The recovery of bacteria and fungi from blood cultures was compared in conventional tryptic soy broth (TSB) bottles and in TSB bottles with an agarcoated slide attachment. A total of 2,662 sets of blood cultures, including 413 that were positive (15.5%), were evaluated. Significantly more gram-positive and gram-negative bacteria were recovered in the slide culture bottles than in conventional bottles (299 versus 253 isolates). Growth of gram-positive organisms and fungi was detected in the

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... culture bottles 24 to 48 h earlier than in the TSB bottles. In addition, 76% of the isolates in the slide culture system were detected on the agar slide. In comparison, only 40% of the isolates in the TSB bottles were detected initially by blind subculturing. The incidences of contamination were 2.7% (71 cultures) for the slide culture system and 1.5% (39 cultures) for the TSB bottles. There have been numerous studies documenting the efficacy of biphasic blood cultures for the recovery of fungi from patients with suspected fungemia (3, 6, 9) . Although this technique was described originally for the isolation of Brucella spp. (4), very few investigators have used it for the recovery of bacteria from blood cultures (5, 10). A modification of the standard biphasic blood culture system has been developed by Roche Diagnostics (Div. Hoffmann-La Roche, Inc.). The system consists of a routine blood culture bottle onto which can be attached a cylinder that contains an agar-coated slide with chocolate agar on one side and MacConkey and malt agars on the other side. The blood culture broth medium can then be subcultured onto the agar slide by tipping the bottle at the time of macroscopic examination. Bryan reported both better and faster recovery of organisms with this system than with a conventional system (2). However, these results were inconclusive because different media and blood volumes were used in the two systems. Thus, to extend these observations we conducted a comparative study with similar broths and equal blood volumes and examined the efficacy of the slide culture system in the microbiology laboratory of a large U.S. teaching hospital. MATERIALS AND METHODS During this study, three blood culture broths were inoculated: the Roche bottle that contained 70 ml of tryptic soy broth (Roche Diagnostics) with 0.05% sodium polyanetholesulfonate (slide culture bottle); a 100-ml bottle that contained tryptic soy broth with 0.025% sodium polyanetholesulfonate (TSB bottle; Difco); and a 100-ml bottle that contained Thiol broth with 0.025% sodium polyanetholesulfonate (Thiol bottle; Difco). Approximately 20 ml of blood was collected aseptically by venipuncture from patients with suspected bacteremia or fungemia, and an equal volume (5 to 7 ml) was placed into each bottle. Upon receipt at the laboratory, the TSB bottle was vented chronically with a sterile cotton-plugged needle, and the Thiol bottle was not vented to promote recovery of anaerobes (12). Both the TSB and Thiol bottles were examined visually twice during the first 24 h and daily thereafter for evidence of microbial growth. Gram stains were performed on any bottles with macroscopic evidence of growth. In addition, blind subcultures to chocolate agar plates were made from the TSB and Thiol bottles on days 1 and 3 of incubation. Before incubating the Roche slide culture bottles, the agar-coated slide system was attached to the bottle by removing the bottle cap, flaming the neck of the bottle, and screwing the slide unit securely in place. These initial manipulations were performed in a laminar flow safety cabinet to minimize contamination. All subsequent manipulations were performed at the bench. No attempt was made to keep the slide culture system anaerobic. The cultures were examined twice during the first 24 h and daily thereafter, as for the TSB and Thiol bottles. Subcultures of the slide culture bottles were performed immediately after placement of the slide unit and, subsequently, at the time of macroscopic examination by transiently inverting the bottle to allow the blood-containing medium to flow over the agar slide. Thus, the first subculture of the slide culture bottles was performed on the average 6 to 525 on May 4, 2020 by guest