Clinical laboratory comparison of lysis-centrifugation and BACTEC radiometric blood culture techniques

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Abstract
The lysis-centrifugation technique (ISOLATOR) and the radiometric blood culture technique (BACTEC) were compared on 1000 blood cultures. Blood (16 ml) was distributed: 8 ml into an ISOLATOR 7.5 microbial tube and 4 ml each into BACTEC 7C and 8B bottles. The concentrate from the ISOLATOR tubes was inoculated under a laminar-flow hood onto 7 sheep blood agar plates (1 incubated in CO2 and 1 incubated anaerobically), 1 chocolate agar plate and 1 brain heart infusion agar plate. Of 91 blood specimens obtained that yielded clinically significant organisms [bacteria, fungi], 52 were positive by both systems, 27 were positive by the ISOLATOR system only and 12 were positive by the BACTEC system only. From the positive blood specimens, 97 clinically significant organisms were isolated: 57 by both systems, 27 by the ISOLATOR system only and 13 by the BACTEC system only. Of the 57 organisms detected by both systems, 28 were detected simultaneously, 13 were detected earlier by the ISOLATOR system and 16 were detected earlier by the BACTEC system. Isolated colonies were obtained earlier by the ISOLATOR system in 40 cases and by the BACTEC system in 5 cases. Organisms determined to be contaminants by thorough chart review were isolated from 138 ISOLATOR tubes. In 98 instances, these were represented by 1 colony of Staphylococcus epidermidis, .alpha.-hemolytic streptococci or diphtheroids. The ability to determine colony-forming units per milliliter with the ISOLATOR system did not help differentiate clinically significant organisms from contaminants.

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