The rapid detection of microorganisms from blood culture is important because of its impact on appropriate selection and duration of antimicrobial therapy. The present study compared the ability of a rapid DNA probe assay to detect bacterial growth in blood culture specimens to their detection by continuous-monitoring blood culture systems (CMBCS). A total of 1700 blood cultures collected from 3 intensive care nurseries were analyzed. A 3cc aliquot of blood was removed from each culture during early incubation (mean 14 hrs), processed and analyzed by the DNA probe.

Results:

  1. a

    131 (7.7%) of 1700 blood cultures were positive by CMBCS yielding 137 organisms.

  2. b

    Coagulase negative staphylococcus (CNS) accounted for 92 (67%) of the isolated organisms. Other organisms isolated included: Klebsiella, E. coli, Enterococcus, Enterobacter, Serratia, S.aureus, P. Aeruginosa, S. agalactiae, S. mitis, S. salivarius, and S. bovis.

  3. c

    Of 27 + cultures detected by CMBCS between 0 and 12 hrs, 23 (85%) were detected by probe. Of 72 + cultures detected by CMBCS between 12 and 24 hrs, 30 (42%) were detected by probe.

    Of 30 + cultures detected by CMBCS between 24 and 48 hrs, 4 (13%) were detected by probe.

    Of 2 organisms detected by CMBCS beyond 48 hrs, both were CNS. One was detected at 51 hrs and the other at 5 days, the latter being clinically insignificant. Neither was detected by probe.

  4. d

    78% of + cultures were detected by CMBCS in ≤ 24 hrs. Of these, 54% were detected by probe. 99% of clinically significant organisms were detected by CMBCS in ≤ 48 hrs. Of these, 44% were detected by probe.

Conclusions: (1) These data demonstrate that this DNA probe is less sensitive than currently employed CMBCS in the early detection of bacterial growth in neonatal blood cultures. (2) Automated CMBCS are sufficiently sensitive to aid in clinical decisions regarding the continuance of antibiotic therapy following 48 hours of culture incubation.