology at James Cook, the request should be made via telephone to the Consultant Microbiologist.