Clinical evaluation of lysis-centrifugation technique and a biphasic bottle system for blood culture

The lysis centrifugation technique (Isolator, DuPont) for blood culture was compared with a system with biphasic medium in bottles. The Isolator was filled with 10 ml of blood once. One aerobic and one anaerobic bottle were injected 3 times with 2.5 ml of blood each. Organisms were detected in 90/748 blood cultures; 26 of which were contaminants. 34 pathogens were detected by both methods, 12 with the Isolator only and 18 with the 3 bottle pairs only. The first pair of bottles revealed 45/52 isolates, the second and third pairs gave an additional 6 and 1 isolate respectively. The contamination rate was 2.3% for the Isolator, which is lower than earlier reported, and 1.3% for the bottles. The most common pathogens were Escherichia coli, Pseudomonas aeruginosa and Streptococcus pneumoniae. The Isolator gave a faster diagnosis in 23 of the 34 cases. No decrease in the recovery rate was seen after 8 h, the longest recommended transport time for the Isolator tubes. One Isolator gave the same yield as the first pair of bottles and combining the methods increased the yield 25% compared to either method alone.