Clinical comparison of aerobic, hypertonic, and anaerobic culture media for the radiometric detection of bacteremia

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Abstract
The BACTEC 225 was used to test 5811 routine blood cultures over a 20 mo. period. Aerobic, anaerobic and hypertonic media were employed. The BACTEC 225 detected 511 cultures; 407 of these were considered significant organisms; 104 were presumed contaminants. Of the significant positive cultures, 15% were detected within the first 12 of incubation, 52% within 24 h, 82% within 48 h and 92% within 72 h. Aerobic, anaerobic and hypertonic media are recommended for each venipuncture since 56 cultures were isolated from the aerobic medium only, 110 from the anerobic medium only and 94 from the hypertonic medium only. There were 16 patients who had multiple venipunctures from which organisms were repeatedly isolated from only 1 medium; 2 from the aerobic medium, 4 from the anaerobic medium and 10 from the hypertonic medium only. Detection times were not significantly different for the aerobic and hypertonic media; there were 5 patients with multiple venipunctures in which growth was detected radiometrically at least 48 h earlier in the hypertonic than in the aerobic medium. False-positive growth index readings were noted in 1085 (19%) of the aerobic vials, 11 (0.19%) of the anaerobic vials and 104 (1.7%) of the hypertonic vials. With some false-positive aerobic and hypertonic vials, microorganisms were isolated from at least 1 of the companion vials. Using 5% CO2 to flush the aerobic vials decreased the number of false positives to about 6% of the total.