COMPARISON OF BACTEC-9240 AND DIFCO ESP BLOOD CULTURE SYSTEMS FOR DETECTION OF ORGANISMS FROM VIALS WHOSE ENTRY WAS DELAYED

A comparison of the Bactec 9240 (Becton-Dickinson, Sparks, Md.) and Di fco ESP (Difco Laboratories, Detroit, Mich.) instruments for the detec tion of organism growth from vials whose entry was delayed was evaluat ed. The instruments' capabilities for organism recovery, time to detec tion, rates of false-positive results, and numbers of vials in which g rowth was not detected were made by using seeded blood culture vial pa irs and controls with and without delayed entry. Bactec 9240 and Difco ESP aerobic and anaerobic vials were inoculated with human blood and were seeded with organism growth from 18 species, including obligate a erobic, anaerobic, and facultative anaerobic organisms. Each organism was tested in triplicate at 0, 8, 24, 36, and 48 h and was incubated a t both room temperature (RT) and 35 degrees C. Two separate phases of the study were performed, each with a different version of Bactec 9240 software. Overall, detection of growth in vials with delayed entry in to either the Bactec 9240 or the Difco ESP instrument resulted in an i ncreased total time to detection with incubation at both RT and 35 deg rees C compared with the total time to detection for nondelayed vials. However, false-positive results and vials in which growth was not det ected were minimal, and delayed entry did not require routine entry or exit subcultures for either system. Analysis of individual time point s and incubation temperatures for the detection of all organisms sugge sted that Difco ESP vials delayed by up to 8 h may be incubated at 35 degrees C (100% detection) and vials delayed for longer than 8 h may r emain at RT. Bactec 9240 vials may be incubated at 35 degrees C for up to 24 h with a minimal loss of detection (97.9% detection), and vials delayed for more than 24 h should remain at RT for optimal recovery o f organism growth.