Studies On Enriching Pathogenic Bacteria From Cerebrospinal Fluid For Improving Rate Of Positive Cultivation By Centrifugalization

Objective To explore the method by centrifugalization to enrich bacteria from cerebrospinal fluid(CSF) of patients, improving rate of positive cultivation by condensing pathogenic bacteria.Methods Pathogenic bacteria from CSF were enriched by centrifugalization with high speed. Leukocytes were counted in microscope and the quantity of the protein was detected by automatic biochemical analyzer. Streptococcus Pneumoniae , Neisseria Meningitidis and Haemophilus Influenzae were respectively added to CSF with different leukocytes and protein concentration, and they were centrifuged at different centrifugal force to compare the effect of them on centrifugal force. The supernatant and the sediment were respectively inoculated onto agar plates, 10μl of which each was drawn and was observed under microscope simultaneously. After 24 to 48h of incubation, the number of bacteria in the cerebrospinal fluid supernatant fluid and sediment were determined quantitatively by colony counts. Comparison to variation of biochemical events and susceptibility tests of the bacteria was done after centrifugalization.Results As the relative centrifugal force(RCF) was 5753xg and centrifugalization time was 15min, the effect of enrichments on Streptococcus Pneumoniae, Neisseria Meningitidis and Haemophilus Influenzae was optimal. With the quantity of the protein in CSF increasing, the RCF to enrich pathogenic bacteria would be elevated and pathogenic bacteria were condensed mostly as the RCF was 5753×g , instead, the enrichment ratio decreased as the RCF was over 5753xg. When leukocytes concentration was different, there was no significant difference among groups(P>0.05). When RCF was equal to or less than 5753xg, morphous, biochemical events and susceptibility tests of bacteria kept unchanged comparing with before centrifugalization. However, on the condition of RCF over 5753xg, the result of cultivation was negative and we could not observe intact bacteria under microscope.Conclusions Bacteria which concentration less than 10~2 /ml in CSF can not be enriched by centrifugalization. Bacteria which concentration more than or equal to 10~2/ml in CSF can be enriched effectively by means of centrifugalization when the relative centrifugal force is 5753xg and centrifugalization time is 15min and the rate of positive cultivation of pathogenic bacteria in clinical specimen can be improved by centrifugalization with high speed.