Clinical comparison of the recoveries of bloodstream pathogens in Septi-Chek brain heart infusion broth with saponin, Septi-Chek tryptic soy broth, and the isolator lysis-centrifugation system

Abstract

The recoveries of microorganisms in the Septi-Chek biphasic tryptic soy broth (TSB) and Isolator blood culturing systems were compared with the recovery in Septi-Chek biphasic brain heart infusion broth supplemented with the lytic agent saponin (L-BHIB; Roche Diagnostics, Division of Hoffmann-La Roche Inc.). A total of 5,096 TSB-L-BHIB blood culture sets and 1,778 Isolator-L-BHIB sets were evaluated. There were 435 pathogenic organisms recovered in 413 (8.1%) of the TSB-L-BHIB cultures, with 348 organisms in the TSB bottles and 370 in the L-BHIB bottles (P less than 0.05). Significantly more yeast isolates were recovered in the L-BHIB system (P less than 0.01). Terminal subculture of the L-BHIB system was required to detect 13 clinically significant organisms. Significantly more organisms were recovered in the L-BHIB bottles than with the Isolator system (P less than 0.001), including Torulopsis glabrata, coagulase-negative staphylococci, and Pseudomonas species. The time required for detection of all major groups of organisms was the same in both comparisons. However, detection of microbial growth in the L-BHIB bottles required macroscopic inspection of the attached agar slide unit and the use of terminal subcultures after 7 days of incubation. The primary advantage of the biphasic L-BHIB system when compared with either the biphasic TSB system or the Isolator system was improved recovery of fungi.