Serial PCR genetic load determination in the surgical management of pneumococcal intracranial sepsis

Aspirated intracranial fluid, in the surgical management of intracranial sepsis, may not culture an organism due to the previous administration of antibiotics. We have sought to utilise polymerase chain reaction (PCR) to determine the cause of culture-negative sepsis and in monitoring response to therapy.

This was a retrospective review of five cases of Streptococcus pneumoniae intracranial sepsis. Samples were analysed using real-time quantitative PCR targeting the pneumococcal lytA gene and the number of genome copies per microlitre of sample determined.

Streptococcus pneumoniae sepsis was diagnosed by PCR in five culture-negative cases comprising: ventriculitis (×3), subdural empyema and meningitis. Serial serum inflammatory markers (CRP and WBC) and number of genome copies were graphically plotted over the duration of inpatient stay for cases requiring surgical drainage of recurrent collections or external ventricular drainage. A correlation was demonstrated between change in bacterial genomic load and serum inflammatory markers, reflecting similar changes in clinical state.

This is the first report of the use of serial quantitative PCR in monitoring the course of intracranial sepsis secondary to S. pneumoniae. Further work is required to determine the precise relationship between serum inflammatory markers, clinical state and bacterial load: do changes in one precede the other? Furthermore, a threshold value for number of genome copies in cerebrospinal fluid/aspirate samples has yet to be defined.